MedWorm.com provides a medical RSS filtering service. Over 6000 RSS medical sources are combined and output via different filters. This feed contains the latest items from the 'Magnetic Resonance in Medicine' source. Thu, 09 Feb 2012 03:37:46 +0100 http://www.medworm.com/index.php?rid=5661527&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24189 AbstractMR scans are sensitive to motion effects due to the scan duration. To properly suppress artifacts from nonrigid body motion, complex models with elements such as translation, rotation, shear, and scaling have been incorporated into the reconstruction pipeline. However, these techniques are computationally intensive and difficult to implement for online reconstruction. On a sufficiently small spatial scale, the different types of motion can be well approximated as simple linear translations. This formulation allows for a practical autofocusing algorithm that locally minimizes a given motion metric — more specifically, the proposed localized gradient‐entropy metric. To reduce the vast search space for an optimal solution, possible motion paths are limited to the motion measured f... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5661527 Wed, 01 Feb 2012 05:00:00 +0100 5661527 http://www.medworm.com/index.php?rid=5651966&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24198 This study used a 4 T magnet to examine the influence of foot orientation on the appearance and quantification of muscle magnetic resonance spectra from the soleus and the vastus lateralis. For each individual, intramyocellular lipid, extramyocellular lipid, and creatine concentrations were quantified in the soleus and the vastus lateralis during one session. Foot orientation was found to influence the appearance of muscle spectra from the soleus but not from the vastus lateralis. It was concluded that quantifying intramyocellular lipid by the standard LCModel using a water reference may be more appropriate than using a creatine reference in the presence of residual dipolar couplings. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc. (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651966 Wed, 01 Feb 2012 05:00:00 +0100 5651966 http://www.medworm.com/index.php?rid=5651965&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24187 This study investigates whether so‐called super‐resolution reconstruction methods can increase the resolution in the slice selection direction and, as such, are a viable alternative to direct high‐resolution acquisition in terms of the signal‐to‐noise ratio and acquisition time trade‐offs. The performance of six super‐resolution reconstruction methods and direct high‐resolution acquisitions was compared with respect to these trade‐offs. The methods are based on iterative back‐projection, algebraic reconstruction, and regularized least squares. The algorithms were applied to low‐resolution data sets within which the images were rotated relative to each other. Quantitative experiments involved a computational phantom and a physical phantom containing structures of known... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651965 Wed, 01 Feb 2012 05:00:00 +0100 5651965 http://www.medworm.com/index.php?rid=5651964&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24193 AbstractDiffusion‐weighted spectroscopy is a unique tool for exploring the intracellular microenvironment in vivo. In living systems, diffusion may be anisotropic, when biological membranes exhibit particular orientation patterns. In this work, a volume selective diffusion‐weighted sequence is proposed, allowing single‐shot measurement of the trace of the diffusion tensor, which does not depend on tissue anisotropy. With this sequence, the minimal echo time is only three times the diffusion time. In addition, cross‐terms between diffusion gradients and other gradients are cancelled out. An adiabatic version, similar to localization by adiabatic selective refocusing sequence, is then derived, providing partial immunity against cross‐terms. Proof of concept is performed ex vivo on ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651964 Wed, 01 Feb 2012 05:00:00 +0100 5651964 http://www.medworm.com/index.php?rid=5651980&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24190 In this study, the signal‐to‐noise ratio of hyperpolarized 129Xe human lung magnetic resonance imaging was compared at 1.5 T and 3 T. Experiments were performed at both B0 fields with quadrature double Helmholtz transmit–receive chest coils of the same geometry with the same subject loads. Differences in sensitivity between the two field strengths were assessed from the signal‐to‐noise ratio of multi‐slice 2D 129Xe ventilation lung images obtained at the two field strengths with a spatial resolution of 15 mm × 4 mm × 4 mm. There was a systematically higher signal‐to‐noise ratio observed at 3 T than at 1.5 T by a factor of 1.25. Mean image signal‐to‐noise ratio was in the range 27–44 at 1.5 T and 36–51 at 3 T. T of 129Xe gas in the partially inflated lungs was meas... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651980 Tue, 31 Jan 2012 05:00:00 +0100 5651980 http://www.medworm.com/index.php?rid=5651979&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24188 AbstractA finite difference method was used to simulate the electric fields induced in the model by a gradient wire pattern. The pattern simulated corresponded to a design used to perform peripheral nerves stimulation experiments. The size (187.8, 169.02, and 150.24 cm tall) and position (brain and neck mode) of the model, relative to the magnet, as well as the voxel dimensions (3, 6, and 9 mm) of the model were varied to assess the effect on the simulation. The locations of stimulation reported from an experiment were classified according to nerve branch and compared with the peak‐simulated electric fields. Model size and location affected the magnitude of the electric field, but not the position. Model resolution affected the location of the peak field. For the smallest resolution inve... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651979 Tue, 31 Jan 2012 05:00:00 +0100 5651979 http://www.medworm.com/index.php?rid=5651978&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24186 AbstractAdvances in modern magnetic resonance imaging (MRI) pulse sequences have enabled clinically practical cortical bone imaging. Human cortical bone is known to contain a distribution of T1 and T2 components attributed to bound and pore water, although clinical imaging approaches have yet to discriminate bound from pore water based on their relaxation properties. Herein, two clinically compatible MRI strategies are proposed for selectively imaging either bound or pore water by utilizing differences in their T1s and T2s. The strategies are validated in a population of ex vivo human cortical bones, and estimates obtained for bound and pore water are compared to bone mechanical properties. Results show that the two MRI strategies provide good estimates of bound and pore water that correla... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651978 Tue, 31 Jan 2012 05:00:00 +0100 5651978 http://www.medworm.com/index.php?rid=5651977&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24182 AbstractProton magnetic resonance spectroscopic imaging of the prostate can detect and localise tumour tissue in patients with prostate cancer. Pattern recognition methods have the potential to discriminate tumour from normal tissue using the spectral patterns of magnetic resonance spectroscopic imaging data thus providing a powerful tool for diagnosis and monitoring treatment of prostate cancer. Prostate magnetic resonance spectroscopic imaging data acquisition has been optimized for a flat baseline, including a long echo time and the use of water and fat suppression pulses. Despite this acquisition method, lipid resonances may still occur particularly at the margins of the prostate. Correcting the baseline by removing lipid artifacts is, therefore, a necessary processing step. We propose... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651977 Tue, 31 Jan 2012 05:00:00 +0100 5651977 http://www.medworm.com/index.php?rid=5651976&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24145 AbstractA new MRI technique to map the oxygenation of venous blood is presented. The method uses velocity‐selective excitation and arterial nulling pulses, combined with phase sensitive signal detection to isolate the venous blood signal. T2 of this signal along with a T2–Y calibration curve yields estimates of venous oxygenation in situ. Results from phantoms and healthy human subjects under normoxic and hypoxic conditions are shown, and venous saturation levels estimated from both sagittal sinus and gray matter–based regions of interest are compared with the related techniques TRUST and QUIXOTIC. In addition, combined with an additional scan without arterial nulling pulses, the oxygen saturation level on arterial side can also be estimated. Magn Reson Med, 2012. © 2012 Wiley Perio... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651976 Tue, 31 Jan 2012 05:00:00 +0100 5651976 http://www.medworm.com/index.php?rid=5651975&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24172 AbstractRecently, spatially two‐dimensional selective radiofrequency excitations based on the PROPELLER trajectory have been presented and were applied to minimize partial volume effects in single‐voxel MR spectroscopy. Thereby, residual side excitations appeared due to limitations of the Voronoi diagram that was used to consider the nonconstant sampling density, and trajectory distortions caused by eddy currents varying between the differently rotated blades. In this extension, one of the refocusing radiofrequency pulses of a PRESS‐based pulse sequence is applied in the blip direction of each segment to eliminate the side excitations. This corresponds to an infinitely dense sampling of the blade and the required sampling density correction can easily be calculated. Thus, signal cont... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651975 Tue, 31 Jan 2012 05:00:00 +0100 5651975 http://www.medworm.com/index.php?rid=5651974&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24162 We describe the gamma capillary transit time model, a generalized impulse response model for DCE‐MRI that mathematically unifies the Tofts‐Kety, extended Tofts‐Kety, adiabatic tissue homogeneity, and two‐compartment exchange models. By including a parameter (α−1) representing the width of the distribution of capillary transit times within a tissue voxel, the GCTT model discriminates tissues having relatively monodisperse transit time distributions from those having a large degree of heterogeneity. All five models were compared using in vivo data acquired in three brain tumors (one glioblastoma multiforme, one pleomorphic xanthoastrocytoma, and one anaplastic meningioma) and Monte Carlo simulations. Our principal findings are : (1) The four most commonly used models for dynamic c... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651974 Tue, 31 Jan 2012 05:00:00 +0100 5651974 http://www.medworm.com/index.php?rid=5651973&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24185 AbstractVibration synchronized magnetic resonance imaging of harmonically oscillating tissue interfaces is proposed for cardiac magnetic resonance elastography. The new approach exploits cardiac triggered cine imaging synchronized with extrinsic harmonic stimulation (f = 22.83 Hz) to display oscillatory tissue deformations in magnitude images. Oscillations are analyzed by intensity threshold‐based image processing to track wave amplitude variations over the cardiac cycle. In agreement to literature data, results in 10 volunteers showed that endocardial wave amplitudes during systole (0.13 ± 0.07 mm) were significantly lower than during diastole (0.34 ± 0.14 mm, P < 0.001). Wave amplitudes were found to decrease 117 ± 40 ms before myocardial contraction and to increase 75 ± 31 ms b... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651973 Tue, 31 Jan 2012 05:00:00 +0100 5651973 http://www.medworm.com/index.php?rid=5651972&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24151 AbstractFast methods using balanced steady‐state free precession have been developed to reduce the scan time of T1 and T2 mapping. However, flip angle (FA) profiles created by the short radiofrequency pulses used in steady‐state free precession deviate substantially from the ideal rectangular profile, causing T1 and T2 mapping errors. The purpose of this study was to develop a FA profile correction for T1 and T2 mapping with Look‐Locker 2D inversion recovery steady‐state free precession and to validate this method using 2D spin echo as a reference standard. Phantom studies showed consistent improvement in T1 and T2 accuracy using profile correction at multiple FAs. Over six human calves, profile correction provided muscle T1 estimates with mean error ranging from excellent (−0.6%... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651972 Tue, 31 Jan 2012 05:00:00 +0100 5651972 http://www.medworm.com/index.php?rid=5651971&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24184 AbstractDivalent manganese ion (Mn2+) is a widely used T1 contrast agent in manganese‐enhanced MRI studies to visualize functional neural tracts and anatomy in the brain in vivo. In animal studies, Mn2+ is administered at a dose that will maximize the contrast, while minimizing its toxic effects. In rodents, systemic administration of Mn2+ via intravenous injection has been shown to create unique MRI contrast in the brain at a maximum dose of 175 mg kg−1. However, intravenous administration of Mn2+ results in faster bioelimination of excess Mn2+ from the plasma due to a steep concentration gradient between plasma and bile. By contrast, following subcutaneous injection (LD50 value = 320 mg kg−1), Mn2+ is released slowly into the bloodstream, thus avoiding immediate hepatic elimination... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651971 Tue, 31 Jan 2012 05:00:00 +0100 5651971 http://www.medworm.com/index.php?rid=5651970&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24183 AbstractThe conversion of hyperpolarized 13C pyruvate to metabolic products in the Krebs cycle provides valuable information about the metabolic status and the viability of the myocardium. Therefore, imaging methods must be able to spectrally discriminate different 13C metabolites. However, the requirement for spectral selectivity conflicts with the demands for rapid image acquisition and high spatial resolution in cardiac imaging. In this work, the feasibility of a balanced steady state free precession sequence with low flip angles was investigated in the pig heart after injection of hyperpolarized 13C1‐pyruvate. Using cardiac gating, it was possible to acquire 13C‐bicarbonate images within a single heartbeat (acquisition time 150 ms) without destroying the substrate signal from the h... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651970 Tue, 31 Jan 2012 05:00:00 +0100 5651970 http://www.medworm.com/index.php?rid=5651969&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24178 AbstractAn optimized echo‐planar spectroscopic imaging sequence is proposed to facilitate spatial mapping of triglyceride and total creatine content in the human heart. The sequence integrates local‐look field of view reduction, cardiac and respiratory gating, and dedicated reconstruction steps to account for gradient channel delays, field inhomogeneity, and phase incoherence due to residual motion. The technique is demonstrated in 12 volunteers in comparison to single voxel point‐resolved spectroscopy in the septal wall at 1.5 T. Triglyceride‐to‐water and total creatine‐to‐water ratios derived from echo‐planar spectroscopic imaging (0.48 ± 0.18% and 0.06 ± 0.03%) and point‐resolved spectroscopy (0.52 ± 0.17% and 0.07 ± 0.02%) were found to agree well. In the septal r... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651969 Tue, 31 Jan 2012 05:00:00 +0100 5651969 http://www.medworm.com/index.php?rid=5651968&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24177 AbstractThe proton T1 was measured at 132 μT in ex vivo prostate tissue specimens from radical prostatectomies of 35 patients with prostate cancer. Each patient provided two specimens. The NMR and MRI measurements involved proton repolarization, a field of typically 150 mT and detection of the 5.6‐kHz signal with a superconducting quantum interference device. Values of T1 varied from 41 to 86 ms. Subsequently, the percentages of tissue types were determined histologically. The theoretical image contrast is quantified for each case by δ = [1 – T1(more cancer)/T1(less cancer)]. A linear fit of δ versus difference in percentage cancer yields T1 (100% cancer)/T1 (0% cancer) = 0.70 ± 0.05 with correlation coefficient R2 = 0.30. Two‐dimensional T1 maps for four specimens demonstrate va... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651968 Tue, 31 Jan 2012 05:00:00 +0100 5651968 http://www.medworm.com/index.php?rid=5651967&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24166 AbstractThe emerging importance of nanoparticle technology, including iron oxide nanoparticles for monitoring development, progression, and treatment of inflammatory diseases such as arthritis, drives development of imaging techniques. Studies require an imaging protocol that is sensitive and quantifiable for the detection of iron oxide over a wide range of concentrations. Conventional signal loss measurements of iron oxide nanoparticle containing tissues saturate at medium concentrations and show a nonlinear/nonproportional intensity to concentration profile due to the competing effects of T1 and T2 relaxation. A concentration calibration phantom and an in vivo study of intra‐articular injection in a rat knee of known concentrations of iron oxide were assessed using the difference‐ult... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5651967 Tue, 31 Jan 2012 05:00:00 +0100 5651967 http://www.medworm.com/index.php?rid=5640116&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24169 AbstractAlternate ascending/descending directional navigation (ALADDIN) is a new imaging technique that provides interslice perfusion‐weighted and magnetization transfer (MT) asymmetry images. In this article, we investigated the effects of gradient imperfections on ALADDIN MT asymmetry (MTA) signals. Subtraction artifacts increasing with readout offsets were detectable in ALADDIN MTA images from an agarose phantom but not from a water phantom. Slice‐select offsets had no significant effect on the artifacts in MTA. The artifacts were suppressed by averaging signals over the readout gradient polarities independent of scan parameters. All these results suggested that the subtraction artifacts were induced by readout eddy currents. With suppression of the artifacts, ALADDIN signals in hum... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640116 Mon, 30 Jan 2012 09:14:36 +0100 5640116 http://www.medworm.com/index.php?rid=5640126&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24168 In conclusion, a systematic comparison of metabolic changes in cross sections of the upper and lower leg was performed. The results imply that pre‐exercise IMCL levels determine the degree of IMCL depletion after exercise. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc. (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640126 Fri, 27 Jan 2012 05:00:00 +0100 5640126 http://www.medworm.com/index.php?rid=5640125&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24167 AbstractCarnitine (Car) buffers excess acetyl‐CoA through the formation of acetylCar (AcCar). AcCar's acetyl group (AG‐AcCar) gives rise to a peak at 2.13 ppm in 1H MR spectra of skeletal muscle, whereas the trimethylammonium (TMA) groups of both, AcCar and Car, are thought to contribute to the TMA peak at 3.23 ppm. Surprisingly, in previous studies both resonances, AG‐AcCar and TMA, increased after exercise. The aim of this study was to assess if the exercise‐related TMA increase correlated with AcCar production. Magnetic resonance spectroscopic imaging (pulse repetition time/echo time = 1200/35 ms) was performed before and after prolonged exercise in the lower leg and thigh of eight runners and eight cyclists, respectively. TMA and AG‐AcCar increased after exercise (P < 0.00... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640125 Fri, 27 Jan 2012 05:00:00 +0100 5640125 http://www.medworm.com/index.php?rid=5640124&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24163 AbstractWideband steady‐state free precession (WB‐SSFP) is a modification of balanced steady‐state free precession utilizing alternating repetition times to reduce susceptibility‐induced balanced steady‐state free precession limitations, allowing its use for high‐resolution myelographic‐contrast spinal imaging. Intertissue contrast and spatial resolution of complete‐spine‐coverage 3D WB‐SSFP were compared with those of 2D T2‐weighted fast spin echo, currently the standard for spine T2‐imaging. Six normal subjects were imaged at 1.5 and 3 T. The signal‐to‐noise ratio efficiency (SNR per unit‐time and unit‐volume) of several tissues was measured, along with four intertissue contrast‐to‐noise ratios; nerve‐ganglia:fat, intradural‐nerves:cerebrospinal fl... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640124 Fri, 27 Jan 2012 05:00:00 +0100 5640124 http://www.medworm.com/index.php?rid=5640123&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24161 AbstractParamagnetic chemical exchange saturation transfer agents combine the benefits of a large chemical shift difference and a fast exchange rate for sensitive MRI detection. However, the in vivo detection of these agents is hampered by the need for high B1 fields to allow sufficiently fast saturation before exchange occurs, thus causing interference of large magnetization transfer effects from semisolid macromolecules. A recently developed approach named frequency‐labeled exchange transfer utilizes excitation pulses instead of saturation pulses for detecting the exchanging protons. Using solutions and gel phantoms containing the europium (III) complex of DOTA tetraglycinate (EuDOTA‐(gly)−4), it is shown that frequency‐labeled exchange transfer allows the separation of chemical ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640123 Fri, 27 Jan 2012 05:00:00 +0100 5640123 http://www.medworm.com/index.php?rid=5640122&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24164 AbstractAlthough phosphorus‐31 (31P) magnetic resonance spectroscopy holds potential as noninvasive tool to monitor treatment response of liver malignancies, the lack of appropriate coils has so far restricted its use to liver lesions close to the surface. A novel eight‐channel phased‐array dual‐tuned 31P/1H coil that can assess 31P metabolism in deeper liver tissue as well is presented in this article. Analysis of its performance demonstrates that this coil can provide good sensitivity across a width of 20 cm, thereby enabling magnetic resonance spectroscopic imaging (MRSI) scans that can fully cover axial views of the abdomen in lean subjects. In vivo results and reproducibility of 31P MRSI at 3 T of axial slices covering the full depth of the liver are shown in healthy volunteer... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640122 Fri, 27 Jan 2012 05:00:00 +0100 5640122 http://www.medworm.com/index.php?rid=5640121&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24179 AbstractDiffusion tensor microimaging at 16.4 T with 40 μm isotropic voxels was used to investigate anisotropic water diffusion in prostate tissue at spatial resolution approaching the cellular scale. Nine normal glandular tissue samples were collected from the peripheral zone of six formalin fixed radical prostatectomy specimens. Fibromuscular stromal tissue exhibited microscopic diffusion anisotropy (mean fractional anisotropy range 0.47–0.66) significantly higher (P < 0.01, Student's t‐test) than in epithelium‐containing voxels (mean fractional anisotropy range 0.31–0.54) in six of the seven normal tissue samples in which both compartments could be measured. Fiber tracking demonstrated principle stromal fiber directions consistent with myocyte orientation seen on light micro... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640121 Fri, 27 Jan 2012 05:00:00 +0100 5640121 http://www.medworm.com/index.php?rid=5640120&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24176 This article presents a series of electromagnetic simulations to determine the effects of pad size and geometry, relative permittivity value, as well as thickness on the transmit radiofrequency fields for neuroimaging at 7 T. For a 5‐mm thick pad, there is virtually no effect on the transmit field for relative permittivity values lower than ∼90. Significant improvements are found for values between 90 and ∼180. If the relative permittivity is increased above ∼180 then areas of very low transmit efficiency are produced. For a 1‐cm thick pad, the corresponding numbers are ∼60 and ∼120, respectively. Based upon the findings, a new material (barium titanate, relative permittivity ∼150) is used to produce thin (∼5 mm) dielectric pads which can easily be placed within a standar... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640120 Fri, 27 Jan 2012 05:00:00 +0100 5640120 http://www.medworm.com/index.php?rid=5640119&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24174 AbstractA computational pipeline combining texture analysis and pattern classification algorithms was developed for investigating associations between high‐resolution MRI features and histological data. This methodology was tested in the study of dentate gyrus images of sclerotic hippocampi resected from refractory epilepsy patients. Images were acquired using a simple surface coil in a 3.0T MRI scanner. All specimens were subsequently submitted to histological semiquantitative evaluation. The computational pipeline was applied for classifying pixels according to: a) dentate gyrus histological parameters and b) patients' febrile or afebrile initial precipitating insult history. The pipeline results for febrile and afebrile patients achieved 70% classification accuracy, with 78% sensitivi... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640119 Fri, 27 Jan 2012 05:00:00 +0100 5640119 http://www.medworm.com/index.php?rid=5640118&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24173 AbstractPhysiological noise artifacts, especially those originating from cardiac pulsation and subject motion, are common in clinical Diffusion tensor‐MRI acquisitions. Previous works show that signal perturbations produced by artifacts can be severe and neglecting to account for their contribution can result in erroneous diffusion tensor values. The Robust Estimation of Tensors by Outlier Rejection (RESTORE) method has been shown to be an effective strategy for improving tensor estimation on a voxel‐by‐voxel basis in the presence of artifactual data points in diffusion‐weighted images. In this article, we address potential instabilities that may arise when using RESTORE and propose practical constraints to improve its usability. Moreover, we introduce a method, called informed RES... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640118 Fri, 27 Jan 2012 05:00:00 +0100 5640118 http://www.medworm.com/index.php?rid=5640117&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24171 AbstractDetermining the MR compatibility of medical implants and devices is becoming increasingly relevant. In most cases, the heating of conductive implants due to radiefrequency (RF) excitation pulses is measured by fluoroptic temperature sensors in relevant tests for approval. Another common method to determine these heating effects is MR thermometry using the proton resonance frequency. This method gives good results in homogeneous phantoms. However in many cases, technical shortcomings such as susceptibility artifacts prohibit exact proton resonance frequency thermometry near medical implants. Therefore, this work aimed at developing a fast T1‐based method which allows controlled MR‐related heating of a medical implant while simultaneously quantifying the spatial and temporal temp... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5640117 Fri, 27 Jan 2012 05:00:00 +0100 5640117 http://www.medworm.com/index.php?rid=5621921&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24199 (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5621921 Tue, 24 Jan 2012 08:09:05 +0100 5621921 http://www.medworm.com/index.php?rid=5621920&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24200 AbstractSimulation and experimental results for parallel transmit. a: Transmit‐sensitivity patterns of a four‐channel system, b: offresonance map, c: Bloch‐simulated profiles, and d: experimental profiles. About 300 Hz off‐resonance offset was created by changing gradient‐shim values. Bmax = 0.5 (i.e., 50% of the full scale RF) was targeted through reVERSE method (with α = 0.8). Although the reVERSE pulse was 25% shorter than the original pulse, it maintained the profile fidelity with the reduced peak |B1,n| from the article by Lee et al (pp 353–362). (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5621920 Tue, 24 Jan 2012 08:09:04 +0100 5621920 http://www.medworm.com/index.php?rid=5612542&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24170 AbstractMultiexponential T2 relaxometry is a powerful research tool for detecting brain structural changes due to demyelinating diseases such as multiple sclerosis. However, because of unusually high signal‐to‐noise ratio requirement compared with other MR modalities and ill‐posedness of the underlying inverse problem, the T2 distributions obtained with conventional approaches are frequently prone to noise effects. In this article, a novel multivoxel Bayesian algorithm using spatial prior information is proposed. This prior takes into account the expectation that volume fractions and T2 relaxation times of tissue compartments change smoothly within coherent brain regions. Three‐dimensional multiecho spin echo MRI data were collected from five healthy volunteers at 1.5 T and myelin ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612542 Fri, 20 Jan 2012 05:00:00 +0100 5612542 http://www.medworm.com/index.php?rid=5612544&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22252792%26dopt%3DAbstract Authors: Romano A, Scheel M, Hirsch S, Braun J, Sack I Abstract White matter is composed primarily of myelinated axons which form fibrous, organized structures and can act as waveguides for the anisotropic propagation of sound. The evaluation of their elastic properties requires both knowledge of the orientation of these waveguides in space, as well as knowledge of the waves propagating along and through them. Here, we present waveguide elastography for the evaluation of the elastic properties of white matter tracts in the human brain, in vivo, using a fusion of diffusion tensor imaging, magnetic resonance elastography, spatial-spectral filtering, a Helmholtz decomposition, and anisotropic inversions, and apply this method to evaluate the material parameters of the corticospinal tr... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612544 Tue, 17 Jan 2012 05:00:00 +0100 5612544 http://www.medworm.com/index.php?rid=5612543&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22252850%26dopt%3DAbstract DREAM-a novel approach for robust, ultrafast, multislice B(1) mapping. Magn Reson Med. 2012 Jan 17; Authors: Nehrke K, Börnert P Abstract A novel multislice B(1) -mapping method dubbed dual refocusing echo acquisition mode is proposed, able to cover the whole transmit coil volume in only one second, which is more than an order of magnitude faster than established approaches. The dual refocusing echo acquisition mode technique employs a stimulated echo acquisition mode (STEAM) preparation sequence followed by a tailored single-shot gradient echo sequence, measuring simultaneously the stimulated echo and the free induction decay as gradient-recalled echoes, and determining the actual flip angle of the STEAM preparation radiofrequency pulses from the ratio of the two measured... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612543 Tue, 17 Jan 2012 05:00:00 +0100 5612543 http://www.medworm.com/index.php?rid=5600457&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24158 AbstractA novel multislice B1‐mapping method dubbed dual refocusing echo acquisition mode is proposed, able to cover the whole transmit coil volume in only one second, which is more than an order of magnitude faster than established approaches. The dual refocusing echo acquisition mode technique employs a stimulated echo acquisition mode (STEAM) preparation sequence followed by a tailored single‐shot gradient echo sequence, measuring simultaneously the stimulated echo and the free induction decay as gradient‐recalled echoes, and determining the actual flip angle of the STEAM preparation radiofrequency pulses from the ratio of the two measured signals. Due to an elaborated timing scheme, the method is insensitive against susceptibility/chemical shift effects and can deliver a B0 phase... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5600457 Tue, 17 Jan 2012 05:00:00 +0100 5600457 http://www.medworm.com/index.php?rid=5612565&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246567%26dopt%3DAbstract Authors: Qian C, Murphy-Boesch J, Dodd S, Koretsky A Abstract A completely wireless detection coil with an integrated parametric amplifier has been constructed to provide local amplification and transmission of MR signals. The sample coil is one element of a parametric amplifier using a zero-bias diode that mixes the weak MR signal with a strong pump signal that is obtained from an inductively coupled external loop. The NMR sample coil develops current gain via reduction in the effective coil resistance. Higher gain can be obtained by adjusting the level of the pumping power closer to the oscillation threshold, but the gain is ultimately constrained by the bandwidth requirement of MRI experiments. A feasibility study here shows that on a NaCl/D(2) O phantom, (23) Na signals with 20... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612565 Fri, 13 Jan 2012 05:00:00 +0100 5612565 http://www.medworm.com/index.php?rid=5612564&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246646%26dopt%3DAbstract Authors: Auboiroux V, Viallon M, Roland J, Hyacinthe JN, Petrusca L, Morel DR, Goget T, Terraz S, Gross P, Becker CD, Salomir R Abstract MR acoustic radiation force imaging (ARFI) is an elegant adjunct to MR-guided high intensity focused ultrasound for treatment planning and optimization, permitting in situ assessment of the focusing and targeting quality. The thermal effect of high intensity focused ultrasound pulses associated with ARFI measurements is recommended to be monitored on line, in particular when the beam crosses highly absorbent structures or interfaces (e.g., bones or air-filled cavities). A dedicated MR sequence is proposed here, derived from a segmented gradient echo-echo planar imaging kernel by adding a bipolar motion encoding gradient with interleaved alternatin... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612564 Fri, 13 Jan 2012 05:00:00 +0100 5612564 http://www.medworm.com/index.php?rid=5612562&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246655%26dopt%3DAbstract Authors: Varma G, Lenkinski RE, Vinogradov E Abstract The keyhole technique, which involves the acquisition of dynamic data at low resolution in combination with a high-resolution reference, is developed for the purposes of chemical exchange saturation transfer (CEST) imaging, i.e., Keyhole CEST. Low-resolution data are acquired with saturation applied at different frequencies for Z-spectra, along with a high-resolution reference image taken without saturation. Three methods for high-resolution reconstruction of Keyhole CEST are evaluated using the values from quantitative high-resolution CEST maps. In addition, Keyhole CEST is applied for collection of data used for B(0) correction. The keyhole approach is evaluated for CEST contrast generation using exchanging protons in hydroxyl... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612562 Fri, 13 Jan 2012 05:00:00 +0100 5612562 http://www.medworm.com/index.php?rid=5612561&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246669%26dopt%3DAbstract In this study, a novel kinetic model for the signal evolution in such acquisitions is derived and applied to healthy volunteers and to a patient with Moya-Moya disease. The model incorporates bolus dispersion, T(1) decay and radio frequency effects and is applicable to other angiographic methods based on continuous or pseudocontinuous arterial spin labeling. The model fits the data well in all subjects and yields parametric maps relating to blood volume, arrival time, and dispersion, changes to which may indicate disease. These maps are also used to generate synthesized images of blood inflow without bias from T(1) decay and radio frequency effects, greatly improving collateral vessel visibility in the patient with Moya-Moya disease. Relative volume flow rates in downstream vessels are als... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612561 Fri, 13 Jan 2012 05:00:00 +0100 5612561 http://www.medworm.com/index.php?rid=5612560&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246684%26dopt%3DAbstract Authors: Song X, Gilad AA, Joel S, Liu G, Bar-Shir A, Liang Y, Gorelik M, Pekar JJ, van Zijl PC, Bulte JW, McMahon MT Abstract Chemical exchange saturation transfer MRI is a promising new technique for cellular and molecular imaging. This contrast allows the detection of tumors and ischemia without the use of gadolinium as well as the design of microenvironment-sensitive probes that can be discriminated based on their exchange contrast properties and saturation frequency. Current acquisition schemes to detect and analyze this contrast suffer from sensitivity to spatial B(0) inhomogeneity and low contrast-to-noise-ratio, which is an obstacle to widespread adoption of the technology. A new method to detect chemical exchange saturation transfer contrast is proposed here, termed "lengt... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612560 Fri, 13 Jan 2012 05:00:00 +0100 5612560 http://www.medworm.com/index.php?rid=5612559&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246720%26dopt%3DAbstract This article describes a novel technique using a three-dimensional-echo planar imaging navigator, of which the contrast is independent of the b-value, to perform prospective motion correction in diffusion weighted images, without having to reacquire volumes during which motion occurred, unless motion exceeded some preset thresholds. Water phantom and human brain data were acquired using the standard and navigated diffusion sequences, and the mean and whole brain histogram of the fractional anisotropy and mean diffusivity were analyzed. Our results show that adding the navigator does not influence the diffusion sequence. With head motion, the whole brain histogram-fractional anisotropy shows a shift toward lower anisotropy with a significant decrease in both the mean fractional anisotropy a... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612559 Fri, 13 Jan 2012 05:00:00 +0100 5612559 http://www.medworm.com/index.php?rid=5612555&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246786%26dopt%3DAbstract This study shows that a PatLoc system actually has a higher degree of freedom in spatial encoding to mitigate the two challenges mentioned above. Specifically, a PatLoc system can generate not only multipolar but also linear SEMs, which can be used to reduce the loss of spatial resolution at the field-of-view center. Here, we present an efficient and generalized image reconstruction method for PatLoc imaging using multiple SEMs without explicitly identifying the locations where SEM encoding is not unique. Reconstructions using simulations and empirical experimental data are compared with those using conventional linear gradients to demonstrate that the general combination of SEMs can improve image reconstructions. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc. PMID: 22246786 [Pu... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612555 Fri, 13 Jan 2012 05:00:00 +0100 5612555 http://www.medworm.com/index.php?rid=5612553&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246803%26dopt%3DAbstract Authors: Wu B, Zhang X, Wang C, Li Y, Pang Y, Lu J, Xu D, Majumdar S, Nelson SJ, Vigneron DB Abstract A flexible transceiver array, capable of multiple-purpose imaging applications in vivo at ultrahigh magnetic fields was designed, implemented and tested on a 7 T MR scanner. By alternately placing coil elements with primary and secondary harmonics, improved decoupling among coil elements was accomplished without requiring decoupling circuitry between resonant elements, which is commonly required in high-frequency transceiver arrays to achieve sufficient element-isolation during radiofrequency excitation. This flexible array design is capable of maintaining the required decoupling among resonant elements in different array size and geometry and is scalable in coil size and number of... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612553 Fri, 13 Jan 2012 05:00:00 +0100 5612553 http://www.medworm.com/index.php?rid=5612552&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246857%26dopt%3DAbstract This article presents comparison of optimized 3D variable flip angle UTE (VFA-UTE) and 2D saturation recovery UTE (SR-UTE) sequences to quantify T(1) in agar phantoms and human Achilles tendon. Achilles tendon T(1) values for asymptomatic volunteers were compared to Achilles tendon T(1) values calculated from patients with clinical diagnoses of spondyloarthritis (SpA) and Achilles tendinopathy using an optimized VFA-UTE sequence. T(1) values from phantom data for VFA- and SR-UTE compare well against calculated T(1) values from an assumed gold standard inversion recovery spin echo sequence. Mean T(1) values in asymptomatic Achilles tendon were found to be 725 ± 42 ms and 698 ± 54 ms for SR- and VFA-UTE, respectively. The patient group mean T(1) value for Achilles tendon was found to be 95... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612552 Fri, 13 Jan 2012 05:00:00 +0100 5612552 http://www.medworm.com/index.php?rid=5612551&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246917%26dopt%3DAbstract In this study, nonselective DANTE pulse trains are used in combination with gradient pulses and short repetition times as motion-sensitive preparation modules. We show that while the longitudinal magnetization of static tissue is mostly preserved, flowing spins are largely (or fully) attenuated as they fail to establish transverse steady state due to a spoiling effect caused by flow along the applied gradient. The attenuation of flowing spins is effectively insensitive to spin velocity (above a low threshold) and can be approximately quantified with a simple T(1) longitudinal magnetization decay model. The relevant analytical equations for moving spins and static spins during DANTE module application are derived for both transient and steady state epochs. The equations are validated by com... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612551 Fri, 13 Jan 2012 05:00:00 +0100 5612551 http://www.medworm.com/index.php?rid=5612550&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246956%26dopt%3DAbstract B(1) mapping with selective pulses. Magn Reson Med. 2012 Jan 13; Authors: Bouhrara M, Bonny JM Abstract Knowledge of B 1+ distribution is crucial for many applications, such as quantitative MRI. A novel method has been developed to improve the accuracy of the conventionally applied double-angle method for B 1+ mapping. It solves the remaining issues raised by the use of selective pulses for slice selection to accelerate the acquisition process. A general approach for reconstructing B 1+ maps is presented first. It takes B 1+-induced slice profile distortions over off-resonance frequencies into account. It is then shown how the ratio between the prescribed flip angles can be adjusted to reach a compromise between the level of noise propagated onto B 1+ maps and the... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612550 Fri, 13 Jan 2012 05:00:00 +0100 5612550 http://www.medworm.com/index.php?rid=5612549&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246975%26dopt%3DAbstract Authors: Malik SJ, Padormo F, Price AN, Hajnal JV Abstract A spatially resolved extended phase graph (SR-EPG) framework is proposed for prediction of echo amplitudes in the presence of spatially variable radio frequency (RF) fields. The method may be used to examine any regularly repeating pulse sequence and provides a design framework for parallel transmission (PTx) systems; in this work signal homogeneity in static pseudo-steady state (SPSS) turbo spin echo (TSE) imaging was investigated. Building on SR-EPG calculations with PTx, a dynamic RF-shimming approach is proposed in which, RF pulse amplitudes and phases are optimized on a per channel and per pulse basis to yield the desired signal response for all echoes. Results show significant improvements over "static" RF shimming (i... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612549 Fri, 13 Jan 2012 05:00:00 +0100 5612549 http://www.medworm.com/index.php?rid=5612548&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246991%26dopt%3DAbstract Authors: Bieri O, Ganter C, Scheffler K Abstract In general, MR image contrast is expected to be resolution independent, but a pronounced loss of contrast is observed between fluids and tissues with contemporary musculoskeletal protocols (typical inplane resolution << 1 mm) using nonbalanced steady-state free precession, such as double echo steady state. For nonbalanced steady-state free precession, diffusion sensitivity increases with increasing spoiler moments which increase with decreasing voxel size, suggesting diffusion damping as the major cause for the observed contrast variation. This is confirmed by simulations and measurements indicating that for fluids, diffusion effects become apparent already for resolutions Δx < 1 mm, whereas tissues typically require Δx &l... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612548 Fri, 13 Jan 2012 05:00:00 +0100 5612548 http://www.medworm.com/index.php?rid=5612547&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22247007%26dopt%3DAbstract Authors: Shrot S, Anaby D, Krivoy A, Makarovsky I, Rosman Y, Bloch-Shilderman E, Lazar S, Bar-Shir A, Cohen Y Abstract Organophosphates are highly toxic substances, which cause severe brain damage. The hallmark of the brain injury is major convulsions. The goal of this study was to assess the spatial and temporal MR changes in the brain of paraoxon intoxicated rats. T2-weighted MRI and (1) H-MR-spectroscopy were conducted before intoxication, 3 h, 24 h, and 8 days postintoxication. T2 prolongation mainly in the thalami and cortex was evident as early as 3 h after intoxication (4-6% increase in T2 values, P < 0.05). On spectroscopy, N-acetyl aspartate (NAA)/creatine and NAA/choline levels significantly decreased 3 h postintoxication (>20% decrease, P < 0.005), and 3 h lacta... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612547 Fri, 13 Jan 2012 05:00:00 +0100 5612547 http://www.medworm.com/index.php?rid=5612546&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22247024%26dopt%3DAbstract Authors: Karampinos DC, Yu H, Shimakawa A, Link TM, Majumdar S Abstract Chemical shift-based water/fat separation methods have been emerging due to the growing clinical need for fat quantification in different body organs. Accurate quantification of proton-density fat fraction requires the assessment of many confounding factors, including the need of modeling the presence of multiple peaks in the fat spectrum. Most recent quantitative chemical shift-based water/fat separation approaches rely on a multipeak fat spectrum with precalibrated peak locations and precalibrated or self-calibrated peak relative amplitudes. However, water/fat susceptibility differences can induce fat spectrum resonance shifts depending on the shape and orientation of the fatty inclusions. The effect is of pa... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612546 Fri, 13 Jan 2012 05:00:00 +0100 5612546 http://www.medworm.com/index.php?rid=5612545&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22247080%26dopt%3DAbstract In this study, multichannel transmission is used to address the effects that variations in B(0) homogeneity have on fat-saturation preparation through the use of the frequency, phase, and amplitude degrees of freedom afforded by independent transmission channels. B(1) homogeneity is intrinsically included via use of coil sensitivities in calculations. A new method, parallel excitation for B-field insensitive fat-saturation preparation, can achieve fat saturation in 89% of voxels with M(z) ≤ 0.1 in the presence of ±4 ppm B(0) variation, where traditional CHESS methods achieve only 40% in the same conditions. While there has been much progress to apply multichannel transmission at high field strengths, particular focus is given here to application of these methods at 1.5 T. Magn Reson Med... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612545 Fri, 13 Jan 2012 05:00:00 +0100 5612545 http://www.medworm.com/index.php?rid=5586662&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24130 This article presents comparison of optimized 3D variable flip angle UTE (VFA‐UTE) and 2D saturation recovery UTE (SR‐UTE) sequences to quantify T1 in agar phantoms and human Achilles tendon. Achilles tendon T1 values for asymptomatic volunteers were compared to Achilles tendon T1 values calculated from patients with clinical diagnoses of spondyloarthritis (SpA) and Achilles tendinopathy using an optimized VFA‐UTE sequence. T1 values from phantom data for VFA‐ and SR‐UTE compare well against calculated T1 values from an assumed gold standard inversion recovery spin echo sequence. Mean T1 values in asymptomatic Achilles tendon were found to be 725 ± 42 ms and 698 ± 54 ms for SR‐ and VFA‐UTE, respectively. The patient group mean T1 value for Achilles tendon was found to be 95... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586662 Fri, 13 Jan 2012 05:00:00 +0100 5586662 http://www.medworm.com/index.php?rid=5586661&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23311 In this study, a novel kinetic model for the signal evolution in such acquisitions is derived and applied to healthy volunteers and to a patient with Moya‐Moya disease. The model incorporates bolus dispersion, T1 decay and radio frequency effects and is applicable to other angiographic methods based on continuous or pseudocontinuous arterial spin labeling. The model fits the data well in all subjects and yields parametric maps relating to blood volume, arrival time, and dispersion, changes to which may indicate disease. These maps are also used to generate synthesized images of blood inflow without bias from T1 decay and radio frequency effects, greatly improving collateral vessel visibility in the patient with Moya‐Moya disease. Relative volume flow rates in downstream vessels are als... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586661 Fri, 13 Jan 2012 05:00:00 +0100 5586661 http://www.medworm.com/index.php?rid=5586660&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24157 AbstractChemical shift‐based water/fat separation methods have been emerging due to the growing clinical need for fat quantification in different body organs. Accurate quantification of proton‐density fat fraction requires the assessment of many confounding factors, including the need of modeling the presence of multiple peaks in the fat spectrum. Most recent quantitative chemical shift‐based water/fat separation approaches rely on a multipeak fat spectrum with precalibrated peak locations and precalibrated or self‐calibrated peak relative amplitudes. However, water/fat susceptibility differences can induce fat spectrum resonance shifts depending on the shape and orientation of the fatty inclusions. The effect is of particular interest in the skeletal muscle due to the anisotropic ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586660 Fri, 13 Jan 2012 05:00:00 +0100 5586660 http://www.medworm.com/index.php?rid=5586659&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24153 AbstractA spatially resolved extended phase graph (SR‐EPG) framework is proposed for prediction of echo amplitudes in the presence of spatially variable radio frequency (RF) fields. The method may be used to examine any regularly repeating pulse sequence and provides a design framework for parallel transmission (PTx) systems; in this work signal homogeneity in static pseudo‐steady state (SPSS) turbo spin echo (TSE) imaging was investigated. Building on SR‐EPG calculations with PTx, a dynamic RF‐shimming approach is proposed in which, RF pulse amplitudes and phases are optimized on a per channel and per pulse basis to yield the desired signal response for all echoes. Results show significant improvements over “static” RF shimming (in which the relative amplitude/phase of the PTx... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586659 Fri, 13 Jan 2012 05:00:00 +0100 5586659 http://www.medworm.com/index.php?rid=5586658&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24146 AbstractKnowledge of B distribution is crucial for many applications, such as quantitative MRI. A novel method has been developed to improve the accuracy of the conventionally applied double‐angle method for B mapping. It solves the remaining issues raised by the use of selective pulses for slice selection to accelerate the acquisition process. A general approach for reconstructing B maps is presented first. It takes B‐induced slice profile distortions over off‐resonance frequencies into account. It is then shown how the ratio between the prescribed flip angles can be adjusted to reach a compromise between the level of noise propagated onto B maps and the width of the range in which the field can be mapped. Lastly, several solutions are proposed for reducing the B‐dependent polluti... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586658 Fri, 13 Jan 2012 05:00:00 +0100 5586658 http://www.medworm.com/index.php?rid=5586657&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24142 In this study, nonselective DANTE pulse trains are used in combination with gradient pulses and short repetition times as motion‐sensitive preparation modules. We show that while the longitudinal magnetization of static tissue is mostly preserved, flowing spins are largely (or fully) attenuated as they fail to establish transverse steady state due to a spoiling effect caused by flow along the applied gradient. The attenuation of flowing spins is effectively insensitive to spin velocity (above a low threshold) and can be approximately quantified with a simple T1 longitudinal magnetization decay model. The relevant analytical equations for moving spins and static spins during DANTE module application are derived for both transient and steady state epochs. The equations are validated by com... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586657 Fri, 13 Jan 2012 05:00:00 +0100 5586657 http://www.medworm.com/index.php?rid=5586656&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24121 AbstractA flexible transceiver array, capable of multiple‐purpose imaging applications in vivo at ultrahigh magnetic fields was designed, implemented and tested on a 7 T MR scanner. By alternately placing coil elements with primary and secondary harmonics, improved decoupling among coil elements was accomplished without requiring decoupling circuitry between resonant elements, which is commonly required in high‐frequency transceiver arrays to achieve sufficient element‐isolation during radiofrequency excitation. This flexible array design is capable of maintaining the required decoupling among resonant elements in different array size and geometry and is scalable in coil size and number of resonant elements (i.e., number of channels), yielding improved filling factors for various bod... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586656 Fri, 13 Jan 2012 05:00:00 +0100 5586656 http://www.medworm.com/index.php?rid=5586655&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23310 AbstractThe keyhole technique, which involves the acquisition of dynamic data at low resolution in combination with a high‐resolution reference, is developed for the purposes of chemical exchange saturation transfer (CEST) imaging, i.e., Keyhole CEST. Low‐resolution data are acquired with saturation applied at different frequencies for Z‐spectra, along with a high‐resolution reference image taken without saturation. Three methods for high‐resolution reconstruction of Keyhole CEST are evaluated using the values from quantitative high‐resolution CEST maps. In addition, Keyhole CEST is applied for collection of data used for B0 correction. The keyhole approach is evaluated for CEST contrast generation using exchanging protons in hydroxyl groups. First, the techniques are evaluated... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586655 Fri, 13 Jan 2012 05:00:00 +0100 5586655 http://www.medworm.com/index.php?rid=5586654&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23274 AbstractA completely wireless detection coil with an integrated parametric amplifier has been constructed to provide local amplification and transmission of MR signals. The sample coil is one element of a parametric amplifier using a zero‐bias diode that mixes the weak MR signal with a strong pump signal that is obtained from an inductively coupled external loop. The NMR sample coil develops current gain via reduction in the effective coil resistance. Higher gain can be obtained by adjusting the level of the pumping power closer to the oscillation threshold, but the gain is ultimately constrained by the bandwidth requirement of MRI experiments. A feasibility study here shows that on a NaCl/D2O phantom, 23Na signals with 20 dB of gain can be readily obtained with a concomitant bandwidth o... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586654 Fri, 13 Jan 2012 05:00:00 +0100 5586654 http://www.medworm.com/index.php?rid=5586653&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24155 AbstractOrganophosphates are highly toxic substances, which cause severe brain damage. The hallmark of the brain injury is major convulsions. The goal of this study was to assess the spatial and temporal MR changes in the brain of paraoxon intoxicated rats. T2‐weighted MRI and 1H‐MR‐spectroscopy were conducted before intoxication, 3 h, 24 h, and 8 days postintoxication. T2 prolongation mainly in the thalami and cortex was evident as early as 3 h after intoxication (4–6% increase in T2 values, P < 0.05). On spectroscopy,N‐acetyl aspartate (NAA)/creatine and NAA/choline levels significantly decreased 3 h postintoxication (>20% decrease, P < 0.005), and 3 h lactate peak was evident in all intoxicated animals. On the 8th day, although very little T2 changes were evident, NAA... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586653 Fri, 13 Jan 2012 05:00:00 +0100 5586653 http://www.medworm.com/index.php?rid=5586652&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24154 AbstractIn general, MR image contrast is expected to be resolution independent, but a pronounced loss of contrast is observed between fluids and tissues with contemporary musculoskeletal protocols (typical inplane resolution << 1 mm) using nonbalanced steady‐state free precession, such as double echo steady state. For nonbalanced steady‐state free precession, diffusion sensitivity increases with increasing spoiler moments which increase with decreasing voxel size, suggesting diffusion damping as the major cause for the observed contrast variation. This is confirmed by simulations and measurements indicating that for fluids, diffusion effects become apparent already for resolutions Δx < 1 mm, whereas tissues typically require Δx < 200 μm. Gradient spoiling, however, is ge... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586652 Fri, 13 Jan 2012 05:00:00 +0100 5586652 http://www.medworm.com/index.php?rid=5586651&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24115 This study shows that a PatLoc system actually has a higher degree of freedom in spatial encoding to mitigate the two challenges mentioned above. Specifically, a PatLoc system can generate not only multipolar but also linear SEMs, which can be used to reduce the loss of spatial resolution at the field‐of‐view center. Here, we present an efficient and generalized image reconstruction method for PatLoc imaging using multiple SEMs without explicitly identifying the locations where SEM encoding is not unique. Reconstructions using simulations and empirical experimental data are compared with those using conventional linear gradients to demonstrate that the general combination of SEMs can improve image reconstructions. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc. (Source: Magnetic ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586651 Fri, 13 Jan 2012 05:00:00 +0100 5586651 http://www.medworm.com/index.php?rid=5586650&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23314 This article describes a novel technique using a three‐dimensional‐echo planar imaging navigator, of which the contrast is independent of the b‐value, to perform prospective motion correction in diffusion weighted images, without having to reacquire volumes during which motion occurred, unless motion exceeded some preset thresholds. Water phantom and human brain data were acquired using the standard and navigated diffusion sequences, and the mean and whole brain histogram of the fractional anisotropy and mean diffusivity were analyzed. Our results show that adding the navigator does not influence the diffusion sequence. With head motion, the whole brain histogram‐fractional anisotropy shows a shift toward lower anisotropy with a significant decrease in both the mean fractional anis... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586650 Fri, 13 Jan 2012 05:00:00 +0100 5586650 http://www.medworm.com/index.php?rid=5586649&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23312 AbstractChemical exchange saturation transfer MRI is a promising new technique for cellular and molecular imaging. This contrast allows the detection of tumors and ischemia without the use of gadolinium as well as the design of microenvironment‐sensitive probes that can be discriminated based on their exchange contrast properties and saturation frequency. Current acquisition schemes to detect and analyze this contrast suffer from sensitivity to spatial B0 inhomogeneity and low contrast‐to‐noise‐ratio, which is an obstacle to widespread adoption of the technology. A new method to detect chemical exchange saturation transfer contrast is proposed here, termed “length and offset varied saturation” which acquires a set of images with the saturation parameters varied so as to modulat... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586649 Fri, 13 Jan 2012 05:00:00 +0100 5586649 http://www.medworm.com/index.php?rid=5586648&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23309 AbstractMR acoustic radiation force imaging (ARFI) is an elegant adjunct to MR‐guided high intensity focused ultrasound for treatment planning and optimization, permitting in situ assessment of the focusing and targeting quality. The thermal effect of high intensity focused ultrasound pulses associated with ARFI measurements is recommended to be monitored on line, in particular when the beam crosses highly absorbent structures or interfaces (e.g., bones or air‐filled cavities). A dedicated MR sequence is proposed here, derived from a segmented gradient echo‐echo planar imaging kernel by adding a bipolar motion encoding gradient with interleaved alternating polarities. Temporal resolution was reduced to 2.1 s, with in‐plane spatial resolution of 1 mm. MR‐ARFI measurements were exe... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586648 Fri, 13 Jan 2012 05:00:00 +0100 5586648 http://www.medworm.com/index.php?rid=5589875&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22234983%26dopt%3DAbstract Authors: Odille F, Menys A, Ahmed A, Punwani S, Taylor SA, Atkinson D Abstract Evaluation of small bowel motility from two-dimensional dynamic MRI is of increasing interest for the assessment of segmental diseases such as Crohn's disease. We propose to use nonrigid image registration for automated motility analysis. Registration is particularly difficult when localized intensity changes occur (e.g., due to intraluminal flow or through-plane motion). Therefore, displacements were extracted using a joint registration and modeling of intensity changes. Results were analyzed in 10 patients with known or suspected Crohn's disease. Bowel wall displacements were assessed by tracking bowel cross-sectional markers over time. Automated tracking with the proposed technique was in good agreeme... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5589875 Tue, 10 Jan 2012 05:00:00 +0100 5589875 http://www.medworm.com/index.php?rid=5586663&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23298 AbstractEvaluation of small bowel motility from two‐dimensional dynamic MRI is of increasing interest for the assessment of segmental diseases such as Crohn's disease. We propose to use nonrigid image registration for automated motility analysis. Registration is particularly difficult when localized intensity changes occur (e.g., due to intraluminal flow or through‐plane motion). Therefore, displacements were extracted using a joint registration and modeling of intensity changes. Results were analyzed in 10 patients with known or suspected Crohn's disease. Bowel wall displacements were assessed by tracking bowel cross‐sectional markers over time. Automated tracking with the proposed technique was in good agreement with manual tracking (similar bias, improved standard deviations). The... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586663 Tue, 10 Jan 2012 05:00:00 +0100 5586663 http://www.medworm.com/index.php?rid=5589882&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22231619%26dopt%3DAbstract Authors: Khanna A, Branca RT Abstract The recent discovery of active brown adipose tissue (BAT) in adult humans and the correlation found between the activity of this tissue and resting metabolic rate strongly suggest that this tissue may be implicated in the development of obesity in humans, as it is in rodents. Despite the possible physiological role of this tissue in the onset of human obesity, few noninvasive imaging techniques to detect BAT activity in humans exist. The scope of this work is to investigate the possibility of detecting BAT activity using blood-oxygen-level-dependent MRI. Our results show that the strong increase in oxygen consumption and consequent increase in blood deoxyhemoglobin levels following BAT activation lead to a well-localized signal drop in BAT. Thi... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5589882 Mon, 09 Jan 2012 05:00:00 +0100 5589882 http://www.medworm.com/index.php?rid=5589881&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22231647%26dopt%3DAbstract In this study, a novel and comprehensive SAR prediction concept for parallel radiofrequency transmission MRI is presented, based on precalculated magnetic and electric fields obtained from electromagnetic simulations of numerical body models. The application of so-called Q-matrices and further computational optimizations allow for a real-time estimation of the SAR prior to scanning. This SAR estimation method was fully integrated into an eight-channel whole body MRI system, and it facilitated the selection of different body models and body positions. Experimental validation of the global SAR in phantoms demonstrated a good qualitative and quantitative agreement with the predictions. An initial in vivo validation showed good qualitative agreement between simulated and measured amplitude of ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5589881 Mon, 09 Jan 2012 05:00:00 +0100 5589881 http://www.medworm.com/index.php?rid=5589880&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22231672%26dopt%3DAbstract We present a new intervention-based phase unwrapping algorithm, which solves the inherent integration-path-dependent problem (typically resulting in streaks), by using a 2D recursive orthogonal referring (PUROR) approach. The streaks were removed by three consecutive procedures: intra-image phase unwrapping, inter-image cross-referring a "good-strip," and cross-referring line segments. The application of these procedures results in streak-free 2D phase images. The phase inconsistencies across slices in a 3D image were removed using a hybrid 3D PUROR algorithm: the two step approach involves stacking the individual slices, by using the mean phase values of each slice, then applying the 2D PUROR algorithm to reformatted 2D images that include the slice direction. The described approach was t... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5589880 Mon, 09 Jan 2012 05:00:00 +0100 5589880 http://www.medworm.com/index.php?rid=5589879&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22231729%26dopt%3DAbstract Authors: Mamata H, Tokuda J, Gill RR, Padera RF, Lenkinski RE, Sugarbaker DJ, Butler JP, Hatabu H Abstract The purpose of this study is to evaluate perfusion indices and pharmacokinetic parameters in solitary pulmonary nodules (SPNs). Thirty patients of 34 enrolled with SPNs (15-30 mm) were evaluated in this study. T1 and T2-weighted structural images and 2D turbo FLASH perfusion images were acquired with shallow free breathing. B-spline nonrigid image registration and optimization by χ(2) test against pharmacokinetic model curve were performed on dynamic contrast-enhanced MRI. This allowed voxel-by-voxel calculation of k(ep) , the rate constant for tracer transport to and from plasma and the extravascular extracellular space. Mean transit time, time-to-peak, initial slope, and ma... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5589879 Mon, 09 Jan 2012 05:00:00 +0100 5589879 http://www.medworm.com/index.php?rid=5589878&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22231781%26dopt%3DAbstract Authors: Couch MJ, Ouriadov A, Santyr GE Abstract Lung ventilation was mapped in seven healthy male Sprague-Dawley rats (433 ± 24 g) using hyperpolarized (129) Xe magnetic resonance imaging (MRI) at 3.0 T, and validated with hyperpolarized (3) He MRI under similar ventilator conditions. Ventilation maps were obtained using flip angle variation for offset of RF and relaxation (FAVOR) which is a multiple breath imaging technique that extracts the fractional ventilation parameter, r, on a pixel-by-pixel basis from the dynamic signal enhancement. r is defined as the fractional refreshment of gas per breath. Under the ventilator conditions used in this work, whole-lung measurements of fractional ventilation obtained using hyperpolarized (129) Xe were not significantly different from th... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5589878 Mon, 09 Jan 2012 05:00:00 +0100 5589878 http://www.medworm.com/index.php?rid=5589877&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22231859%26dopt%3DAbstract Authors: Heidemann RM, Ivanov D, Trampel R, Fasano F, Meyer H, Pfeuffer J, Turner R Abstract Echo-planar imaging is the most widely used imaging sequence for functional magnetic resonance imaging (fMRI) due to its fast acquisition. However, it is prone to local distortions, image blurring, and signal voids. As these effects scale with echo train length and field strength, it is essential for high-resolution echo-planar imaging at ultrahigh field to address these problems. Partially parallel acquisition methods can be used to improve the image quality of echo-planar imaging. However, partially parallel acquisition can be affected by aliasing artifacts and noise enhancement. Another way to shorten the echo train length is to reduce the field-of-view (FOV) while maintaining the same s... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5589877 Mon, 09 Jan 2012 05:00:00 +0100 5589877 http://www.medworm.com/index.php?rid=5586669&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24140 We present a new intervention‐based phase unwrapping algorithm, which solves the inherent integration‐path‐dependent problem (typically resulting in streaks), by using a 2D recursive orthogonal referring (PUROR) approach. The streaks were removed by three consecutive procedures: intra‐image phase unwrapping, inter‐image cross‐referring a “good‐strip,” and cross‐referring line segments. The application of these procedures results in streak‐free 2D phase images. The phase inconsistencies across slices in a 3D image were removed using a hybrid 3D PUROR algorithm: the two step approach involves stacking the individual slices, by using the mean phase values of each slice, then applying the 2D PUROR algorithm to reformatted 2D images that include the slice direction. The de... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586669 Mon, 09 Jan 2012 05:00:00 +0100 5586669 http://www.medworm.com/index.php?rid=5586668&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24118 AbstractThe recent discovery of active brown adipose tissue (BAT) in adult humans and the correlation found between the activity of this tissue and resting metabolic rate strongly suggest that this tissue may be implicated in the development of obesity in humans, as it is in rodents. Despite the possible physiological role of this tissue in the onset of human obesity, few noninvasive imaging techniques to detect BAT activity in humans exist. The scope of this work is to investigate the possibility of detecting BAT activity using blood‐oxygen‐level‐dependent MRI. Our results show that the strong increase in oxygen consumption and consequent increase in blood deoxyhemoglobin levels following BAT activation lead to a well‐localized signal drop in BAT. This strongly suggests the possib... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586668 Mon, 09 Jan 2012 05:00:00 +0100 5586668 http://www.medworm.com/index.php?rid=5586667&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24156 AbstractEcho‐planar imaging is the most widely used imaging sequence for functional magnetic resonance imaging (fMRI) due to its fast acquisition. However, it is prone to local distortions, image blurring, and signal voids. As these effects scale with echo train length and field strength, it is essential for high‐resolution echo‐planar imaging at ultrahigh field to address these problems. Partially parallel acquisition methods can be used to improve the image quality of echo‐planar imaging. However, partially parallel acquisition can be affected by aliasing artifacts and noise enhancement. Another way to shorten the echo train length is to reduce the field‐of‐view (FOV) while maintaining the same spatial resolution. However, to achieve significant acceleration, the resulting FO... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586667 Mon, 09 Jan 2012 05:00:00 +0100 5586667 http://www.medworm.com/index.php?rid=5586666&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24138 In this study, a novel and comprehensive SAR prediction concept for parallel radiofrequency transmission MRI is presented, based on precalculated magnetic and electric fields obtained from electromagnetic simulations of numerical body models. The application of so‐called Q‐matrices and further computational optimizations allow for a real‐time estimation of the SAR prior to scanning. This SAR estimation method was fully integrated into an eight‐channel whole body MRI system, and it facilitated the selection of different body models and body positions. Experimental validation of the global SAR in phantoms demonstrated a good qualitative and quantitative agreement with the predictions. An initial in vivo validation showed good qualitative agreement between simulated and measured ampli... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586666 Mon, 09 Jan 2012 05:00:00 +0100 5586666 http://www.medworm.com/index.php?rid=5586665&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24152 AbstractLung ventilation was mapped in seven healthy male Sprague‐Dawley rats (433 ± 24 g) using hyperpolarized 129Xe magnetic resonance imaging (MRI) at 3.0 T, and validated with hyperpolarized 3He MRI under similar ventilator conditions. Ventilation maps were obtained using flip angle variation for offset of RF and relaxation (FAVOR) which is a multiple breath imaging technique that extracts the fractional ventilation parameter, r, on a pixel‐by‐pixel basis from the dynamic signal enhancement. r is defined as the fractional refreshment of gas per breath. Under the ventilator conditions used in this work, whole‐lung measurements of fractional ventilation obtained using hyperpolarized 129Xe were not significantly different from those obtained using hyperpolarized 3He (p = 0.8125 b... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586665 Mon, 09 Jan 2012 05:00:00 +0100 5586665 http://www.medworm.com/index.php?rid=5586664&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24150 AbstractThe purpose of this study is to evaluate perfusion indices and pharmacokinetic parameters in solitary pulmonary nodules (SPNs). Thirty patients of 34 enrolled with SPNs (15–30 mm) were evaluated in this study. T1 and T2‐weighted structural images and 2D turbo FLASH perfusion images were acquired with shallow free breathing. B‐spline nonrigid image registration and optimization by χ2 test against pharmacokinetic model curve were performed on dynamic contrast‐enhanced MRI. This allowed voxel‐by‐voxel calculation of kep, the rate constant for tracer transport to and from plasma and the extravascular extracellular space. Mean transit time, time‐to‐peak, initial slope, and maximum enhancement (Emax) were calculated from time–intensity curves fitted to a gamma variate ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586664 Mon, 09 Jan 2012 05:00:00 +0100 5586664 http://www.medworm.com/index.php?rid=5589876&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22234782%26dopt%3DAbstract This article introduces a new method, referred to as Optimized PCASL (OptPCASL), that minimizes the phase tracking error by applying an additional compensation RF phase term and in-plane gradients to the PCASL pulse train. The optimal RF phase and gradient amplitudes are determined using a prescan procedure, which consists of a series of short scans interleaved with automated postprocessing routines integrated to the scanner console. The prescan procedure is shown to minimize the phase tracking error in a robust and time efficient manner. As an example of its application, the use of OptPCASL for the improved detection of functional activation in the visual cortex is demonstrated and temporal signal-to-noise ratio (SNR), image SNR, and baseline cerebral blood flow measures are compared to t... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5589876 Tue, 03 Jan 2012 05:00:00 +0100 5589876 http://www.medworm.com/index.php?rid=5563290&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24132 AbstractThe purpose of this work was to evaluate a previously proposed approach that aims to improve the point spread function (PSF) of MR spectroscopic imaging (MRSI) to avoid corruption by lipid signal arising from neighboring voxels. Retrospective spatial filtering can be used to alter the PSF; however, this either reduces spatial resolution or requires extending the acquisition in k‐space at the cost of increased imaging time. Alternatively, the method evaluated here, PSF‐choice, can modify the PSF localization to reduce the contamination from adjacent lipids by conforming the signal response more closely to the desired MRSI voxel grid. This is done without increasing scan time or degrading SNR of important metabolites. PSF‐choice achieves improvements in spatial localization thr... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563290 Tue, 03 Jan 2012 05:00:00 +0100 5563290 http://www.medworm.com/index.php?rid=5563289&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24135 This study demonstrates the dependence of non‐local susceptibility effects on object orientation in gradient echo MRI and the reduction of non‐local effects by deconvolution using quantitative susceptibility mapping. Imaging experiments were performed on a 3T MRI system using a spoiled 3D multi‐echo GRE sequence on phantoms of known susceptibilities, and on human brains of healthy subjects and patients with intracerebral hemorrhages. Magnetic field measurements were determined from multiple echo phase data. To determine the quantitative susceptibility mapping, these field measurements were deconvolved through a dipole inversion kernel under a constraint of consistency with the magnitude images. Phantom and human data demonstrated that the hypointense region in GRE magnitude image cor... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563289 Tue, 03 Jan 2012 05:00:00 +0100 5563289 http://www.medworm.com/index.php?rid=5563288&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24136 AbstractThe aim of this study was to investigate T in the Achilles tendon (AT), in vivo, using a three‐dimensional ultrashort time echo (3D‐UTE) sequence, to compare field strength differences (3 and 7 T) and to evaluate a regional variation of T in healthy and pathologic tendon. Ten volunteers with no history of pain in the AT and five patients with chronic Achilles tendinopathy were recruited. 3D‐UTE images were measured with the following echo times, at echo time = [0.07, 0.2, 0.33, 0.46, 0.59, 0.74, 1.0, 1.5, 2.0, 4.0, 6.0, and 9.0 ms]. T values in the AT were calculated by fitting the signal decay to biexponential function. Comparing volunteers between 3 and 7 T, short component T was 0.71 ± 0.17 ms and 0.34 ± 0.09 ms (P < 0.05); bulk long component T was 12.85 ± 1.87 ms a... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563288 Tue, 03 Jan 2012 05:00:00 +0100 5563288 http://www.medworm.com/index.php?rid=5563287&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24137 AbstractA modified Look–Locker acquisition using saturation recovery (MLLSR) for breath‐held myocardial T1 mapping is presented. Despite its reduced dynamic range, saturation recovery enables substantially higher imaging efficiency than conventional inversion recovery T1 mapping because it does not require time for magnetization to relax to equilibrium. Therefore, MLLSR enables segmented readouts, shorter data acquisition windows, and shorter breath holds compared with inversion recovery. T1 measurements in phantoms using MLLSR showed a high correlation with conventional single‐point inversion recovery spin echo. In vivo T1 measurements from normal and infarcted myocardium in 41 volunteers and patients were consistent with previously reported values. Twenty subjects were also scanned... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563287 Tue, 03 Jan 2012 05:00:00 +0100 5563287 http://www.medworm.com/index.php?rid=5563286&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24139 In this study, utility of two motion‐compensation strategies—(i) navigator gating with prospective slice correction and (ii) nonrigid registration—was investigated for myocardial T2 mapping in short axis and horizontal long axis views. Navigator gating provides respiratory motion compensation, whereas registration corrects for residual cardiac and respiratory motion between images; thus, the two strategies provided complementary functions. When these were combined, respiratory‐motion‐induced T2 variability, as measured by both standard deviation and interquartile range, was comparable to that in breath‐hold T2 maps. In normal subjects, this combined motion‐compensation strategy increased the percentage of myocardium with T2 measured to be within normal range from 60.1% to 92.... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563286 Tue, 03 Jan 2012 05:00:00 +0100 5563286 http://www.medworm.com/index.php?rid=5563285&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23252 AbstractA new dual temporal resolution‐based, high spatial resolution, pharmacokinetic parametric mapping method is described ‐ improved coverage and spatial resolution using dual injection dynamic contrast‐enhanced (ICE‐DICE) MRI. In a dual‐bolus dynamic contrast‐enhanced‐MRI acquisition protocol, a high temporal resolution prebolus is followed by a high spatial resolution main bolus to allow high spatial resolution parametric mapping for cerebral tumors. The measured plasma concentration curves from the dual‐bolus data were used to reconstruct a high temporal resolution arterial input function. The new method reduces errors resulting from uncertainty in the temporal alignment of the arterial input function, tissue response function, and sampling grid. The technique provid... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563285 Tue, 03 Jan 2012 05:00:00 +0100 5563285 http://www.medworm.com/index.php?rid=5563284&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24113 This article introduces a new method, referred to as Optimized PCASL (OptPCASL), that minimizes the phase tracking error by applying an additional compensation RF phase term and in‐plane gradients to the PCASL pulse train. The optimal RF phase and gradient amplitudes are determined using a prescan procedure, which consists of a series of short scans interleaved with automated postprocessing routines integrated to the scanner console. The prescan procedure is shown to minimize the phase tracking error in a robust and time efficient manner. As an example of its application, the use of OptPCASL for the improved detection of functional activation in the visual cortex is demonstrated and temporal signal‐to‐noise ratio (SNR) image SNR, and baseline cerebral blood flow measures are compared... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563284 Tue, 03 Jan 2012 05:00:00 +0100 5563284 http://www.medworm.com/index.php?rid=5563283&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24120 AbstractConcomitant gradient fields are transverse magnetic field components that are necessarily present to satisfy Maxwell's equations when magnetic field gradients are utilized in magnetic resonance imaging. They can have deleterious effects that are more prominent at lower static fields and/or higher gradient strengths. In diffusion tensor imaging schemes that employ large gradients that are not symmetric about a refocusing radiofrequency pulse (unlike Stejskal–Tanner, which is symmetric), concomitant fields may cause phase accrual that could corrupt the diffusion measurement. Theory predicting the error from this dephasing is described and experimentally validated for both Reese twice‐refocused and split gradient single spin‐echo diffusion gradient schemes. Bias in apparent diff... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563283 Tue, 03 Jan 2012 05:00:00 +0100 5563283 http://www.medworm.com/index.php?rid=5563282&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24119 AbstractInhomogeneities of the main magnetic field cause geometric distortion in echo‐planar imaging, a method central to functional MRI. A number of correction methods have been proposed, most of which are based on the acquisition of a fieldmap providing the local offsets to the main magnetic field. Here, accelerated multiecho echo‐planar imaging is used, with echo times short enough to enable the construction of a fieldmap of comparable quality from the data themselves. This way, each volume in a time series can be unwarped using a fieldmap obtained from that volume, avoiding volume‐to‐volume field‐motion interactions that invalidate reference data in conventional approaches that use a single, static, fieldmap. The combination of accelerated acquisition with dynamic distortion ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563282 Tue, 03 Jan 2012 05:00:00 +0100 5563282 http://www.medworm.com/index.php?rid=5563281&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24129 AbstractSubject motion during brain magnetic resonance spectroscopy acquisitions generally reduces the magnetic field (B0) homogeneity across the volume of interest or voxel. This is the case even if prospective motion correction ensures that the voxel follows the head. We introduce a novel method for rapidly mapping linear variations in B0 across a small volume using two‐dimensional excitations. The new field mapping technique was integrated into a prospectively motion‐corrected single‐voxel 1H magnetic resonance spectroscopy sequence. Interference with the magnetic resonance spectroscopy measurement was negligible, and there was no penalty in scan time. Frequency shifts were also measured continuously, and both frequency and first‐order shim corrections were applied in real time.... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563281 Tue, 03 Jan 2012 05:00:00 +0100 5563281 http://www.medworm.com/index.php?rid=5612541&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24143 We describe and evaluate a robust method for compressive sensing MRI reconstruction using an iterative soft thresholding framework that is data‐driven, so that no tuning of free parameters is required. The approach described here combines a Nesterov type optimal gradient scheme for iterative update along with standard wavelet‐based adaptive denoising methods, resulting in a leaner implementation compared with the nonlinear conjugate gradient method. Tests with T2 weighted brain data and vascular 3D phase contrast data show that the image quality of reconstructions is comparable with those from an empirically tuned nonlinear conjugate gradient approach. Statistical analysis of image quality scores for multiple datasets indicates that the iterative soft thresholding approach as presented... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5612541 Sun, 01 Jan 2012 05:00:00 +0100 5612541 http://www.medworm.com/index.php?rid=5600456&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24141 AbstractWhite matter is composed primarily of myelinated axons which form fibrous, organized structures and can act as waveguides for the anisotropic propagation of sound. The evaluation of their elastic properties requires both knowledge of the orientation of these waveguides in space, as well as knowledge of the waves propagating along and through them. Here, we present waveguide elastography for the evaluation of the elastic properties of white matter tracts in the human brain, in vivo, using a fusion of diffusion tensor imaging, magnetic resonance elastography, spatial‐spectral filtering, a Helmholtz decomposition, and anisotropic inversions, and apply this method to evaluate the material parameters of the corticospinal tracts of five healthy human volunteers. We begin with an Orthot... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5600456 Sun, 01 Jan 2012 05:00:00 +0100 5600456 http://www.medworm.com/index.php?rid=5586647&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23238 In this study, multichannel transmission is used to address the effects that variations in B0 homogeneity have on fat‐saturation preparation through the use of the frequency, phase, and amplitude degrees of freedom afforded by independent transmission channels. B1 homogeneity is intrinsically included via use of coil sensitivities in calculations. A new method, parallel excitation for B‐field insensitive fat‐saturation preparation, can achieve fat saturation in 89% of voxels with Mz ≤ 0.1 in the presence of ±4 ppm B0 variation, where traditional CHESS methods achieve only 40% in the same conditions. While there has been much progress to apply multichannel transmission at high field strengths, particular focus is given here to application of these methods at 1.5 T. Magn Reson Med, ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5586647 Sun, 01 Jan 2012 05:00:00 +0100 5586647 http://www.medworm.com/index.php?rid=5563280&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24128 The objective of this study was to develop a signal‐to‐noise ratio efficient 3D T2prep spiral gradient echo (3D SPIRAL) sequence for full brain T2 relaxometry and to validate this sequence using 3D multiecho spin echo as reference standard in healthy brains at 1.5 T. 3D SPIRAL was found to provide similar myelin water fraction in six selected white and gray matter areas using region‐of‐interest signal averaging analysis (N = 7, P > 0.05). While 3D multiecho spin echo only provided partial brain coverage, 3D SPIRAL enabled whole brain coverage with a fivefold higher acquisition speed per imaging slice and similar signal‐to‐noise ratio efficiency. Both 3D sequences provided superior signal‐to‐noise ratio efficiency when compared to the conventional 2D multiecho spin echo a... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5563280 Sun, 01 Jan 2012 05:00:00 +0100 5563280 http://www.medworm.com/index.php?rid=5554146&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23192 AbstractThe high molecular weight and low concentration of brain glycogen render its noninvasive quantification challenging. Therefore, the precision increase of the quantification by localized 13C MR at 9.4 to 14.1 T was investigated. Signal‐to‐noise ratio increased by 66%, slightly offset by a T1 increase of 332 ± 15 to 521 ± 34 ms. Isotopic enrichment after long‐term 13C administration was comparable (∼40%) as was the nominal linewidth of glycogen C1 (∼50 Hz). Among the factors that contributed to the 66% observed increase in signal‐to‐noise ratio, the T1 relaxation time impacted the effective signal‐to‐noise ratio by only 10% at a repetition time = 1 s. The signal‐to‐noise ratio increase together with the larger spectral dispersion at 14.1 T resulted in a better... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5554146 Sun, 01 Jan 2012 05:00:00 +0100 5554146 http://www.medworm.com/index.php?rid=5554147&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23278 AbstractIn high‐field MRI, RF flip angle inhomogeneity due to wavelength effects can lead to spatial variations in contrast and sensitivity. Improved flip angle homogeneity can be achieved through multidimensional excitation, but long RF pulse durations limit practical application. A recent approach to reduce RF pulse duration is based on parallel excitation through multiple RF channels. Here, an alternative approach to shorten multidimensional excitation is proposed that makes use of nonlinear spatial variations in the stationary (B0) magnetic field during a B0‐sensitive excitation pulse. As initial demonstration, the method was applied to 2D gradient echo (GE) MRI of human brain at 7 T. Using B0 shims with up to second‐order spatial dependence, it is demonstrated that root‐mean�... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5554147 Thu, 29 Dec 2011 05:00:00 +0100 5554147 http://www.medworm.com/index.php?rid=5546489&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24125 AbstractThe conventional Fourier‐transform‐based spin‐echo sequence with a view angle tilting gradient during data acquisition can correct the in‐plane distortion induced by a chemical shift or B0 field inhomogeneity. However, when extended for 3D applications, alternate k‐space sampling can be beneficial for reducing the lengthy scan time. As spiral trajectories have high k‐space acquisition efficiency, we investigated the applicability of spiral trajectory on a spin‐echo view angle tilting pulse sequence. Computer simulations and phantom and in vivo experiments were performed to validate the usage of spiral readout gradients in the presence of a view angle tilting gradient. The results show that as long as the readout time is comparable to Cartesian readout, the resulting i... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546489 Thu, 29 Dec 2011 00:20:04 +0100 5546489 http://www.medworm.com/index.php?rid=5546519&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23321 In conclusion, the novel application of 1H‐[13C] magnetic resonance spectroscopy in combination with the oral administration of 13C‐labeled lipids is applicable for the longitudinal assessment of in vivo lipid partitioning between multiple tissues. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc. (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546519 Wed, 28 Dec 2011 05:00:00 +0100 5546519 http://www.medworm.com/index.php?rid=5546518&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23320 AbstractGeometric distortion caused by field inhomogeneity along the phase‐encode direction is one of the most prominent artifacts due to a relatively low effective bandwidth along that direction in magnetic resonance echo planar imaging. This work describes a method for correcting in‐plane image distortion along the phase‐encode direction using a view angle tilting imaging technique in spin‐echo echo planar imaging. Spin‐echo echo planar imaging with view angle tilting uses the addition of gradient blips along the slice‐select direction, concurrently applied with the phase‐encode gradient blips, producing an additional phase. This phase effectively offsets an unwanted phase accumulation caused by field inhomogeneity, resulting in the removal of image distortion along the pha... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546518 Wed, 28 Dec 2011 05:00:00 +0100 5546518 http://www.medworm.com/index.php?rid=5546517&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23221 We report on the initial results of using simulated annealing to find optimal sequences for two applications of multiple‐pulse repetition time balanced steady‐state free precession: positive contrast imaging and fat suppression. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc. (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546517 Wed, 28 Dec 2011 05:00:00 +0100 5546517 http://www.medworm.com/index.php?rid=5546516&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23219 In this study, the additional gradients are adjusted in such a way that an elliptical labeling spot is formed, which can be applied to label the blood in multiple vessels simultaneously in conjunction with an increased labeling efficiency compared with the original superselective approach. When compared with other selective multivessel strategies, the proposed technique allows for an improved and flexible adaption of the labeling focus to different anatomical variations of the arteries in the neck so that a total of five perfusion territories from the data acquired in three measurements can be recalculated in a reduced scan time. These include not only the perfusion territories of the cerebrum but also the perfusion territories in the cerebellum fed by individual vertebral arteries. Magn R... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546516 Wed, 28 Dec 2011 05:00:00 +0100 5546516 http://www.medworm.com/index.php?rid=5546515&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23091 AbstractSuperparamagnetic iron oxide nanoparticles produce changes in the surrounding microscopic magnetic field. A method for generating contrast based on the application of an adiabatic preparation pulse and the failure of the adiabatic condition surrounding the nanoparticles is introduced in this article. Images were obtained in the presence and absence of an adiabatic preparation pulse and the difference was obtained. With the use of an adiabatic full passage pulse, the contrast in the difference image depends linearly on iron concentration up to 1 mM. The use of an adiabatic zero passage pulse resulted in higher sensitivity to nanoparticles compared to the adiabatic full passage, while maintaining linear concentration dependence to 0.1 mM. This technique was shown to be insensitive to... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546515 Wed, 28 Dec 2011 05:00:00 +0100 5546515 http://www.medworm.com/index.php?rid=5546514&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23066 AbstractHyperpolarized xenon‐129 is a noninvasive contrast agent for lung MRI, which upon inhalation dissolves in parenchymal structures, thus mirroring the gas‐exchange process for oxygen in the lung. Multiple‐exchange‐time xenon polarization transfer contrast (MXTC) MRI is an implementation of the XTC MRI technique in four dimensions (three spatial dimensions plus exchange time). The aim of this study was to evaluate the sensitivity of MXTC MRI for the detection of microstructural deformations of the healthy lung in response to gravity‐induced tissue compression and the degree of lung inflation. MXTC MRI was performed in four rabbits and in three healthy human volunteers. Two lung function parameters, one related to tissue‐ to alveolar‐volume ratio and the other to average ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546514 Wed, 28 Dec 2011 05:00:00 +0100 5546514 http://www.medworm.com/index.php?rid=5546513&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24117 AbstractThe association of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2) status of breast cancer patients with total choline (tCho) concentration and tumor volume was investigated using in vivo proton magnetic resonance spectroscopy and MRI at 1.5 T. Values for tCho concentration were determined in 120 locally advanced breast cancer patients (stages IIB, IIIA, IIIB, and IIIC), 31 early breast cancer patients (stage IIA), 38 patients with benign lesions, and 37 controls. Significantly higher tCho concentration and lower tumor volume were observed in early breast cancer patients compared to locally advanced breast cancer patients (P < 0.05). tCho concentration and tumor volume did not correlate with age and menstruation. tCho cutoff values w... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546513 Wed, 28 Dec 2011 05:00:00 +0100 5546513 http://www.medworm.com/index.php?rid=5546512&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23248 AbstractStandard gradient coils are designed by minimizing the inductance or resistance for an acceptable level of gradient field nonlinearity. Recently, a new method was proposed to minimize the maximum value of the current density in a coil additionally. The stated aim of that method was to increase the minimum wire spacing and to reduce the peak temperature in a coil for fixed efficiency. These claims are tested in this study with experimental measurements of magnetic field and temperature as well as simulations of the performance of many coils. Experimental results show a 90% increase in minimum wire spacing and 40% reduction in peak temperature for equal coil efficiency and field linearity. Simulations of many more coils indicate increase in minimum wire spacing of between 50 and 340%... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546512 Wed, 28 Dec 2011 05:00:00 +0100 5546512 http://www.medworm.com/index.php?rid=5546511&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23247 AbstractFree‐breathing three‐dimensional whole‐heart coronary MRI is a noninvasive alternative to X‐ray coronary angiography. However, the existing navigator‐gated approaches do not meet the requirements of clinical practice, as they perform with suboptimal accuracy and require prolonged acquisition times. Self‐navigated techniques, applied to bright‐blood imaging sequences, promise to detect the position of the blood pool directly in the readouts acquired for imaging. Hence, the respiratory displacement of the heart can be calculated and used for motion correction with high accuracy and 100% scan efficiency. However, additional bright signal from the chest wall, spine, arms, and liver can render the isolation of the blood pool impossible. In this work, an innovative method b... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546511 Wed, 28 Dec 2011 05:00:00 +0100 5546511 http://www.medworm.com/index.php?rid=5546510&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23245 AbstractIn diffusion‐weighted imaging, multishot acquisitions are problematic due to intershot inconsistencies of the phase caused by motion during the diffusion‐encoding gradients. A model for the motion‐induced phase errors in diffusion‐weighted‐MRI of the brain is presented, in which rigid‐body and nonrigid‐body motion are separated. In the model, it is assumed that nonrigid‐body motion is due to cardiac pulsation, and that the motion patterns are repeatable from beat‐to‐beat. To test the validity of this assumption, the repeatability of nonrigid‐body motion‐induced phase errors is quantified in three healthy volunteers. Nonrigid‐body motion‐induced phase was found to significantly correlate (P < 0.05) with pulse‐oximeter waveforms in ∼83% of the pixel... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546510 Wed, 28 Dec 2011 05:00:00 +0100 5546510 http://www.medworm.com/index.php?rid=5546509&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23241 AbstractQuantitative myelin water imaging is able to show demyelinating processes and, therefore, provides insight into the pathology of white matter diseases such as multiple sclerosis. So far, mapping of the myelin water fraction most often was performed using single‐slice multiecho spin‐echo sequences. Recently, a different approach using two‐dimensional multigradient‐echo pulse sequences was suggested. In this work, a solution to three‐dimensional in vivo myelin water fraction imaging is presented that applies multigradient‐echo pulse sequences and uses non‐negative least squares algorithms to analyze the multicomponent T*2 decay. The suggested method offers not only whole brain coverage but also clinically practicable acquisition times. The obtained myelin water fraction... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546509 Wed, 28 Dec 2011 05:00:00 +0100 5546509 http://www.medworm.com/index.php?rid=5546508&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23240 AbstractTo fit high‐density receiver arrays for MRI closely around individual target anatomies, there is a need to provide a high degree of geometric adjustability with ease of handling and patient comfort. In this work, this is accomplished by the construction of a coil array that is stretchable such that it automatically conforms to a given anatomy's shape and size. Stretchability is implemented by creating the coil conductors from braided wire mounted on an elastic textile substrate. The signal‐to‐noise ratio yield of such coils is measured by MRI experiments at 3 T, and the signal‐to‐noise ratio effect of coil stretching is investigated with and without adjustment of the matching between each coil and the respective preamplifier. Four‐channel and eight‐channel arrays of s... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546508 Wed, 28 Dec 2011 05:00:00 +0100 5546508 http://www.medworm.com/index.php?rid=5546507&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23235 The objective of this work was to evaluate the dependence of pacemaker lead tip heating during MRI scanning on the electrical conductivity of the medium surrounding the pacemaker lead tip. The effect of conductivity was measured using hydroxyethyl cellulose, polyacrylic acid, and saline with conductivities ranging from 0 to 3 S/m which spans the range of human tissue conductivity. The maximum lead tip heating observed in polyacrylic acid was 50.4°C at 0.28 S/m, in hydroxyethyl cellulose the maximum was 36.8°C at 0.52 S/m, and in saline the maximum was 12.5°C at 0.51 S/m. The maximum power transfer theorem was used to calculate the relative power deposited in the solution based on the characteristic impedance of the pacemaker lead and test solution impedance. The results demonstrate a st... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546507 Wed, 28 Dec 2011 05:00:00 +0100 5546507 http://www.medworm.com/index.php?rid=5546506&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23223 AbstractEvaluation of imaging for cancer detection and localization can be achieved by correlation of gold‐standard histopathology with imaging data. Usage of a 3D biomechanical‐based deformable registration for correlation of the histopathology of whole‐tissue specimens with ex vivo imaging necessitates measurement of the distribution of biomechanical properties in the ex vivo tissue specimen and changes that occur during pathology fixation. To measure high‐resolution 3D distributions of Young's modulus (E) prefixation and postfixation, a quasi‐static magnetic resonance elastography method was developed at 7 T. Use of echo‐planar imaging allowed for shorter imaging times, in line with limited time frames allowable for pathology specimens. The finite element modeling algorithm ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546506 Wed, 28 Dec 2011 05:00:00 +0100 5546506 http://www.medworm.com/index.php?rid=5546505&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23237 AbstractChemical species separation techniques in image space are prone to incorporate several distortions. Some of these are signal accentuation in borders and geometrical warping from field inhomogeneity. These errors come from neglecting intraecho time variations. In this work, we present a new approach for chemical species separation in MRI with simultaneous estimation of field map and T decay, formulated entirely in k‐space. In this approach, the time map is used to model the phase accrual from off‐resonance precession and also the amplitude decay due to T. Our technique fits the signal model directly in k‐space with the acquired data minimizing the l2‐norm with an interior‐point algorithm. Standard two dimensional gradient echo sequences in the thighs and head were used for... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546505 Wed, 28 Dec 2011 05:00:00 +0100 5546505 http://www.medworm.com/index.php?rid=5546504&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23243 AbstractLevo‐tetrahydropalmatine (l‐THP) has shown significant promise in preclinical and clinical studies to treat drug addiction. Pharmacological MRI methods can elucidate the regional cerebral effects of l‐THP, but there are potential confounds from the use of general anesthesia. To investigate the possible anesthetic–drug interactions for the pharmacological MRI result of acute l‐THP, we examined acute blood oxygen level‐dependent responses of both 5 and 20 mg/kg l‐THP in naïve rats during general anesthesia achieved with three agents: isoflurane, medetomidine, and urethane. We found that with acute l‐THP administration, isoflurane revealed the smallest blood oxygen level‐dependent activation areas. In addition, urethane had the most activation areas; however, they w... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546504 Wed, 28 Dec 2011 05:00:00 +0100 5546504 http://www.medworm.com/index.php?rid=5546503&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23242 In this study, the effects of homodyne and projection onto convex sets reconstructions on estimates of the fractional anisotropy, mean diffusivity, and diffusion orientation in fiber tracts and raw T2‐ and trace‐weighted signal are compared, along with signal‐to‐noise ratio results. It is found that projections onto convex sets reconstruction with 3/5 segments in a 2 mm isotropic diffusion tensor image acquisition and 9/13 segments in a 0.9 × 0.9 × 4.0 mm3 diffusion‐weighted image acquisition provide good fidelity relative to the full k‐space parameters. This allows application of readout‐segmented EPI to tractography studies, and clinical stroke and oncology protocols. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc. (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546503 Wed, 28 Dec 2011 05:00:00 +0100 5546503 http://www.medworm.com/index.php?rid=5546502&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23228 AbstractWe introduce a novel method of prospectively compensating for subject motion in neuroanatomical imaging. Short three‐dimensional echo‐planar imaging volumetric navigators are embedded in a long three‐dimensional sequence, and the resulting image volumes are registered to provide an estimate of the subject's location in the scanner at a cost of less than 500 ms, ∼ 1% change in contrast, and ∼3% change in intensity. This time fits well into the existing gaps in sequences routinely used for neuroimaging, thus giving a motion‐corrected sequence with no extra time required. We also demonstrate motion‐driven selective reacquisition of k‐space to further compensate for subject motion. We perform multiple validation experiments to evaluate accuracy, navigator impact on tiss... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546502 Wed, 28 Dec 2011 05:00:00 +0100 5546502 http://www.medworm.com/index.php?rid=5546501&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23244 AbstractMR microimaging at 16.4 T with 40‐μm isotropic voxels was used to investigate compartmentation of water diffusion in formalin‐fixed prostate tissue. Ten tissue samples (∼ 28 mm3 each) from five organs were imaged. The mean diffusivity of epithelial, stromal, and ductal/acinar compartments was estimated by two methods: (1) manual region of interest selection and (2) Gaussian fitting of voxel diffusivity histograms. For the region of interest‐method, the means of the tissue sample compartment diffusivities were significantly different (P < 0.001): 0.54 ± 0.05 μm2/ms for epithelium‐containing voxels, 0.91 ± 0.17 μm2/ms for stroma, and 2.20 ± 0.04 μm2/ms for saline‐filled ducts. The means from the histogram method were also significantly different (P < 0.001): ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546501 Wed, 28 Dec 2011 05:00:00 +0100 5546501 http://www.medworm.com/index.php?rid=5546500&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24134 AbstractThe manufacturing of intravascular imaging coils poses several challenges. Due to their size, it can be difficult to incorporate local matching networks and signal amplifiers. The goal of this study is to investigate tuning and amplification strategies for intravascular coils and to assess the signal‐to‐noise benefits of incorporating a matching network and/or miniature amplifier into catheter‐based intravascular imaging devices at various locations in the signal chain. The results suggest that the use of a low‐noise amplifier close to the receiving coil enables the use of miniature coaxial cables to be used despite being noisy. Moreover, an improvement in the signal‐to‐noise ratio of over 75% is presented over conventional intravascular coil configurations where the ma... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546500 Wed, 28 Dec 2011 05:00:00 +0100 5546500 http://www.medworm.com/index.php?rid=5546499&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24131 AbstractAt high field (7 T) spectral editing of γ‐aminobutyric acid with MEGA‐point‐resolved spectroscopy is inefficient due to the large chemical shift displacement error. In this article, a new pulse sequence is designed which has minimal chemical shift displacement error to perform an efficient spectral editing of the γ‐aminobutyric acid 3.0 ppm resonance at 7 T. The sequence consists of the conventional MEGA editing pulses and a semi‐localized by adiabatic selective refocusing sequence. Phantom and in vivo measurements demonstrated an efficient detection of γ‐aminobutyric acid. Using ECG triggering, excellent in vivo performance of the MEGA‐semi‐localized by adiabatic selective refocusing (MEGA‐sLASER) provided well‐resolved γ‐aminobutyric acid signals in 27 m... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546499 Wed, 28 Dec 2011 05:00:00 +0100 5546499 http://www.medworm.com/index.php?rid=5546498&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24127 AbstractMagnetization transfer magnetic resonance imaging measurements were performed in three pancreatic ductal adenocarcinoma mouse xenograft models. For each of 28 pancreatic ductal adenocarcinoma xenografts, MT ratios (MTRs) were calculated and compared to histologic fibrosis levels from reference standard trichrome staining. MTR was found to be significantly higher in tumors grown using BxPC‐3 cell line (39.4 ± 5.1, mean ± SD) compared to the MTR for the tumors grown from Panc‐1 (32.4 ± 2.8) and Capan‐1 (27.3 ± 2.9) cell lines (P < 0.05 for each comparison). Histologic measurements showed a similar trend with BxPC‐3 tumors demonstrating significantly higher fibrosis levels (percentage of fibrotic tissue area, 6.48 ± 2.59) when compared to Panc‐1 (3.54 ± 2.18) and Ca... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546498 Wed, 28 Dec 2011 05:00:00 +0100 5546498 http://www.medworm.com/index.php?rid=5546497&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23249 This study presents quantified levels of phosphorylated metabolites in glandular tissue of human breast using 31P magnetic resonance spectroscopy at 7 T. We used a homebuilt 1H/31P radiofrequency coil to obtain artifact‐free 31P MR spectra of glandular tissue of healthy females by deploying whole breast free induction decay (FID) detection with adiabatic excitation and outer volume suppression. Using progressive saturation, the estimated apparent T1 relaxation time of 31P spins of phosphocholine and phosphoethanolamine was 4.4 and 5.7 s, respectively. Quantitative measures for phosphocholine and phosphoethanolamine levels in glandular tissue were established based on MR imaging. We used a 3D 1H image of the breast to segment the glandular tissue; this was matched to a 3D 31P image of the... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546497 Wed, 28 Dec 2011 05:00:00 +0100 5546497 http://www.medworm.com/index.php?rid=5546496&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23313 AbstractA major function of the human brain is to mediate interactions with other people. Until recently, studying social interactions as they occur within the brain was not possible due to the lack of measurable methods to observe two interacting minds simultaneously. We have developed a novel MRI dual‐head volume coil pair that can scan two subjects' brains simultaneously while the subjects are socially interacting in one MRI scanner. The feasibility of using this coil for dyadic functional MRI (fMRI) study has been successfully demonstrated for the first time. Meanwhile, an innovative robust scheme for decoupling two circular‐polarized coils (not surface coils) is introduced in theory and validated in practice in the coil technology development. Magn Reson Med, 2011. © 2011 Wiley P... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546496 Wed, 28 Dec 2011 05:00:00 +0100 5546496 http://www.medworm.com/index.php?rid=5546495&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23315 AbstractFrequently, bevacizumab is combined with chemotherapeutics such as irinotecan, motivated by studies showing improved clinical outcomes compared with historical controls. However, no systematic studies have been performed to determine if and how these drugs should be combined for optimal therapeutic response. The purpose of this study was to characterize the temporal combinations of bevacizumab and irinotecan by measuring the contrast‐agent enhanced tumor volumes and relative cerebral blood volume using dynamic susceptibility contrast imaging. The studies, performed in the U87 brain tumor model, show a vascular normalization window with bevacizumab monotherapy and are consistent with clinical indications of no additional benefit in the addition of irinotecan to bevacizumab therapy... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546495 Wed, 28 Dec 2011 05:00:00 +0100 5546495 http://www.medworm.com/index.php?rid=5546494&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23322 AbstractTissue heating during magnetic resonance measurements is a potential hazard at high‐field MRI, and particularly, in the framework of parallel radiofrequency transmission. The heating is directly related to the radiofrequency energy absorbed during an magnetic resonance examination, that is, the specific absorption rate (SAR). SAR is a pivotal parameter in MRI safety regulations, requiring reliable estimation methods. Currently used methods are usually based on models which are neither patient‐specific nor taken into account patient position and posture, which typically leads to the need for large safety margins. In this work, a novel approach is presented, which measures local SAR in a patient‐specific manner. Using a specific formulation of Maxwell's equations, the local SAR... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546494 Wed, 28 Dec 2011 05:00:00 +0100 5546494 http://www.medworm.com/index.php?rid=5546493&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24116 AbstractTo accelerate magnetic resonance imaging using uniformly undersampled (nonrandom) parallel imaging beyond what is achievable with generalized autocalibrating partially parallel acquisitions (GRAPPA) alone, the DEnoising of Sparse Images from GRAPPA using the Nullspace method is developed. The trade‐off between denoising and smoothing the GRAPPA solution is studied for different levels of acceleration. Several brain images reconstructed from uniformly undersampled k‐space data using DEnoising of Sparse Images from GRAPPA using the Nullspace method are compared against reconstructions using existing methods in terms of difference images (a qualitative measure), peak‐signal‐to‐noise ratio, and noise amplification (g‐factors) as measured using the pseudo‐multiple replica ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546493 Wed, 28 Dec 2011 05:00:00 +0100 5546493 http://www.medworm.com/index.php?rid=5546492&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24122 AbstractWith the advent of ultrahigh field systems (7T), significant improvements in spectroscopic imaging (SI) studies of the human brain have been anticipated. These gains are dependent upon the achievable B0 homogeneity, both globally (σB, over the entire regions of interest or slice) and locally (σB, influencing the linewidth of individual SI voxels within the regions of interest). Typically the B0 homogeneity is adjusted using shim coils with spatial distributions modeled on spherical harmonics which can be characterized by a degree (radial dependence) and order (azimuthal symmetry). However, the role of very high order and degree shimming (e.g., 3rd and 4th degree) in MRSI studies has been controversial. Measurements of σB and σB were determined from B0 field maps of 64 × 64 res... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546492 Wed, 28 Dec 2011 05:00:00 +0100 5546492 http://www.medworm.com/index.php?rid=5546491&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24123 This study explored the feasibility, sensitivity, and specificity of in vivo chromium‐enhanced MRI of retinal lipids by determining its spatiotemporal profiles and toxic effect after intravitreal Cr(VI) injection to normal adult rats. One day after 3 μL Cr(VI) administration at 1–100 mM, the retina exhibited a dose‐dependent increase in T1‐weighted hyperintensity until 50 mM. Time‐dependently, significant T1‐weighted hyperintensity persisted up to 2 weeks after 10 mM Cr(VI) administration. Three‐dimensional chromium‐enhanced MRI of ex vivo normal eyes at isotropic 50‐μm resolution showed at least five alternating bands across retinal layers, with the outermost layer being the brightest. This agreed with histology indicating alternating lipid contents with the highest le... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546491 Wed, 28 Dec 2011 05:00:00 +0100 5546491 http://www.medworm.com/index.php?rid=5546490&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24124 AbstractMultishot spiral imaging is a promising alternative to echo‐planar imaging for high‐resolution diffusion‐weighted imaging and diffusion tensor imaging. However, subject motion in the presence of diffusion‐weighting gradients causes phase inconsistencies among different shots, resulting in signal loss and aliasing artifacts in the reconstructed images. Such artifacts can be reduced using a variable‐density spiral trajectory or a navigator echo, however at the cost of a longer scan time. Here, a novel iterative phase correction method is proposed to inherently correct for the motion‐induced phase errors without requiring any additional scan time. In this initial study, numerical simulations and in vivo experiments are performed to demonstrate that the proposed method can ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546490 Wed, 28 Dec 2011 05:00:00 +0100 5546490 http://www.medworm.com/index.php?rid=5546526&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23317 This article reports a novel method for correcting the distortions observed in EPI acquired at ultra‐high‐field such as 7 T. Point spread function (PSF) mapping methods have been proposed for correcting the distortions in EPI. The PSF shift map can be derived either along the nondistorted or the distorted coordinates. Along the nondistorted coordinates more information about compressed areas is present but it is prone to PSF‐ghosting artifacts induced by large k‐space shift in PSF encoding direction. In contrast, shift maps along the distorted coordinates contain more information in stretched areas and are more robust against PSF‐ghosting. In ultra‐high‐field MRI, an EPI contains both compressed and stretched regions depending on the B0 field inhomogeneity and local susceptib... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546526 Tue, 27 Dec 2011 05:00:00 +0100 5546526 http://www.medworm.com/index.php?rid=5546525&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23308 AbstractDiffusion tensor imaging is widely used in research and clinical applications, but still suffers from substantial artifacts. Here, we focus on vibrations induced by strong diffusion gradients in diffusion tensor imaging, causing an echo shift in k‐space and consequential signal‐loss. We refined the model of vibration‐induced echo shifts, showing that asymmetric k‐space coverage in widely used Partial Fourier acquisitions results in locally differing signal loss in images acquired with reversed phase encoding direction (blip‐up/blip‐down). We implemented a correction of vibration artifacts in diffusion tensor imaging using phase‐encoding reversal (COVIPER) by combining blip‐up and blip‐down images, each weighted by a function of its local tensor‐fit error. COVIPE... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546525 Tue, 27 Dec 2011 05:00:00 +0100 5546525 http://www.medworm.com/index.php?rid=5546524&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23302 AbstractThe exchange of water molecules between the inner sphere of a paramagnetic chemical exchange saturation transfer (PARACEST) contrast agent and bulk water can shorten the bulk water T2 through the T2‐exchange (T2ex) mechanism. The line‐broadening T2ex effect is proportional to the agent concentration, the chemical shift of the exchanging water molecule, and is highly dependent on the water molecule exchange rate. A significant T2ex contribution to the bulk water linewidth can make the regions of agent uptake appear dark when imaging with conventional sequences like gradient‐echo and fast spin‐echo. The minimum echo times for these sequences (1–10 ms) are not fast enough to capture signal from the regions of shortened T2. This makes “Off” (saturation at −Δω) minus �... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546524 Tue, 27 Dec 2011 05:00:00 +0100 5546524 http://www.medworm.com/index.php?rid=5546523&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23268 AbstractThe in vivo pain treatment was successfully performed with the patient in a prone position. The PD‐weighted TSE with echo time = 10 ms rendered contrast‐to‐noise‐ratio values of 27 ± 10 for needle/fat, 1.6 ± 5 for needle/muscle, and 4 ± 4.7 for needle/nerve tissue. The mean diameter of the needle artifact was 1.2 ± 0.2 mm. In the T1‐weighted gradient echo, the needle's artifact diameter was 6 ± 2 mm; the needle's contrast‐to‐noise ratio relative to muscle tissue was 4 ± 2, 7.6 ± 1.5 for needle/fat, and 5 ± 1 for needle/nerve tissue. With the PD‐weighted TSE (echo time = 10 ms) and the T1‐weighted gradient echo, the needle was imaged reliably throughout the intervention. The butterfly surface coil is feasible for the guidance of spinal interventions in a pr... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546523 Tue, 27 Dec 2011 05:00:00 +0100 5546523 http://www.medworm.com/index.php?rid=5546522&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23264 In this study, we investigate the potential of using adiabatic TSE at 7 T with surface coil transceivers in human applications. The adiabatic RF pulses were tuned to deal with the constraints in B1 strength and RF power deposition, but remained in the superadiabatic regime. As a consequence, the dynamic range in B1 is compromised, and signal modulation is obtained over the echo train. Multidimensional Bloch simulations over the echo train and phantom measurements were obtained to assess these limitations. Still, using proper k‐space sampling, we demonstrate improved image quality of the adiabatic TSE versus conventional TSE in the brain, the neck (carotid artery) and in the pelvis (prostate) at 7 T. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc. (Source: Magnetic Resonance in Medi... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546522 Tue, 27 Dec 2011 05:00:00 +0100 5546522 http://www.medworm.com/index.php?rid=5546521&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23250 AbstractThe sensitivity of chemical exchange saturation transfer (CEST) on glycosaminoglycans (GAGs) in human knee cartilage (gagCEST) in vivo was evaluated at 3 and 7 T field strengths. Calculated gagCEST values without accounting for B0 inhomogeneity (∼0.6 ppm) were >20%. After B0 inhomogeneity correction, calculated gagCEST values were negligible at 3 T and ∼6% at 7 T. These results suggest that accurate B0 correction is a prerequisite for observing reliable gagCEST. Results obtained with varying saturation pulse durations and amplitudes as well as the consistency between numerical simulations and our experimental results indicate that the negligible gagCEST observed at 3 T is due to direct saturation effects and fast exchange rate. As GAG loss from cartilage is expected to resul... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546521 Tue, 27 Dec 2011 05:00:00 +0100 5546521 http://www.medworm.com/index.php?rid=5546520&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23319 AbstractParallel transmission has been used to reduce the inevitable inhomogeneous radiofrequency fields produced in human high‐field MRI greater than 3 T. Further improvements in the transmit homogeneity and efficiency are possible by leveraging the additional degree of freedom permitted by multislice acquisitions. Compared to simple scaling of the flip angle to compensate for B1+ falloff along the radiofrequency coil, calculation of B1+ shim solutions on a slice‐by‐slice basis can markedly improve homogeneity and/or reduce transmitted power and global SAR. Performance measures were acquired at 7 T with a 15‐channel head‐only transceive array featuring elements distributed over all three logical axes, facilitating B1+ shimming over arbitrary orientations. Compared to a circularl... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5546520 Tue, 27 Dec 2011 05:00:00 +0100 5546520 http://www.medworm.com/index.php?rid=5542776&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22190168%26dopt%3DAbstract Authors: Beyers RJ, Smith RS, Xu Y, Piras BA, Salerno M, Berr SS, Meyer CH, Kramer CM, French BA, Epstein FH Abstract In matched slices of a mouse heart acquired 2 days after a 20-min coronary artery occlusion, the area of infarction as assessed by hyperintensity on late gadolinium-enhanced (LGE) T(1) -weighted CMR (a) is a subregion of the area at risk (AAR) as assessed by hyperintensity on T(2) -weighted CMR (b). Histology of the same slice is shown in (c), where nonblue indicates AAR, white indicates necrotic infarction, red/pink indicates the salvaged area from the article by Beyers et al (pp 201-209). PMID: 22190168 [PubMed - in process] (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542776 Mon, 26 Dec 2011 20:25:22 +0100 5542776 http://www.medworm.com/index.php?rid=5528331&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24159 (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5528331 Thu, 22 Dec 2011 21:07:45 +0100 5528331 http://www.medworm.com/index.php?rid=5528330&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.24160 AbstractIn matched slices of a mouse heart acquired 2 days after a 20‐min coronary artery occlusion, the area of infarction as assessed by hyperintensity on late gadolinium‐enhanced (LGE) T1‐weighted CMR (a) is a subregion of the area at risk (AAR) as assessed by hyperintensity on T2‐weighted CMR (b). Histology of the same slice is shown in (c), where nonblue indicates AAR, white indicates necrotic infarction, red/pink indicates the salvaged area from the article by Beyers et al (pp 201–209). (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5528330 Thu, 22 Dec 2011 21:07:44 +0100 5528330 http://www.medworm.com/index.php?rid=5528314&cid=s_36811_37_f&fid=33601&url=http%3A%2F%2Fdx.doi.org%2F10.1002%252Fmrm.23232 This study investigated a modified encoding strategy for CPMG BS‐based methods to overcome this limitation. By applying a “bipolar” off‐resonant BS pulse before the refocusing pulse train, the needed phase information was able to be encoded into different echo images of one echo train. Thus, this technique allowed simultaneous B and T2 mapping in a single BS‐CPMG‐MSE experiment. To allow single‐shot B mapping, this method was also applied to turbo‐spin echo imaging. Furthermore, the presented modification intrinsically minimizes phase‐based image artifacts in BS‐CPMG‐TSE experiments. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc. (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5528314 Thu, 22 Dec 2011 21:02:41 +0100 5528314 http://www.medworm.com/index.php?rid=5542783&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22189760%26dopt%3DAbstract Authors: Berglund J, Kullberg J Abstract The chemical shift of water and fat resonances in proton MRI allows separation of water and fat signal from chemical shift encoded data. This work describes an automatic method that produces separate water and fat images as well as quantitative maps of fat signal fraction and T 2* from complex multiecho gradient-recalled datasets. Accurate water and fat separation is challenging due to signal ambiguity at the voxel level. Whole-image optimization can resolve this ambiguity, but might be computationally demanding, especially for three-dimensional data. In this work, periodicity of the model fit residual as a function of the off-resonance was used to modify a previously proposed formulation of the problem. This gives a smaller solution space... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542783 Wed, 21 Dec 2011 05:00:00 +0100 5542783 http://www.medworm.com/index.php?rid=5542782&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22189839%26dopt%3DAbstract Authors: Gonçalves SI, Ziech ML, Lamerichs R, Stoker J, Nederveen AJ Abstract Magnetic resonance imaging is widely used in the work-up and monitoring of patients with Crohn's disease. Balanced steady-state free precession sequences are an important part of the imaging protocol and until now primarily 1.5T scanners have been used in daily clinical practice. This is largely because running balanced steady-state free precession sequences in 3T magnets has technical problems related to increased B(0) inhomogeneity and specific absorption rate (SAR) deposition. A modified form of alternating repetition time steady-state free precession sequence is presented to acquire 3D-isotropic abdominal images with fat-suppression at 3T within a breath-hold. The modifications include an adjusted ra... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542782 Wed, 21 Dec 2011 05:00:00 +0100 5542782 http://www.medworm.com/index.php?rid=5542781&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22189904%26dopt%3DAbstract Authors: Addy NO, Wu HH, Nishimura DG Abstract Fast imaging trajectories are used in MRI to speed up the acquisition process, but imperfections in the gradient system create artifacts in the reconstructed images. Artifacts result from the deviation between k-space trajectories achieved on the scanner and their original prescription. Measuring or approximating actual k-space trajectories with predetermined gradient timing delays reduces the artifacts, but are generally based on a specific trajectory and scan orientation. A single linear time-invariant characterization of the gradient system provides a method to predict k-space trajectories scanned in arbitrary orientations through convolution. This is done efficiently, by comparing the Fourier transforms of the input and measured wa... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542781 Wed, 21 Dec 2011 05:00:00 +0100 5542781 http://www.medworm.com/index.php?rid=5542780&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22189961%26dopt%3DAbstract Authors: Lee W, Janik R, Scouten A, Stefanovic B, Sled JG Abstract Arterial spin labeling can be used to measure both cerebral perfusion and arterial transit time. However, accurate estimation of these parameters requires adequate temporal sampling of the arterial spin labeling difference signal. In whole-brain multislice acquisitions, two factors reduce the accuracy of the parameter estimates: saturation of labeled blood in transit and inadequate sampling of early difference signal in superior slices. Label saturation arises when slices are acquired inferior-to-superior such that slice selection in proximal slices spoils the label for a distal slice. Inadequate sampling arises when the time spent acquiring inferior slices is too long to allow early sampling of the difference signa... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542780 Wed, 21 Dec 2011 05:00:00 +0100 5542780 http://www.medworm.com/index.php?rid=5542779&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22190042%26dopt%3DAbstract Authors: Yarnykh VL Abstract A new method was developed for fast quantitative mapping of the macromolecular proton fraction defined within the two-pool model of magnetization transfer. The method utilizes a single image with off-resonance saturation, a reference image for data normalization, and T(1) , B(0) , and B(1) maps with the total acquisition time ∼10 min for whole-brain imaging. Macromolecular proton fraction maps are reconstructed by iterative solution of the matrix pulsed magnetization transfer equation with constrained values of other model parameters. Theoretical error model describing the variance due to noise and the bias due to deviations of constrained parameters from their actual values was formulated based on error propagation rules. The method was validated by ... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542779 Wed, 21 Dec 2011 05:00:00 +0100 5542779 http://www.medworm.com/index.php?rid=5542778&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22190079%26dopt%3DAbstract Authors: Mishkovsky M, Cheng T, Comment A, Gruetter R Abstract In vivo localized and fully adiabatic homonuclear and heteronuclear polarization transfer experiments were designed and performed in the rat brain at 9.4 T after infusion of hyperpolarized sodium [1,2-(13) C(2) ] and sodium [1-(13) C] acetate. The method presented herein leads to highly enhanced in vivo detection of short-T(1) (13) C as well as attached protons. This indirect detection scheme allows for probing additional molecular sites in hyperpolarized substrates and their metabolites and can thus lead to improved spectral resolution such as in the case of (13) C-acetate metabolism. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc. PMID: 22190079 [PubMed - as supplied by publisher] (Source: Magnetic Res... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542778 Wed, 21 Dec 2011 05:00:00 +0100 5542778 http://www.medworm.com/index.php?rid=5542777&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22190144%26dopt%3DAbstract This study investigated a modified encoding strategy for CPMG BS-based methods to overcome this limitation. By applying a "bipolar" off-resonant BS pulse before the refocusing pulse train, the needed phase information was able to be encoded into different echo images of one echo train. Thus, this technique allowed simultaneous B 1+ and T(2) mapping in a single BS-CPMG-MSE experiment. To allow single-shot B 1+ mapping, this method was also applied to turbo-spin echo imaging. Furthermore, the presented modification intrinsically minimizes phase-based image artifacts in BS-CPMG-TSE experiments. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc. PMID: 22190144 [PubMed - as supplied by publisher] (Source: Magnetic Resonance in Medicine) Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542777 Wed, 21 Dec 2011 05:00:00 +0100 5542777 http://www.medworm.com/index.php?rid=5542775&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22190173%26dopt%3DAbstract Authors: Mao XA Abstract In application of the (31) P selectively refocused insensitive nuclei enhanced polarization transfer (srINEPT) technique to the detection of phosphomono- and diesters in tissues, homonuclear couplings between the CH(2) O protons and the NCH(2) protons seriously attenuate the sensitivity. These couplings can be conventionally removed by two soft 180° pulses in the (1) H evolution period which selectively invert the NCH(2) magnetizations. However, the srINEPT pulse sequence can be simplified by replacing the pulse train "soft 180°-hard 180°-soft 180°" with a single soft 180° pulse that selectively inverts the CH(2) O magnetizations. Theoretical analysis in this study demonstrates the correctness of this approach in principle. Validation on a milk phantom... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542775 Wed, 21 Dec 2011 05:00:00 +0100 5542775 http://www.medworm.com/index.php?rid=5542774&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22190225%26dopt%3DAbstract Authors: Chung J, Dash R, Kee K, Barral JK, Kosuge H, Robbins RC, Nishimura D, Reijo-Pera RA, Yang PC Abstract Although human embryonic stem cell (hESC) hold therapeutic potential, teratoma formation has deterred clinical translation. Manganese (Mn(2+) ) enters metabolically active cells through voltage-gated calcium channels and subsequently, induces T(1) shortening. We hypothesized that serial manganese-enhanced MRI would have theranostic effect to assess hESC survival, teratoma formation, and hESC-derived teratoma reduction through intracellular accumulation of Mn(2+) . Firefly luciferase transduced hESCs (hESC-Lucs) were transplanted into severe combined immunodeficient mouse hindlimbs to form teratoma. The chemotherapy group was injected with MnCl(2) intraperitoneally three ti... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542774 Wed, 21 Dec 2011 05:00:00 +0100 5542774 http://www.medworm.com/index.php?rid=5542773&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22190255%26dopt%3DAbstract This article presents a general method for reconstruction of high spatial and temporal resolution cine images from a real-time acquisition acquired over multiple cardiac cycles. The method combines parallel imaging and motion correction based on nonrigid registration and can be applied to arbitrary k-space trajectories. The method is demonstrated with real-time Cartesian imaging and Golden Angle radial acquisitions, and the motion-corrected acquisitions are compared with raw real-time images and breath-hold cine acquisitions in 10 (N = 10) subjects. Acceptable image quality was obtained in all motion-corrected reconstructions, and the resulting mean image quality score was (a) Cartesian real-time: 2.48, (b) Golden Angle real-time: 1.90 (1.00-2.50), (c) Cartesian motion correction: 3.92, (d... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542773 Wed, 21 Dec 2011 05:00:00 +0100 5542773 http://www.medworm.com/index.php?rid=5542772&cid=s_36811_37_f&fid=36811&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22190282%26dopt%3DAbstract Authors: Johnson CB, Tikunov AP, Lee H, Wolak JE, Pediaditakis P, Romney DA, Holmuhamedov E, Gamcsik MP, Macdonald JM Abstract The glycine cleavage system (GCS), the major pathway of glycine catabolism in liver, is found only in the mitochondria matrix and is regulated by the oxidized nicotinamide adenine dinucleotide (NAD(+) )/reduced nicotinamide adenine dinucleotide (NADH) ratio. In conjunction with serine hydroxymethyltransferase, glycine forms the 1 and 2 positions of serine, while the 3 position is formed exclusively by GCS. Therefore, we sought to exploit this pathway to show that quantitative measurements of serine isotopomers in liver can be used to monitor the NAD(+) /NADH ratio using (13) C NMR spectroscopy. Rat hepatocytes were treated with modulators of GCS activity fo... Magnetic Resonance in Medicine journals http://www.medworm.com/rss/comments.php?id=5542772 Wed, 21 Dec 2011 05:00:00 +0100 5542772