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Simulation-based analysis of the resolution and SNR properties of partial k-space EPIEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In normal echo planar imaging (EPI) sequences, a long data acquisition time not only excessively attenuates the signal obtained from the sequence but also alters its resolution depending on the adjustment of the sequence. In conventional full echo mode, the image resolution is preserved because of the negative high frequency parts. However, signal to noise ratio (SNR) is poor because of attenuation of DC components. So, a new pulse sequence is designed for gradient echo-echo planar imaging (GE-EPI) to solve this problem. Instead of starting acquisition from the maximum point in k-Space, the acquisition point is selected ac...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 28, 2009 Category: Radiology Authors: Aamir Saeed Malik Source Type: journals

Inverse design of a phased-array coil for breast magnetic resonance imagingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Breast magnetic resonance imaging (MRI) is a very useful tool for human breast cancer detection and the advance of dedicated RF coil technology is essential for enhanced image quality. In this work, we propose an efficient, hybrid algorithm for the inverse design of a phased array coil for breast MRI. The design method starts with the specification of the desired RF (B1) field within a predefined region, using the so-called target-field technique, followed by a streamline function method to find the initial coil winding by discretizing the calculated continuous current density. Then, a deformation approach is used to furth...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 28, 2009 Category: Radiology Authors: Yu Li, Feng Liu, Ewald Weber, Bing Li, Stuart Crozier Source Type: journals

Digital multiband receiver for magnetic resonanceEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A multichannel, digital receiver made of off-the-shelf components is presented. The direct-sampling and software-based direct-conversion constitutes a flexible receiver platform for multinuclear MR applications. The architecture allows increased level of flexibility in the functionality of the receiver, also beyond MR imaging and spectroscopy applications. The system is designed in a way that the parallel operation with a standard MRI scanner does not require either hardware changes or specially designed pulse sequences. By using proper anti-alias filtering at the RF front-end, the system described can be applied for signa...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 28, 2009 Category: Radiology Authors: Pekka Sipilä, Rolf F. Schulte, Gerhard Wachutka, Florian Wiesinger Source Type: journals

Reducing MRI gradient coil vibration with rib stiffenersEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This work investigates the effect of rib stiffeners on the free and forced vibration of a gradient coil in a magnetic resonance imaging (MRI) scanner. Several reinforcement schemes are studied in this article. One scheme utilizes the existing holes in the gradient coil structure (typically reserved for magnetic shims) to produce the reinforcement. Nonferrous, nonmagnetic carbon fiber rib stiffeners are employed to fill these holes in several ways to strengthen a gradient coil. Another scheme replaces the inner half of the gradient coil material with a grid of interconnected axial and circumferential rib stiffeners. It is f...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 28, 2009 Category: Radiology Authors: Tian Ran Lin, Peter O'Shea, Chris Mechefske Source Type: journals

Quadrature radio frequency coil for magnetic resonance imaging of the wrist at 4TEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A magnetic resonance imaging (MRI) quadrature transmit/receive radio frequency (RF) coil for the purpose of imaging the human wrist in high resolution is outlined. The proposed design is used in a nonconventional manner within the bore of the MRI scanner. Due to restrictions of field linearity, space, and patient comfort, it was deemed necessary to design a coil that can be placed above the head with the arm aligned in the transverse plane of the magnet. This configuration allows the placement of the coil to be near the isocenter of the magnet, away from static field impurities. The RF wrist coil was built and a phantom st...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 1, 2009 Category: Radiology Authors: Ali Zailaa, Viktor Vegh, Don Maillet, Mark W. Strudwick Source Type: journals

Trap design for insertable second-nuclei radiofrequency coils for magnetic resonance imaging and spectroscopyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article presents the benefits of this method, specifically in this case for 31P imaging/spectroscopy, through modeling results, bench measurements, imaging, and spectra acquisition. The use of a resonant trap in conjunction with a modular design permitted the insertion of the phosphorus coil as an "add-on" into multiple existing proton coils, suggesting particular applicability in the high-field arena, where spectroscopy holds great promise, but where proton coil design complexity exists that is not easily re-engineered for dual-nuclei use. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Enginee...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 17, 2009 Category: Radiology Authors: Arash Dabirzadeh, Mary Preston McDougall Source Type: journals

Minimum stored energy MRI superconducting magnets: From low to high fieldEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The aim of this article is to describe superconducting magnet coil arrangements from low to high field, particularly from 1T to 7T, within the context of the minimum stored energy designs. The findings illustrate that at low field, the maximum peak magnetic fields are located away from the most inner coils of the magnet configuration, whereas in high field designs, the maximum peak magnetic fields are created on coils lying on the inner diameter of the magnet bore. This becomes a critical aspect of any high field design, since there appears to be much less freedom of design at higher fields, due to the inherent limitations...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 15, 2009 Category: Radiology Authors: Viktor Vegh, Quang M. Tieng, Ian M. Brereton Source Type: journals

Development of a QA phantom and protocol for proton magnetic resonance spectroscopyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The purpose of this study was to develop a special proton magnetic resonance spectroscopy (1H-MRS) phantom, to establish and verify a quality assurance (QA) protocol, and to perform QA for a MR system. For a complete QA protocol, seven principal quality factors (PQFs) were measured. For evaluation of localization and quantification accuracy, two PQFs which are difficult to measure in commercial phantoms, we developed the layered dumbbell-shaped phantom. The performance sensitivity of our phantom was determined as a function of the voxel size on three occasions over [sim]1 year. All MRS QA factors were optimized on two diff...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 15, 2009 Category: Radiology Authors: Dong-Cheol Woo, Chi-Bong Choi, Sang-Soo Kim, Hyang-Shuk Rhim, Geon-Ho Jahng, Hyeon-Man Baek, Orhan Nalcioglu, Bo-Young Choe Source Type: journals

Underground variations in BEarth: Implications for near-surface MRIEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This study addresses the practicality of using various magnitude static magnetic fields to perform near-surface imaging by focusing on the restrictions the magnetic field places on major aspects of the MRI procedure. Measurements of the magnitude and direction of the Earth's magnetic field were made as a function of depth down to 6 m at a test site. These values were used to simulate in situ magnetic resonance images arising from the water in the hydrated soil. Images show that the greatest limitation is spatial susceptibility variations that affect the static magnetic field used by the hypothetical system. Higher applied ...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 15, 2009 Category: Radiology Authors: Christina L. Bray, Joseph P. Hornak Source Type: journals

A wrapped edge transverse gradient coil design for increased gradient homogeneityEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A transverse gradient coil design is described for wire wound cylindrical applications. The proposed design is aimed for use as a fixed gradient coil or as an insertable gradient coil. Although we describe a transverse gradient coil for clinical MRI scanners, the principle could be applied for use in preclinical systems. The gradient coil wire wound return paths are altered to allow for the ends of the gradient coil to be wrapped into the transverse plane of the MRI system to reduce the effect of their contribution to the magnetic field within the FoV. In essence, this new configuration reduces the inductance of the coil b...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 15, 2009 Category: Radiology Authors: Viktor Vegh, Quang M. Tieng, Ian M. Brereton, Graham J. Galloway Source Type: journals

A passive dual-circulator based transmit/receive switch for use with reflection resonators in pulse electron paramagnetic resonanceEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
To protect the low-noise amplifier (LNA) in the receive arm of a pulsed 250 MHz EPR bridge, it is necessary to install as much isolation as possible between the power exciting the spin system and the LNA when high power is present in the receive arm of the bridge, while allowing the voltage induced by the magnetization in the spin sample to be passed undistorted and undiminished to the LNA once power is reduced below the level that can cause LNA damage. We discuss a combination of techniques to accomplish this involving the power-routing circulator in the bridge, a second circulator acting as an isolator with passive shunt...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 15, 2009 Category: Radiology Authors: Subramanian V. Sundramoorthy, Boris Epel, Colin Mailer, Howard J. Halpern Source Type: journals

Evaluating the accuracy and impact of registration in dynamic contrast-enhanced breast MRIEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article presents a quantitative evaluation framework - incorporating a novel heterogeneous biomechanical model - for objectively comparing the accuracy of registration algorithms in dynamic contrast-enhanced (DCE) MRI of the breast; an evaluation of several algorithms using this framework; and several clinical examples where accurate registration significantly changes the shape of the enhancement curves associated with suspicious regions of interest (ROIs) identified by a radiologist. The experimental results demonstrate: (i) the efficacy of the evaluation framework; (ii) that a good registration algorithm can accurat...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 20, 2009 Category: Radiology Authors: Andrew Hill, Andrew Mehnert, Stuart Crozier, Kerry McMahon Source Type: journals

Design, fabrication, and testing of an insertable double-imaging-region gradient coilEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We have constructed a small-bore insertable gradient coil with two linear gradient imaging regions and interfaced it with an MRI scanner. We have also constructed an RF system capable of transmitting or receiving in both regions simultaneously. Designs for conductor placement for two-region X-, Y-, and Z-gradient coils were optimized by simulated annealing. Wire patterns for each axis were chosen that gave low inductance, reasonable homogeneity over a large imaging volume and high efficiency (gradient field per-unit-current). Imaging was performed on a Siemens 3T TIM Trio scanner equipped with three additional gradient amp...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 20, 2009 Category: Radiology Authors: K. Craig Goodrich, J. Rock Hadley, Sung M. Moon, Blaine A. Chronik, Timothy J. Scholl, Joshua T. Debever, Dennis L. Parker Source Type: journals

Magnetic resonance imaging with composite (dual) gradientsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article presents the concept of dynamically selectable composite gradient systems where local gradients and whole body gradients can be selected independently and simultaneously. The relative performance of whole body, insert, and composite gradients is predicted for echoplanar, turbo spin echo, and steady state free precession. A realization of the concept is presented. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 35B: 89-97, 2009 (Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering)
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 20, 2009 Category: Radiology Authors: Dennis L. Parker, K. Craig Goodrich, J. Rock Hadley, Seong-Eun Kim, Sung M. Moon, Blaine A. Chronik, Ulrich Fontius, Franz Schmitt Source Type: journals

An independent multichannel imaging research system for ultrashort echo time imaging on clinical MR systemsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Most clinical magnetic resonance systems do not have access to ultrashort echo time (UTE) imaging. The aim of this project was to develop a fully independent imaging insert for clinical MR systems to provide this new research application without disturbing routine operation. The initial clinical target for the system was improved orthopedic upper limb imaging using ultrashort repeat and echo time acquisitions. Echo times as short as TE = 80 [mu]s were attained for standard 2DFT gradient echo sequences and TE = 25 [mu]s for asymmetrically sampled radial acquisitions using the 160 mm inside diameter symmetrical cylindrical i...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 20, 2009 Category: Radiology Authors: Martyn N.J. Paley, Eugeny Kryukov, Michael Lamperth, Ian R. Young Source Type: journals

Double spiral array coil design for enhanced 3D parallel MRI at 1.5 TeslaEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, an alternative volume array coil design for MR head imaging is presented. Superior to standard arrays, it provides smooth sensitivity variations in all three spatial dimensions. This is realized in form of a double-spiral phased-array coil, which consists of a +[pi] twisted inner and a -[pi] twisted outer array stacked together. This geometrical arrangement provides sufficient isolation between both single-spiral arrays allowing sufficient channel isolation. In this work, simulation results of the double-spiral conductor structure are presented demonstrating the smooth sensitivity variation in all three spat...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 20, 2009 Category: Radiology Authors: Matthias F. Mueller, Martin Blaimer, Felix Breuer, Titus Lanz, Andrew Webb, Mark Griswold, Peter Jakob Source Type: journals

A rapidly rotating RF coil for MRIEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article introduces a new concept for spin excitation and signal acquisition in magnetic resonance imaging (MRI) using rapid rotation of a single radiofrequency (RF) coil about a sample. A rotating RF coil system was constructed for 2 and 4.7 Tesla imaging. The acquired images of biological specimens were comparable to those of a conventional RF coil system. This approach may obviate the need for multiple channels and intricate RF decoupling of many coils, which impede the progress of multichannel array technology. It is hoped that hardware advantages of coil rotation and the additional parameter of rotational velocity...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 1, 2009 Category: Radiology Authors: Adnan Trakic, Bing Keong Li, Ewald Weber, Hua Wang, Stephen Wilson, Stuart Crozier Source Type: journals

A linear magnetic field scan driverEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article also gives a brief description of the field coils that are driven by the driver. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 35B: 44-58, 2009 (Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering)
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - February 12, 2009 Category: Radiology Authors: Richard W. Quine, Tomasz Czechowski, Gareth R. Eaton Source Type: journals

Reverse-engineering of gradient coil designs based on experimentally measured magnetic fields and approximate knowledge of coil geometry-application in exposure evaluationsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
For many MRI installations, the coil pattern that generates pulsed magnetic fields produced by gradient coils is not provided by the manufacturer. This has implications for accurate assessments of MRI worker exposures, which is currently an important topic of research. To correctly model the level of exposure, a full three-dimensional distribution of the magnetic field in the locality of the magnet end is required, which can be difficult to obtain by experimental measurements. This research presents one possible approach, in which the prediction of a current distribution that generates an approximately identical magnetic f...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - February 12, 2009 Category: Radiology Authors: Feng Liu, Adnan Trakic, Hector Sanchez Lopez, Qing Wei, Miguel Fuentes, Ewald Weber, Stuart Crozier Source Type: journals

Local bi-planar gradient array design using conformal mapping and simulated annealingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Many magnetic resonance imaging applications require high spatial and temporal resolution. The improved gradient performance required to achieve high spatial and temporal resolution may be achieved by using local gradient coils such as planar gradient inserts. The planar gradient set provides higher gradient performance because it is placed inside of the imaging bore of the magnet (within the body gradients) in close proximity to the imaging region. Although the wire patterns for planar gradients can be designed using two dimensional stream functions and simulated annealing, optimization of the two dimensional stream funct...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - February 12, 2009 Category: Radiology Authors: Sung M. Moon, K. Craig Goodrich, J. Rock Hadley, Dennis L. Parker Source Type: journals

Silicon cylinder spiral coil for nuclear magnetic resonance spectroscopy of nanoliter samplesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This contribution presents a new high sensitivity microdetector designed for high resolution proton NMR at 750 MHz (17.6 T) of sample volumes ranging from 5 to 40 nl. The desired volume of fluid is placed in a sealed 330/200 [mu]m outer/inner diameter glass capillary and is then situated in the center of the detection coil. The high quality factor detection coils are fabricated using silicon microtechnology. The materials from which the device is constructed are specially shaped to improve the homogeneity of the static magnetic field within the sample. Adverse effects of the finite, nonspherical sample geometry on the spec...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - February 12, 2009 Category: Radiology Authors: Stefan Leidich, Marco Braun, Thomas Gessner, Thomas Riemer Source Type: journals

Design and construction of a prototype high-power B0 insert coil for field-cycled imaging in superconducting MRI systemsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Field-cycled MRI provides a noninvasive quantification of the concentration of bound (activated) targeted contrast agents. For field-cycled imaging to be performed within a clinical full-body superconducting MRI magnet, an auxiliary insertable magnet is required that can dynamically change the main field strength during the MR pulse sequence. Herein, the design and construction of a solenoidal insert coil is discussed. Design aspects including active shielding, thermal performance, forces, and ramping times are examined. Proper materials, construction methods, and interfacing for the insert coil with a clinical MRI are als...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 1, 2008 Category: Radiology Authors: Jamu K. Alford, Timothy J. Scholl, William B. Handler, Blaine A. Chronik Source Type: journals

Actively decoupled transmit-receive coil-pair for mouse brain MRIEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A low-cost, high-performance RF coil-pair for MR imaging of mouse brain is described. A surface receiving coil is used for high spin-sensitivity, whereas a larger transmit coil, located outside the mouse holder, delivers good B1 uniformity across the brain with reasonable efficiency. The volume coil is constructed with an open architecture, making experimental setup easy and providing clear access to the head of the mouse. Each coil is switched between active and inactive modes using PIN diodes driven by a small amplifier external to the spectrometer. Because of this active decoupling, there is no requirement for orthogona...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 1, 2008 Category: Radiology Authors: Joel R. Garbow, Charlie Mcintosh, Mark S. Conradi Source Type: journals

In vivo MRI-based dental impression using an intraoral RF receiver coilEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The objective of this work was to develop a dedicated RF receiver coil for contrast-enhanced dental MRI which provides a high sensitivity in the region of the whole dental arch and allows for application of the contrast media into the mouth of the patient. To achieve this goal, an intraoral dental coil design with a built-in contrast medium applicator was developed and implemented. The coil was shown to enable high-resolution contrast-enhanced dental MRI in vivo. This was demonstrated on four teeth prepared for dental restorations. The average accuracy obtained for all four teeth was below 100 [mu]m. For two of the teeth, ...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 1, 2008 Category: Radiology Authors: O. Tymofiyeva, K. Rottner, D. Gareis, J. Boldt, F. Schmid, M.A. Lopez, E.-J. Richter, P.M. Jakob Source Type: journals

Inductively coupled RF coil design for simultaneous microimaging of multiple samplesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An apparatus for studying multiple samples simultaneously using magnetic resonance imaging was proposed. It consists of a number of individually resonant radiofrequency microcoils, each of which are inductively coupled to a larger transmit and receive coil. The advantages of this approach are ease of construction and coil replacement, if necessary, and the requirement for only one receive channel. Theoretical analysis based on equivalent circuit models has been performed, showing that when n microcoils are critically coupled to the larger coil, the signal-to-noise of each microsample decreases by a factor approximately equ...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 1, 2008 Category: Radiology Authors: Tao Wang, Luisa Ciobanu, Xiaozhong Zhang, Andrew Webb Source Type: journals

An inexpensive and programmable RF transmitter setup for two-coil CASLEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An inexpensive and programmable RF transmitter for two-coil continuous arterial spin labeling (CASL) system is presented in this article. Unlike previous implementations of two-coil CASL which require expensive MR RF instruments, our design utilizes a low-cost system on chip direct digital synthesizer and a mini-size communication RF power amplifier to generate the labeling RF waveform without sacrificing RF performance. Compared with a single RF channel two-coil CASL approach, this design requires minimal scanner hardware modifications. Moreover, this design offers a programmable interface for easy sequence setup and debu...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 1, 2008 Category: Radiology Authors: Qin Xu, Christopher Glielmi, Lei Zhou, Kisueng Choi, Xiaoping Hu Source Type: journals

Adaptively regularized gradient coils for reduced local heatingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Gradient and shim coil design is an inverse problem in which the objective is to generate a magnetic field with an error that falls within acceptable limits while optimizing some other property of the coil. This problem can be solved using a boundary element method via regularized matrix inversion. However, it is not possible to optimize properties that are not linear-least-squares with respect to the solutions using this method. In this work, we employ adaptive regularization to design coils with reduced maximum local current density, which is not a linear-least-squares problem. Reducing the maximum local current density ...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 1, 2008 Category: Radiology Authors: Michael Poole, Hector Sanchez Lopez, Stuart Crozier Source Type: journals

Simple modifications to the NMR PGSE technique for investigations in the regime of short diffusion observation timesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Simple modifications to the spin-echo NMR technique with pulsed magnetic field gradients are proposed. These modifications make it possible to compensate the negative influence of gradient pulse fronts by applying an additional gradient pulse, to eliminate the acoustic effect of gradient pulses on a sample by decoupling the probe and gradient coils, and to simplify the generation of bipolar gradient pulses of the magnetic field using a scheme of two electronic circuits. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 33B: 216-219, 2008 (Source: Concepts in Magnetic Resonance Part B: Magn...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 1, 2008 Category: Radiology Authors: A.V. Anisimov, E.A. Mishagina, N.R. Dautova Source Type: journals

An accurate simulator for magnetic resonance coil sensitivity estimationEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Coil sensitivity estimation in magnetic resonance experiments requires the knowledge of biological sample-induced resistance. In dependence on system geometry, many authors studied sample-coil interaction by using a very simple coil geometry (circular, square, etc.) and homogeneous infinitely long cylinders, spheres, or half-spaces as approximations of the sample geometry. However, in real MR experiments, both shape and dimensions can be very different with respect to these coil and sample models. In this article, we propose the application of finite-difference time-domain method for sample-induced resistance estimation. T...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 1, 2008 Category: Radiology Authors: Giulio Giovannetti, Vittorio Viti, Yongjun Liu, Wenhua Yu, Raj Mittra, Luigi Landini, Antonio Benassi Source Type: journals

A multifrequency narrow band-pass filterEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A highly selective, high-power, multifrequency band-pass filter is presented. The construction of the filter is based on multifrequency tuned resonators used in magnetic resonance experiments. High values of the radio-frequency resonators' quality factors enable construction of highly selective band-pass filters. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 33B: 145-151, 2008 (Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering)
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 11, 2008 Category: Radiology Authors: Vyacheslav Volotovskyy, Marco L.H. Gruwel, Barbara Blasiak, Boguslaw Tomanek Source Type: journals

A design of permanent magnet array for unilateral NMR deviceEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We have designed a three-dimensional magnetic circuit consisting of various pieces of magnetic blocks for a unilateral MRI device, which generates a homogeneous magnetic flux density at a remote region. The direction of the remanent flux density of the main outer magnetic blocks is parallel to the surface of the device; hence the direction of the magnetic flux density in the remote region is also parallel to the surface of the device. The magnitudes of the remanent flux density of the magnetic blocks are adjusted so as to minimize the variation of the magnetic flux density in the remote region. This magnetic circuit, with ...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 10, 2008 Category: Radiology Authors: Hirokazu Kato, Kanji Kishi, Norio Takahashi, Jun-Ichi Asaumi, Yasutoshi Honda, Yoshinobu Yanagi, Masaaki Aoki Source Type: journals

Effect of reduced pressure on the polarization of 129Xe in the production of hyperpolarized 129Xe gas: Development of a simple continuous flow mode hyperpolarizing system working at pressures as low as 0.15 atmEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The effect of reduced pressure on the polarization of 129Xe has been examined in batch and continuous flow modes aiming at developing a simple and convenient hyperpolarizing system. The effect of foreign gases was found to show a different tendency at reduced pressure as low as 0.15 atm compared to that near atmospheric pressure. For example, 129Xe polarization in binary mixtures of Xe and N2 was larger than that observed in ternary mixtures of Xe, N2, and 4He when compared with the same Xe content, and the highest polarization of 63.6% was given by the 5% Xe + 95% N2 mixture in the batch mode. The most noticeable result i...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 10, 2008 Category: Radiology Authors: Hirohiko Imai, Junko Fukutomi, Atsuomi Kimura, Hideaki Fujiwara Source Type: journals

RF coil loading measurements between 1 and 50 MHz to guide field-cycled MRI system designEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Conventional magnetic resonance imaging (MRI) uses a single superconducting magnet both to polarize the nuclear magnetic moments in a sample and to provide the magnetic field environment under which an image is acquired. In field-cycled MRI (FCMRI), these two tasks are independently accomplished by two actively controlled resistive magnets. As a result, the expressions for signal-to-noise ratio for an FCMRI system, as with other systems making use of prepolarization techniques (such as hyperpolarized noble gas MRI), are fundamentally different than those of a conventional system. Once losses in the receiver coil are domina...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 10, 2008 Category: Radiology Authors: K.M. Gilbert, T.J. Scholl, B.A. Chronik Source Type: journals

A versatile high speed 250-MHz pulse imager for biomedical applicationsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A versatile 250-MHz pulse electron paramagnetic resonance (EPR) instrument for imaging of small animals is presented. Flexible design of the imager hardware and software makes it possible to use virtually any pulse EPR imaging modality. A fast pulse generation and data acquisition system based on general purpose PCI boards performs measurements with minimal additional delays. Careful design of receiver protection circuitry allowed us to achieve very high sensitivity of the instrument. In this article, we demonstrate the ability of the instrument to obtain three-dimensional (3D) images using the electron spin echo (ESE) and...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 10, 2008 Category: Radiology Authors: Boris Epel, Subramanian V. Sundramoorthy, Colin Mailer, Howard J. Halpern Source Type: journals

Single-point Dixon water-fat imaging using 64-channel single-echo acquisition MRIEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article presents a method for high-speed water-fat imaging using Single-Echo Acquisition (SEA) with an array of 64 localized coil elements and single-point Dixon sequence. The method forms two-dimensional separate water and fat images from a single echo data. Specifically, a channel correlation and region-growing algorithm were developed to extract the phase information from the single echo data, eliminating the need for multiple data acquisition normally required for water/fat separation. Phantom studies on a 4.7 T scanner show that the method can handle large interchannel and cross-channel phase variations, even at ...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 10, 2008 Category: Radiology Authors: Jong Bum Son, Steven M. Wright, Jim X. Ji Source Type: journals

Immobilization using dental material casts facilitates accurate serial and multimodality small animal imagingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We present the use of vinyl polysiloxane dental impression material for immobilization of mice for imaging. Four different materials were examined to identify any potential artifacts using magnetic resonance techniques. A water phantom placed inside the cast was used at 4.7 T with magnetic resonance imaging and showed no effect at the center of the image when compared with images without the cast. A negligible effect was seen near the ends of the coil. Each material had no detectable signal using electron paramagnetic resonance imaging at 9 mT. The use of dental material also greatly enhances the use of fiducial markers th...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 8, 2008 Category: Radiology Authors: Chad R. Haney, Xiaobing Fan, Adrian D. Parasca, Gregory S. Karczmar, Howard J. Halpern, Charles A. Pelizzari Source Type: journals

A variable field strength system for hyperpolarized noble gas MR imaging of rodent lungsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Hyperpolarized Noble Gas (HNG), 3He (helium) or 129Xe (xenon), MR imaging has become a promising approach for visualizing lung anatomy and function. It has been theoretically predicted that low field strengths (0.05-0.2 T) may provide optimal signal-to-noise ratio (SNR) and spatial resolution for clinical HNG MR imaging. These optimum field strengths correspond to frequencies between 1.62-6.5 MHz and 0.59-2.35 MHz for 3He and 129Xe respectively. The optimum field strength depends on the size and geometry of the sample and radiofrequency (RF) coil as well as the field dependence of the HNG MR properties in the lung (e.g., r...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 8, 2008 Category: Radiology Authors: William Dominguez-Viqueira, Juan Parra-Robles, Matthew Fox, William B. Handler, Blaine A. Chronik, Giles E. Santyr Source Type: journals

Studies on multiple-quantum magic-angle-spinning NMR of half-integer quadrupolar nuclei under strong rf pulses with a microcoilEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In multiple-quantum magic-angle-spinning (MQMAS) NMR experiments, it has been argued that one should use as strong rf irradiation as possible in most situations so as to attain the better sensitivity. In this work, we theoretically derive formulas for the efficiency of MQMAS experiments for spin nuclei under strong rf irradiation, and experimentally examine the validity of the derived formulas. For this purpose, a microcoil was accommodated to magic-angle-spinning (MAS) experiments by developing a microcoil-based, coin-sized probe, which is attachable to an existing MAS module. The rf intensity of up to [sim]1 MHz was real...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 8, 2008 Category: Radiology Authors: Munehiro Inukai, Kazuyuki Takeda Source Type: journals

Design of a ceramic dielectric resonator for NMR microimaging at 14.1 teslaEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Radiofrequency coil design for magnetic resonance becomes increasingly challenging at high magnetic field strengths due to resonator dimensions being a significant fraction of the electromagnetic wavelength, as well as the increased radiative and component losses intrinsic to higher frequencies. In this article an inductively fed dual-disk ceramic dielectric resonator was constructed from barium strontium titanate, which has a high relative permittivity of 323, for operation at 600 MHz (14.1 tesla). The design is very simple, avoids wavelength issues, uses high Q-materials, and has the additional advantage of being able to...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 8, 2008 Category: Radiology Authors: T. Neuberger, V. Tyagi, E. Semouchkina, M. Lanagan, A. Baker, K. Haines, A.G. Webb Source Type: journals

A microstrip helmet coil for human brain imaging at high magnetic fieldsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A novel helmet coil for magnetic-resonance (MR) investigations of the human brain is described. It is based on a pure microstrip transmission-line (MTL) design. The coil consists of thin strip conductors (Cu) on a curved, low-loss dielectric material (polypropylene) generating an overall domelike structure. The design concept exploits the combination of the field profile generated by the current distribution along each MTL that is modified by termination and the geometric profile due to the curved MTL shape. Because of the semiopen transmission-line structure, most of the electromagnetic energy is stored in the dielectric ...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 8, 2008 Category: Radiology Authors: Wolfgang Driesel, Toralf Mildner, Harald E. Möller Source Type: journals

NMR microscopy with isotropic resolution of 3.0 [mu]m using dedicated hardware and optimized methodsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Nuclear magnetic resonance microscopy at an isotropic resolution of 3.0[mu]m was realized by using dedicated hardware such as RF surface microcoils, a planar triple-axis gradient with 6,500 G/cm, and a static magnetic field of 18.8 T. Purely phase-encoded constant time imaging was used to allow increasing the gradient strength for the suppression of diffusion effects without reducing the signal-to-noise ratio. For this method the relationship between gradient strength and true spatial resolution was investigated, and an empirical formula is provided that is useful for practical applications. The characteristics of the diff...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 8, 2008 Category: Radiology Authors: Markus Weiger, Daniel Schmidig, Schimun Denoth, Charles Massin, Franck Vincent, Michael Schenkel, Michael Fey Source Type: journals

B1 inhomogeneity effect reduction for 2D spatial selective RF pulse using simulated annealingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, a new RF pulse design method is proposed, which combines the simulated annealing (SA) algorithm and the k-space method to attain a pulse which can compensate the RF field inhomogeneity effect. The RF pulse envelope is firstly initiated using the k-space method and a cost function which contains the passband error and stopband error is defined. Then the SA is applied to refine the RF pulse shape to achieve low-cost value. Finally, under inhomogeneous RF field an optimized RF pulse with improved flip angle accuracy can be obtained. Simulation results show that when compared with the pulse designed only using t...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - April 1, 2008 Category: Radiology Authors: Yong Pang, Gary X. Shen Source Type: journals

Efficient method for parameter estimation of MRS signal using decimation and prior knowledgeEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Magnetic resonance spectroscopy (MRS) signals are often characterized by a low signal-to-noise ratio and overlapping peaks. Under these circumstances simple signal processing methods are not adequate. Using the different decimated sequences of original MRS signal and prior knowledge of frequency differences and equal damping factors, an efficient parameter estimation method is presented in this article. The experimental results show that among three parameter estimation methods of HTLS, HTLSPK ([Delta]fdeq) and the novel method, the last method obviously has the best performance with a lowest failure rate and a highest est...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 30, 2007 Category: Radiology Authors: Weiming Zeng Source Type: journals

Design and performance of a DNP prepolarizer coupled to a rodent MRI scannerEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We describe a 3.35 T DNP/9.4 T MRI installation based on a continuous-flow cryostat, using a standard wide-bore low-field NMR magnet as prepolarizer magnet and a widely available radical as polarizing agent. The interfacing to a rodent scanner requires that the infusion of the polarized solution in the animal be remotely controlled, because of limited access inside the magnet bore. Physiological constraints on the infusion rate can be a serious source of polarization loss, and the discussion of efficiency is therefore limited to that of the prepolarizer itself, i.e., the spin temperatures obtained in the solid state. To pu...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 30, 2007 Category: Radiology Authors: A. Comment, B. van den Brandt, K. Uffmann, F. Kurdzesau, S. Jannin, J.A. Konter, P. Hautle, W.Th. Wenckebach, R. Gruetter, J.J. van der Klink Source Type: journals

Modal analysis of a multilayered gradient coil insert in a 4-T MRI scannerEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The objective of this article is to characterize the dynamic behavior of a real (multilayered) gradient coil insert in a 4-T MRI scanner (from 200 to 3,000 Hz). The simply supported (assembly condition) and free-free (modal testing) condition are investigated in the dynamic analysis. In-situ vibration testing, modal testing, and numerical analyses are applied to uncover the dynamic features. The results indicate that bending modes in combination with different specific free-free and simply supported radial mode shapes provide the fundamental characteristics of the dynamic behavior of the gradient coil cylinder in the frequ...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 30, 2007 Category: Radiology Authors: Fenglin Wang, Chris Mechefske Source Type: journals

An analytical approach to the design of quiet cylindrical asymmetric gradient coils in MRIEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We present a simplified linearized model for the deflection of the coil due to electromagnetic forces, which is amenable to solution using analytical methods. Closed-form solutions for the coil deflection and the pressure pulse and noise level within the coil are obtained. These are used to design new coil winding patterns so as to reduce the acoustic noise. Sample results are shown both for unshielded and shielded gradient coils. Extensions of this model are indicated, although it is suggested that the advantages of the present closed-form solutions might then not be available, and fully numerical solutions may be needed ...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 30, 2007 Category: Radiology Authors: Lawrence K. Forbes, Michael A. Brideson, Stuart Crozier, Peter T. While Source Type: journals

Design and evaluation of a low field system for hyperpolarized 3-He gas imaging of neonatal lungsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
3-Helium can be optically pumped with laser light to produce exceptionally high nuclear polarization, which is independent of field strength. This increased polarization can allow imaging at low and ultra low field strengths, while still obtaining high signal-to-noise ratio. Low field magnets can be built for a fraction of the cost of high field clinical scanners and feature greatly reduced susceptibility artifact and less RF power requirement than higher field systems. Further advantage can be achieved by combination of hyperpolarized gas with parallel imaging methods. A particularly promising target for 3-He imaging is t...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 30, 2007 Category: Radiology Authors: E. Krjukov, S. Fichele, J.M. Wild, M.N.J. Paley Source Type: journals

A 19F and 1H goniometric split-millicoil NMR probe for solid-state NMREmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
To allow for single-crystal nuclear magnetic resonance (scNMR) investigations, an existing narrow bore high-field double-resonance millicoil 19F and 1H solid-state NMR probe was modified by adding a goniometer stage to the top. The goniometer was kept outside of the radiofrequency (RF) transceiver coil for improved filling factor and probe sensitivity. Because of the large size of single crystal grown, the transceiver coil was changed from a standard millicoil to a split-millicoil, or crude helmholtz coil, design with effects on probe performance further studied herein. The type of goniometer and crystal sample holder chos...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - October 1, 2007 Category: Radiology Authors: Jeffrey S. Devries, Xingang Zhao, Brian D. Sykes Source Type: journals

SAR simulation and the effect of mode coupling in a birdcage resonatorEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The issues related to the simulation of specific absorption rate (SAR) in a high frequency magnetic resonance coil are discussed in this work. Using simulation results, it is shown that the effect of the nonimaging modes on SAR can be substantial and thus must be taken into account. Also a technique for the estimation of SAR for coils with complicated geometry is presented. The presented technique will be useful in cases where the conventional finite difference time domain simulation is not practical because of large memory requirement and/or excessively long computation time. © 2007 Wiley Periodicals, Inc. Concepts Magn ...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 10, 2007 Category: Radiology Authors: S. Reza, S. Vijayakumar, M. Limkeman, F. Huang, C. Saylor Source Type: journals

The sphere in a uniform RF field - RevisitedEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We consider eddy current generation in weakly conducting spheres as a means to characterize RF power dissipation over the frequency range 0.1-1.2 MHz, which is relevant to MRI in very low magnetic fields. We provide a complete, yet simple, theoretical analysis of the homogeneous sphere in a uniform RF field and summarize expressions for the current density, power dissipation, and magnetic field for the limiting case of the nonmagnetic conducting sphere. Experiments are performed on spherical saline phantoms using a whole-body B1-coil as the RF field source. Changes in the quality factor and magnetic field profile of the co...
Source: Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering - July 9, 2007 Category: Radiology Authors: C.P. Bidinosti, E.M. Chapple, M.E. Hayden Source Type: journals