Magnetic Resonance in MedicineThis is an RSS file. You can use it to subscribe to this data in your favourite RSS reader, such as GoogleReader, or to display this data on your own website or blog. Subscribe to this data using MyMedWorm.Subscribe to this data using GoogleReader.Subscribe to this data using Bloglines.Subscribe to this data using MyYahoo.

Get the very latest Swine Flu news via the MedWorm Swine Flu RSS news feed - updated hourly from thousands of authoritative health and news sources.

• Contents
• Discussions

Pages: 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  

The impact of the relaxivity definition on the quantitative measurement of glycosaminoglycans in cartilage by the MRI dGEMRIC methodEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The relaxivities (R-values) of the gadolinium diethylene triamine pentaacetic acid (Gd(DTPA)2-) ions in a series of skim-milk solutions at 0-40% milk concentrations were measured using NMR spectroscopy. The R-value was found to be approximately linearly proportional to the concentration of the solid component in the milk solution. Using the R-value at 20% solid component (approximately the solid concentration in bovine nasal cartilage), the glycosaminoglycan concentration in bovine nasal cartilage can be quantified using the MRI delayed gadolinium-enhanced MRI of cartilage method without the customary scaling factor of 2. ...
Source: Magnetic Resonance in Medicine - November 14, 2009 Category: Radiology Authors: ShaoKuan Zheng, Yang Xia Source Type: journals

An MR-compatible bicycle ergometer for in-magnet whole-body human exercise testing.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An MR-compatible ergometer was developed for in-magnet whole-body human exercise testing. Designed on the basis of conventional mechanically braked bicycle ergometers and constructed from nonferrous materials, the ergometer was implemented on a 1.5-T whole-body MR scanner. A spectrometer interface was constructed using standard scanner hardware, complemented with custom-built parts and software to enable gated data acquisition during exercise. High-quality (31)P NMR spectra were reproducibly obtained from the medial head of the quadriceps muscle of the right leg of eight healthy subjects during two-legged high-frequenc...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Jeneson JA, Schmitz JP, Hilbers PA, Nicolay K Tags: Magn Reson Med Source Type: journals

Change in the proton T(1) of fat and water in mixture.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This work describes observed changes in the proton T(1) relaxation time of both water and lipid when they are in relatively homogeneous mixtures. Results obtained from vegetable oil-water emulsions, pork kidney and lard mixtures, and excised samples of white and brown adipose tissues are presented to demonstrate this change in T(1) as a function of mixture fat fraction. As an initial proof of concept, a simpler acetone-water experiment was performed to take advantage of complete miscibility between acetone and water and both components' single chemical shift peaks. Single-voxel MR spectroscopy was used to measure the T...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Hu HH, Nayak KS Tags: Magn Reson Med Source Type: journals

A multislice gradient echo pulse sequence for CEST imaging.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Chemical exchange-dependent saturation transfer and paramagnetic chemical exchange-dependent saturation transfer are agent-mediated contrast mechanisms that depend on saturating spins at the resonant frequency of the exchangeable protons on the agent, thereby indirectly saturating the bulk water. In general, longer saturating pulses produce stronger chemical and paramagnetic exchange-dependent saturation transfer effects, with returns diminishing for pulses longer than T(1). This could make imaging slow, so one approach to chemical exchange-dependent saturation transfer imaging has been to follow a long, frequency-sele...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Dixon WT, Hancu I, Ratnakar SJ, Sherry AD, Lenkinski RE, Alsop DC Tags: Magn Reson Med Source Type: journals

A short-breath-hold technique for lung pO(2) mapping with (3)He MRI.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A pulse-sequence strategy was developed for generating regional maps of alveolar oxygen partial pressure (pO(2)) in a single 6-sec breath hold, for use in human subjects with impaired lung function. Like previously described methods, pO(2) values are obtained by measuring the oxygen-induced T(1) relaxation of inhaled hyperpolarized (3)He. Unlike other methods, only two (3)He images are acquired: one with reverse-centric and the other with centric phase-encoding order. This phase-encoding arrangement minimizes the effects of regional flip-angle variations, so that an accurate map of instantaneous pO(2) can be calculated...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Miller GW, Mugler JP, Altes TA, Cai J, Mata JF, de Lange EE, Tobias WA, Cates GD, Brookeman JR Tags: Magn Reson Med Source Type: journals

Navigator accuracy requirements for prospective motion correction.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Prospective motion correction in MRI is becoming increasingly popular to prevent the image artifacts that result from subject motion. Navigator information is used to update the position of the imaging volume before every spin excitation so that lines of acquired k-space data are consistent. Errors in the navigator information, however, result in residual errors in each k-space line. This paper presents an analysis linking noise in the tracking system to the power of the resulting image artifacts. An expression is formulated for the required navigator accuracy based on the properties of the imaged object and the desire...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Maclaren J, Speck O, Stucht D, Schulze P, Hennig J, Zaitsev M Tags: Magn Reson Med Source Type: journals

Phase-unwrapping algorithm for translation extraction from spherical navigator echoes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Spherical navigator echoes have been shown to determine rigid-body rotation and translation simultaneously. Following the determination of rotation, translations are determined from the phase change between the baseline and transformed spherical navigator echoes. Because the measured phase change is limited in the interval (-pi, pi), a phase-unwrapping algorithm is required to recover the true phase change in absolute values. The unwrapping algorithm presented in this article is based on a priori information about the true translation-induced phase-change function. The algorithm is verified using simulation and in vivo...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Liu J, Drangova M Tags: Magn Reson Med Source Type: journals

An expandable catheter loop coil for intravascular MRI in larger blood vessels.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The present study proposes a catheter system with an expandable coil etched on a polyimide foil. The catheter system combines the advantages of a small insertion diameter when the coil is rolled up in a protective carrier sheath with an increased signal-to-noise ratio (SNR) and penetration depth when the coil is pushed out. After imaging, the coil can be retracted into the sheath and folded back into the initial rolled-up configuration due to the tapered geometry of the carrier foil. The catheter system was tested on two healthy anesthetized pigs, including tracking and high-resolution intravascular imaging. To reduce ...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Homagk AK, Umathum R, Korn M, Weber MA, Hallscheidt P, Semmler W, Bock M Tags: Magn Reson Med Source Type: journals

MRI using radiofrequency magnetic field phase gradients.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Conventionally, MR images are formed by applying gradients to the main static magnetic field (B(0)). However, the B(0) gradient equipment is expensive, power-hungry, complex, and noisy and can induce eddy currents in nearby conducting structures, including the patient. Here, we describe a new silent, B(0) gradient-free MRI principle, Transmit Array Spatial Encoding (TRASE), based on phase gradients of the radio-frequency (RF) field. RF phase gradients offer a new method of k-space traversal. Echo trains using at least two different RF phase gradients allow spin phase to accumulate, causing k-space traversal. Two such R...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Sharp JC, King SB Tags: Magn Reson Med Source Type: journals

The impact of the relaxivity definition on the quantitative measurement of glycosaminoglycans in cartilage by the MRI dGEMRIC method.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The relaxivities (R-values) of the gadolinium diethylene triamine pentaacetic acid (Gd(DTPA)(2-)) ions in a series of skim-milk solutions at 0-40% milk concentrations were measured using NMR spectroscopy. The R-value was found to be approximately linearly proportional to the concentration of the solid component in the milk solution. Using the R-value at 20% solid component (approximately the solid concentration in bovine nasal cartilage), the glycosaminoglycan concentration in bovine nasal cartilage can be quantified using the MRI delayed gadolinium-enhanced MRI of cartilage method without the customary scaling factor ...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Zheng S, Xia Y Tags: Magn Reson Med Source Type: journals

Quantification of T(2) in the abdomen at 3.0 T using a T(2)-prepared balanced turbo field echo sequence.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The T(2)-prepared balanced turbo field echo sequence has been used to measure T(2) in phantoms and in vivo in the abdomen with low sensitivity to radiofrequency pulse errors. The effects of noise, errors in the pulse flip angles, and off resonance effects on the results have been simulated. It was found from simulations that for normal conditions, including the flip angle in the fit improved the systematic errors due to radiofrequency pulse errors and noise in the results to less than 1% without significantly increasing the random errors. For a 0.3% noise level, the standard deviation in the measured T(2) was approxima...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Hoad CL, Cox EF, Gowland PA Tags: Magn Reson Med Source Type: journals

T(2) relaxation time abnormalities in bipolar disorder and schizophrenia.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
There are substantial abnormalities in the number, density, and size of cortical neurons and glial cells in bipolar disorder and schizophrenia. Because molecule-microenvironment interactions modulate metabolite signals characteristics, these cellular abnormalities may impact transverse (T(2)) relaxation times. We measured T(2) relaxation times for three intracellular metabolites (N-acetylaspartate + N-acetylaspartylglutamate, creatine + phosphocreatine, and choline-containing compounds) in the anterior cingulate cortex and parieto-occipital cortex from 20 healthy subjects, 15 patients with bipolar disorder, and 15 pati...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Ongür D, Prescot AP, Jensen JE, Rouse ED, Cohen BM, Renshaw PF, Olson DP Tags: Magn Reson Med Source Type: journals

RF shimming for spectroscopic localization in the human brain at 7 T.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Spectroscopic imaging of the human head at short echo times (</=15 ms) typically requires suppression of signals from extracerebral tissues. However, at 7 T, decreasing efficiency in B(1) (+) generation (hertz/watt) and increasing spectral bandwidth result in dramatic increases in power deposition and increased chemical shift registration artifacts for conventional gradient-based in-plane localization. In this work, we describe a novel method using radiofrequency shimming and an eight-element transceiver array to generate a B(1) (+) field distribution that excites a ring about the periphery of the head and leaves ce...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Hetherington HP, Avdievich NI, Kuznetsov AM, Pan JW Tags: Magn Reson Med Source Type: journals

Longitudinal analysis of MRI T(2) knee cartilage laminar organization in a subset of patients from the osteoarthritis initiative.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The purpose of this pilot study was to longitudinally quantify the T(2) laminar integrity of knee cartilage in a subset of subjects with osteoarthritis from the Osteoarthritis Initiative at baseline, 1-year follow-up, and 2-year follow-up. Cartilage from 13 subjects was divided into six compartments and subdivided into deep and superficial layers. At each time point, mean T(2) values in superficial and deep layers were compared. Longitudinal analysis included full-thickness mean T(2), mean deep T(2), mean superficial T(2), mean T(2) laminar difference, mean percentage T(2) laminar difference, and two-dimensional measur...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Carballido-Gamio J, Blumenkrantz G, Lynch JA, Link TM, Majumdar S Tags: Magn Reson Med Source Type: journals

Improved signal to noise in proton spectroscopy of the human calf muscle at 7 T using localized B(1) calibration.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Large variations of tip angle within a slice can lead to suboptimal pulse power optimization using standard techniques, which measure the average tip angle over a slice; this effect is especially pronounced at fields of 7 T and above. A technique was introduced that performed a volume-selective power optimization in less than 10 sec and automatically calibrates the radiofrequency pulses for subsequent spectroscopy scans. Using this technique, MR spectra were acquired in the human calf of seven healthy volunteers with a partial volume Tx/Rx coil. Increases in signal-to-noise ratio based upon the unsuppressed water signa...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Versluis MJ, Kan HE, van Buchem MA, Webb AG Tags: Magn Reson Med Source Type: journals

Motion correction using an enhanced floating navigator and GRAPPA operations.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A method for motion correction in multicoil imaging applications, involving both data collection and reconstruction, is presented. The floating navigator method, which acquires a readout line off center in the phase-encoding direction, is expanded to detect translation/rotation and inconsistent motion. This is done by comparing floating navigator data with a reference k-space region surrounding the floating navigator line, using a correlation measure. The technique of generalized autocalibrating partially parallel acquisition is further developed to correct for a fully sampled, motion-corrupted dataset. The flexibility...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Lin W, Huang F, Börnert P, Li Y, Reykowski A Tags: Magn Reson Med Source Type: journals

Magnetic field homogenization of the human prefrontal cortex with a set of localized electrical coils.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The prefrontal cortex is a common target brain structure in psychiatry and neuroscience due to its role in working memory and cognitive control. Large differences in magnetic susceptibility between the air-filled sinuses and the tissue/bone in the frontal part of the human head cause a strong and highly localized magnetic field focus in the prefrontal cortex. As a result, image distortion and signal dropout are observed in MR imaging. A set of external electrical coils is presented that provides localized and high-amplitude shim fields in the prefrontal cortex, with minimum impact on the rest of the brain when combined...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Juchem C, Nixon TW, McIntyre S, Rothman DL, de Graaf RA Tags: Magn Reson Med Source Type: journals

Quantification of T2 in the abdomen at 3.0 T using a T2-prepared balanced turbo field echo sequenceEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The T2-prepared balanced turbo field echo sequence has been used to measure T2 in phantoms and in vivo in the abdomen with low sensitivity to radiofrequency pulse errors. The effects of noise, errors in the pulse flip angles, and off resonance effects on the results have been simulated. It was found from simulations that for normal conditions, including the flip angle in the fit improved the systematic errors due to radiofrequency pulse errors and noise in the results to less than 1% without significantly increasing the random errors. For a 0.3% noise level, the standard deviation in the measured T2 was approximately 0.003...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Caroline L. Hoad, Eleanor F. Cox, Penny A. Gowland Source Type: journals

An MR-compatible bicycle ergometer for in-magnet whole-body human exercise testingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An MR-compatible ergometer was developed for in-magnet whole-body human exercise testing. Designed on the basis of conventional mechanically braked bicycle ergometers and constructed from nonferrous materials, the ergometer was implemented on a 1.5-T whole-body MR scanner. A spectrometer interface was constructed using standard scanner hardware, complemented with custom-built parts and software to enable gated data acquisition during exercise. High-quality 31P NMR spectra were reproducibly obtained from the medial head of the quadriceps muscle of the right leg of eight healthy subjects during two-legged high-frequency peda...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Jeroen A. L. Jeneson, Joep P. J. Schmitz, Peter A. J. Hilbers, Klaas Nicolay Source Type: journals

A short-breath-hold technique for lung pO2 mapping with 3He MRIEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A pulse-sequence strategy was developed for generating regional maps of alveolar oxygen partial pressure (pO2) in a single 6-sec breath hold, for use in human subjects with impaired lung function. Like previously described methods, pO2 values are obtained by measuring the oxygen-induced T1 relaxation of inhaled hyperpolarized 3He. Unlike other methods, only two 3He images are acquired: one with reverse-centric and the other with centric phase-encoding order. This phase-encoding arrangement minimizes the effects of regional flip-angle variations, so that an accurate map of instantaneous pO2 can be calculated from two images...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: G. Wilson Miller, John P. Mugler III, Talissa A. Altes, Jing Cai, Jaime F. Mata, Eduard E. de Lange, William A. Tobias, Gordon D. Cates, James R. Brookeman Source Type: journals

RF shimming for spectroscopic localization in the human brain at 7 TEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Spectroscopic imaging of the human head at short echo times ([le]15 ms) typically requires suppression of signals from extracerebral tissues. However, at 7 T, decreasing efficiency in B1+ generation (hertz/watt) and increasing spectral bandwidth result in dramatic increases in power deposition and increased chemical shift registration artifacts for conventional gradient-based in-plane localization. In this work, we describe a novel method using radiofrequency shimming and an eight-element transceiver array to generate a B1+ field distribution that excites a ring about the periphery of the head and leaves central brain regi...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Hoby P. Hetherington, Nikolai I. Avdievich, Andrey M. Kuznetsov, Jullie W. Pan Source Type: journals

MRI using radiofrequency magnetic field phase gradientsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Conventionally, MR images are formed by applying gradients to the main static magnetic field (B0). However, the B0 gradient equipment is expensive, power-hungry, complex, and noisy and can induce eddy currents in nearby conducting structures, including the patient. Here, we describe a new silent, B0 gradient-free MRI principle, Transmit Array Spatial Encoding (TRASE), based on phase gradients of the radio-frequency (RF) field. RF phase gradients offer a new method of k-space traversal. Echo trains using at least two different RF phase gradients allow spin phase to accumulate, causing k-space traversal. Two such RF fields p...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Jonathan C. Sharp, Scott B. King Source Type: journals

Navigator accuracy requirements for prospective motion correctionEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Prospective motion correction in MRI is becoming increasingly popular to prevent the image artifacts that result from subject motion. Navigator information is used to update the position of the imaging volume before every spin excitation so that lines of acquired k-space data are consistent. Errors in the navigator information, however, result in residual errors in each k-space line. This paper presents an analysis linking noise in the tracking system to the power of the resulting image artifacts. An expression is formulated for the required navigator accuracy based on the properties of the imaged object and the desired re...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Julian Maclaren, Oliver Speck, Daniel Stucht, Peter Schulze, Jürgen Hennig, Maxim Zaitsev Source Type: journals

A multislice gradient echo pulse sequence for CEST imagingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Chemical exchange-dependent saturation transfer and paramagnetic chemical exchange-dependent saturation transfer are agent-mediated contrast mechanisms that depend on saturating spins at the resonant frequency of the exchangeable protons on the agent, thereby indirectly saturating the bulk water. In general, longer saturating pulses produce stronger chemical and paramagnetic exchange-dependent saturation transfer effects, with returns diminishing for pulses longer than T1. This could make imaging slow, so one approach to chemical exchange-dependent saturation transfer imaging has been to follow a long, frequency-selective ...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: W. Thomas Dixon, Ileana Hancu, S. James Ratnakar, A. Dean Sherry, Robert E. Lenkinski, David C. Alsop Source Type: journals

Improved signal to noise in proton spectroscopy of the human calf muscle at 7 T using localized B1 calibrationEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Large variations of tip angle within a slice can lead to suboptimal pulse power optimization using standard techniques, which measure the average tip angle over a slice; this effect is especially pronounced at fields of 7 T and above. A technique was introduced that performed a volume-selective power optimization in less than 10 sec and automatically calibrates the radiofrequency pulses for subsequent spectroscopy scans. Using this technique, MR spectra were acquired in the human calf of seven healthy volunteers with a partial volume Tx/Rx coil. Increases in signal-to-noise ratio based upon the unsuppressed water signal be...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Maarten J. Versluis, Hermien E. Kan, Mark A. van Buchem, Andrew G. Webb Source Type: journals

Phase-unwrapping algorithm for translation extraction from spherical navigator echoesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Spherical navigator echoes have been shown to determine rigid-body rotation and translation simultaneously. Following the determination of rotation, translations are determined from the phase change between the baseline and transformed spherical navigator echoes. Because the measured phase change is limited in the interval (-[pi], [pi]), a phase-unwrapping algorithm is required to recover the true phase change in absolute values. The unwrapping algorithm presented in this article is based on a priori information about the true translation-induced phase-change function. The algorithm is verified using simulation and in vivo...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Junmin Liu, Maria Drangova Source Type: journals

Longitudinal analysis of MRI T2 knee cartilage laminar organization in a subset of patients from the osteoarthritis initiativeEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The purpose of this pilot study was to longitudinally quantify the T2 laminar integrity of knee cartilage in a subset of subjects with osteoarthritis from the Osteoarthritis Initiative at baseline, 1-year follow-up, and 2-year follow-up. Cartilage from 13 subjects was divided into six compartments and subdivided into deep and superficial layers. At each time point, mean T2 values in superficial and deep layers were compared. Longitudinal analysis included full-thickness mean T2, mean deep T2, mean superficial T2, mean T2 laminar difference, mean percentage T2 laminar difference, and two-dimensional measures of cartilage th...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Julio Carballido-Gamio, Gabrielle Blumenkrantz, John A. Lynch, Thomas M. Link, Sharmila Majumdar Source Type: journals

Change in the proton T1 of fat and water in mixtureEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This work describes observed changes in the proton T1 relaxation time of both water and lipid when they are in relatively homogeneous mixtures. Results obtained from vegetable oil-water emulsions, pork kidney and lard mixtures, and excised samples of white and brown adipose tissues are presented to demonstrate this change in T1 as a function of mixture fat fraction. As an initial proof of concept, a simpler acetone-water experiment was performed to take advantage of complete miscibility between acetone and water and both components' single chemical shift peaks. Single-voxel MR spectroscopy was used to measure the T1 of pre...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Houchun H. Hu, Krishna S. Nayak Source Type: journals

An expandable catheter loop coil for intravascular MRI in larger blood vesselsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The present study proposes a catheter system with an expandable coil etched on a polyimide foil. The catheter system combines the advantages of a small insertion diameter when the coil is rolled up in a protective carrier sheath with an increased signal-to-noise ratio (SNR) and penetration depth when the coil is pushed out. After imaging, the coil can be retracted into the sheath and folded back into the initial rolled-up configuration due to the tapered geometry of the carrier foil. The catheter system was tested on two healthy anesthetized pigs, including tracking and high-resolution intravascular imaging. To reduce arti...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Ann-Kathrin Homagk, Reiner Umathum, Matthias Korn, Marc-André Weber, Peter Hallscheidt, Wolfhard Semmler, Michael Bock Source Type: journals

Motion correction using an enhanced floating navigator and GRAPPA operationsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A method for motion correction in multicoil imaging applications, involving both data collection and reconstruction, is presented. The floating navigator method, which acquires a readout line off center in the phase-encoding direction, is expanded to detect translation/rotation and inconsistent motion. This is done by comparing floating navigator data with a reference k-space region surrounding the floating navigator line, using a correlation measure. The technique of generalized autocalibrating partially parallel acquisition is further developed to correct for a fully sampled, motion-corrupted dataset. The flexibility of ...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Wei Lin, Feng Huang, Peter Börnert, Yu Li, Arne Reykowski Source Type: journals

T2 relaxation time abnormalities in bipolar disorder and schizophreniaEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
There are substantial abnormalities in the number, density, and size of cortical neurons and glial cells in bipolar disorder and schizophrenia. Because molecule-microenvironment interactions modulate metabolite signals characteristics, these cellular abnormalities may impact transverse (T2) relaxation times. We measured T2 relaxation times for three intracellular metabolites (N-acetylaspartate + N-acetylaspartylglutamate, creatine + phosphocreatine, and choline-containing compounds) in the anterior cingulate cortex and parieto-occipital cortex from 20 healthy subjects, 15 patients with bipolar disorder, and 15 patients wit...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Dost Öngür, Andrew P. Prescot, J. Eric Jensen, Elizabeth D. Rouse, Bruce M. Cohen, Perry F. Renshaw, David P. Olson Source Type: journals

Magnetic field homogenization of the human prefrontal cortex with a set of localized electrical coilsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The prefrontal cortex is a common target brain structure in psychiatry and neuroscience due to its role in working memory and cognitive control. Large differences in magnetic susceptibility between the air-filled sinuses and the tissue/bone in the frontal part of the human head cause a strong and highly localized magnetic field focus in the prefrontal cortex. As a result, image distortion and signal dropout are observed in MR imaging. A set of external electrical coils is presented that provides localized and high-amplitude shim fields in the prefrontal cortex, with minimum impact on the rest of the brain when combined wit...
Source: Magnetic Resonance in Medicine - November 13, 2009 Category: Radiology Authors: Christoph Juchem, Terence W. Nixon, Scott McIntyre, Douglas L. Rothman, Robin A. de Graaf Source Type: journals

Online real-time reconstruction of adaptive TSENSE with commodity CPU/GPU hardwareEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Adaptive temporal sensitivity encoding (TSENSE) has been suggested as a robust parallel imaging method suitable for MR guidance of interventional procedures. However, in practice, the reconstruction of adaptive TSENSE images obtained with large coil arrays leads to long reconstruction times and latencies and thus hampers its use for applications such as MR-guided thermotherapy or cardiovascular catheterization. Here, we demonstrate a real-time reconstruction pipeline for adaptive TSENSE with low image latencies and high frame rates on affordable commodity personal computer hardware. For typical image sizes used in interven...
Source: Magnetic Resonance in Medicine - November 10, 2009 Category: Radiology Authors: Sébastien Roujol, Baudouin Denis de Senneville, Erkki Vahala, Thomas Sangild Sørensen, Chrit Moonen, Mario Ries Source Type: journals

High-resolution magnetic resonance angiography in the mouse using a nanoparticle blood-pool contrast agent.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
High-resolution magnetic resonance angiography is already a useful tool for studying mouse models of human disease. Magnetic resonance angiography in the mouse is typically performed using time-of-flight contrast. In this work, a new long-circulating blood-pool contrast agent-a liposomal nanoparticle with surface-conjugated gadolinium (SC-Gd liposomes)-was evaluated for use in mouse neurovascular magnetic resonance angiography. A total of 12 mice were imaged. Scan parameters were optimized for both time-of-flight and SC-Gd contrast. Compared to time-of-flight contrast, SC-Gd liposomes (0.08 mmol/kg) enabled improved sm...
Source: Magnetic Resonance in Medicine - November 9, 2009 Category: Radiology Authors: Howles GP, Ghaghada KB, Qi Y, Mukundan S, Johnson GA Tags: Magn Reson Med Source Type: journals

Online real-time reconstruction of adaptive TSENSE with commodity CPU/GPU hardware.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Adaptive temporal sensitivity encoding (TSENSE) has been suggested as a robust parallel imaging method suitable for MR guidance of interventional procedures. However, in practice, the reconstruction of adaptive TSENSE images obtained with large coil arrays leads to long reconstruction times and latencies and thus hampers its use for applications such as MR-guided thermotherapy or cardiovascular catheterization. Here, we demonstrate a real-time reconstruction pipeline for adaptive TSENSE with low image latencies and high frame rates on affordable commodity personal computer hardware. For typical image sizes used in inte...
Source: Magnetic Resonance in Medicine - November 9, 2009 Category: Radiology Authors: Roujol S, de Senneville BD, Vahala E, Sørensen TS, Moonen C, Ries M Tags: Magn Reson Med Source Type: journals

High-resolution magnetic resonance angiography in the mouse using a nanoparticle blood-pool contrast agentEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
High-resolution magnetic resonance angiography is already a useful tool for studying mouse models of human disease. Magnetic resonance angiography in the mouse is typically performed using time-of-flight contrast. In this work, a new long-circulating blood-pool contrast agent - a liposomal nanoparticle with surface-conjugated gadolinium (SC-Gd liposomes) - was evaluated for use in mouse neurovascular magnetic resonance angiography. A total of 12 mice were imaged. Scan parameters were optimized for both time-of-flight and SC-Gd contrast. Compared to time-of-flight contrast, SC-Gd liposomes (0.08 mmol/kg) enabled improved sm...
Source: Magnetic Resonance in Medicine - November 9, 2009 Category: Radiology Authors: Gabriel P. Howles, Ketan B. Ghaghada, Yi Qi, Srinivasan Mukundan Jr., G. Allan Johnson Source Type: journals

3D noncontrast MR angiography of the distal lower extremities using flow-sensitive dephasing (FSD)-prepared balanced SSFPEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In conclusion, FSD-prepared balanced steady-state free precession in conjunction with electrocardiography gating and image subtraction provides a promising noncontrast-MRA strategy for the distal lower extremities. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. (Source: Magnetic Resonance in Medicine)
Source: Magnetic Resonance in Medicine - October 30, 2009 Category: Radiology Authors: Zhaoyang Fan, John Sheehan, Xiaoming Bi, Xin Liu, James Carr, Debiao Li Source Type: journals

Characterizing and correcting gradient errors in non-cartesian imaging: Are gradient errors linear time-invariant (LTI)?Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Non-Cartesian and rapid imaging sequences are more sensitive to scanner imperfections such as gradient delays and eddy currents. These imperfections vary between scanners and over time and can be a significant impediment to successful implementation and eventual adoption of non-Cartesian techniques by scanner manufacturers. Differences between the k-space trajectory desired and the trajectory actually acquired lead to misregistration and reduction in image quality. While early calibration methods required considerable scan time, more recent methods can work more quickly by making certain approximations. We examine a ra...
Source: Magnetic Resonance in Medicine - October 29, 2009 Category: Radiology Authors: Brodsky EK, Samsonov AA, Block WF Tags: Magn Reson Med Source Type: journals

A 2D MTF approach to evaluate and guide dynamic imaging developments.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
As the number and complexity of partially sampled dynamic imaging methods continue to increase, reliable strategies to evaluate performance may prove most useful. In the present work, an analytical framework to evaluate given reconstruction methods is presented. A perturbation algorithm allows the proposed evaluation scheme to perform robustly without requiring knowledge about the inner workings of the method being evaluated. A main output of the evaluation process consists of a two-dimensional modulation transfer function, an easy-to-interpret visual rendering of a method's ability to capture all combinations of spati...
Source: Magnetic Resonance in Medicine - October 29, 2009 Category: Radiology Authors: Chao TC, Chung HW, Hoge WS, Madore B Tags: Magn Reson Med Source Type: journals

Improved technique for measurement of regional fractional ventilation by hyperpolarized (3)He MRI.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Quantitative measurement of regional lung ventilation is of great significance in assessment of lung function in many obstructive and restrictive pulmonary diseases. A new technique for regional measurement of fractional ventilation using hyperpolarized (3)He MRI is proposed, addressing the shortcomings of an earlier approach that limited its use to small animals. The new approach allows for the acquisition of similar quantitative maps over a shortened period and requires substantially less (3)He gas. This technique is therefore a better platform for implementation in large species, including humans. The measurements u...
Source: Magnetic Resonance in Medicine - October 29, 2009 Category: Radiology Authors: Emami K, Kadlecek SJ, Woodburn JM, Zhu J, Yu J, Vahdat V, Pickup S, Ishii M, Rizi RR Tags: Magn Reson Med Source Type: journals

3D noncontrast MR angiography of the distal lower extremities using flow-sensitive dephasing (FSD)-prepared balanced SSFP.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In conclusion, FSD-prepared balanced steady-state free precession in conjunction with electrocardiography gating and image subtraction provides a promising noncontrast-MRA strategy for the distal lower extremities. Magn Reson Med, 2009. (c) 2009 Wiley-Liss, Inc. PMID: 19877278 [PubMed - as supplied by publisher] (Source: Magnetic Resonance in Medicine)
Source: Magnetic Resonance in Medicine - October 29, 2009 Category: Radiology Authors: Fan Z, Sheehan J, Bi X, Liu X, Carr J, Li D Tags: Magn Reson Med Source Type: journals

Improved technique for measurement of regional fractional ventilation by hyperpolarized 3He MRIEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Quantitative measurement of regional lung ventilation is of great significance in assessment of lung function in many obstructive and restrictive pulmonary diseases. A new technique for regional measurement of fractional ventilation using hyperpolarized 3He MRI is proposed, addressing the shortcomings of an earlier approach that limited its use to small animals. The new approach allows for the acquisition of similar quantitative maps over a shortened period and requires substantially less 3He gas. This technique is therefore a better platform for implementation in large species, including humans. The measurements using the...
Source: Magnetic Resonance in Medicine - October 29, 2009 Category: Radiology Authors: Kiarash Emami, Stephen J. Kadlecek, John M. Woodburn, Jianliang Zhu, Jiangsheng Yu, Vahid Vahdat, Stephen Pickup, Masaru Ishii, Rahim R. Rizi Source Type: journals

A 2D MTF approach to evaluate and guide dynamic imaging developmentsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
As the number and complexity of partially sampled dynamic imaging methods continue to increase, reliable strategies to evaluate performance may prove most useful. In the present work, an analytical framework to evaluate given reconstruction methods is presented. A perturbation algorithm allows the proposed evaluation scheme to perform robustly without requiring knowledge about the inner workings of the method being evaluated. A main output of the evaluation process consists of a two-dimensional modulation transfer function, an easy-to-interpret visual rendering of a method's ability to capture all combinations of spatial a...
Source: Magnetic Resonance in Medicine - October 29, 2009 Category: Radiology Authors: Tzu-Cheng Chao, Hsiao-Wen Chung, W. Scott Hoge, Bruno Madore Source Type: journals

Characterizing and correcting gradient errors in non-cartesian imaging: Are gradient errors linear time-invariant (LTI)?Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Non-Cartesian and rapid imaging sequences are more sensitive to scanner imperfections such as gradient delays and eddy currents. These imperfections vary between scanners and over time and can be a significant impediment to successful implementation and eventual adoption of non-Cartesian techniques by scanner manufacturers. Differences between the k-space trajectory desired and the trajectory actually acquired lead to misregistration and reduction in image quality. While early calibration methods required considerable scan time, more recent methods can work more quickly by making certain approximations. We examine a rapid ...
Source: Magnetic Resonance in Medicine - October 29, 2009 Category: Radiology Authors: Ethan K. Brodsky, Alexey A. Samsonov, Walter F. Block Source Type: journals

Robust GRAPPA-accelerated diffusion-weighted readout-segmented (RS)-EPIEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Readout segmentation (RS-EPI) has been suggested as a promising variant to echo-planar imaging (EPI) for high-resolution imaging, particularly when combined with parallel imaging. This work details some of the technical aspects of diffusion-weighted (DW)-RS-EPI, outlining a set of reconstruction methods and imaging parameters that can both minimize the scan time and afford high-resolution diffusion imaging with reduced distortions. These methods include an efficient generalized autocalibrating partially parallel acquisition (GRAPPA) calibration for DW-RS-EPI data without scan time penalty, together with a variant for the p...
Source: Magnetic Resonance in Medicine - October 27, 2009 Category: Radiology Authors: Samantha J. Holdsworth, Stefan Skare, Rexford D. Newbould, Roland Bammer Source Type: journals

Sodium MRI using a density-adapted 3D radial acquisition technique.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A density-adapted three-dimensional radial projection reconstruction pulse sequence is presented which provides a more efficient k-space sampling than conventional three-dimensional projection reconstruction sequences. The gradients of the density-adapted three-dimensional radial projection reconstruction pulse sequence are designed such that the averaged sampling density in each spherical shell of k-space is constant. Due to hardware restrictions, an inner sphere of k-space is sampled without density adaption. This approach benefits from both the straightforward handling of conventional three-dimensional projection re...
Source: Magnetic Resonance in Medicine - October 26, 2009 Category: Radiology Authors: Nagel AM, Laun FB, Weber MA, Matthies C, Semmler W, Schad LR Tags: Magn Reson Med Source Type: journals

Initial results on in vivo human coronary MR angiography at 7 T.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Seven tesla (T) MR imaging is potentially promising for the morphologic evaluation of coronary arteries because of the increased signal-to-noise ratio compared to lower field strengths, in turn allowing improved spatial resolution, improved temporal resolution, or reduced scanning times. However, there are a large number of technical challenges, including the commercial 7 T systems not being equipped with homogeneous body radiofrequency coils, conservative specific absorption rate constraints, and magnified sample-induced amplitude of radiofrequency field inhomogeneity. In the present study, an initial attempt was made...
Source: Magnetic Resonance in Medicine - October 26, 2009 Category: Radiology Authors: van Elderen SG, Versluis MJ, Webb AG, Westenberg JJ, Doornbos J, Smith NB, de Roos A, Stuber M Tags: Magn Reson Med Source Type: journals

Disease state prediction from resting state functional connectivity.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The application of multivoxel pattern analysis methods has attracted increasing attention, particularly for brain state prediction and real-time functional MRI applications. Support vector classification is the most popular of these techniques, owing to reports that it has better prediction accuracy and is less sensitive to noise. Support vector classification was applied to learn functional connectivity patterns that distinguish patients with depression from healthy volunteers. In addition, two feature selection algorithms were implemented (one filter method, one wrapper method) that incorporate reliability informatio...
Source: Magnetic Resonance in Medicine - October 26, 2009 Category: Radiology Authors: Craddock RC, Holtzheimer PE, Hu XP, Mayberg HS Tags: Magn Reson Med Source Type: journals

Complex-valued analysis of arterial spin labeling-based functional magnetic resonance imaging signals.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Cerebral blood flow-dependent phase differences between tagged and control arterial spin labeling images are reported. A biophysical model is presented to explain the vascular origin of this difference. Arterial spin labeling data indicated that the phase difference is largest when the arterial component of the signals is preserved but is greatly reduced as the arterial contribution is suppressed by postinversion delays or flow-crushing gradients. Arterial vasculature imaging by saturation data of activation and hypercapnia conditions showed increases in phase accompanying blood flow increases.An arterial spin labeling...
Source: Magnetic Resonance in Medicine - October 26, 2009 Category: Radiology Authors: Hernandez-Garcia L, Vazquez AL, Rowe DB Tags: Magn Reson Med Source Type: journals

Delayed gadolinium-enhanced magnetic resonance imaging (dGEMRIC) of hip joint cartilage in femoroacetabular impingement (FAI): Are pre- and postcontrast imaging both necessary?Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The purpose of this study was to assess if delayed gadolinium MRI of cartilage using postcontrast T(1) (T(1Gd)) is sufficient for evaluating cartilage damage in femoroacetabular impingement without using noncontrast values (T(10)). T(1Gd) and DeltaR(1) (1/T(1Gd) - 1/T(10)) that include noncontrast T(1) measurements were studied in two grades of osteoarthritis and in a control group of asymptomatic young-adult volunteers. Differences between T(1Gd) and DeltaR(1) values for femoroacetabular impingement patients and volunteers were compared. There was a very high correlation between T(1Gd) and DeltaR(1) in all study group...
Source: Magnetic Resonance in Medicine - October 26, 2009 Category: Radiology Authors: Bittersohl B, Hosalkar HS, Kim YJ, Werlen S, Siebenrock KA, Mamisch TC Tags: Magn Reson Med Source Type: journals