|Receive Concepts & Arrays|
Traveling Wave MR on a Whole-Body System
David Otto Brunner1, Nicola De Zanche1, Jan Paska, Juerg Fröhlich, Klaas Paul Pruessmann1
1University and ETH Zurich, Zurich, Switzerland
With increasing frequencies of MR systems, RF probe design becomes significantly more difficult due to shrinking wave length. The resulting RF fields become more inhomogeneous and the area of efficient reactive coupling to the spins becomes smaller. Hence we propose to abandon near field coupling in MR probe design and rely on propagating field coupling realized by traveling waves. The effectiveness, feasibility and advantages of this approach are demonstrated by high-resolution images as well as whole-body images at 7T taken from phantoms placed 65 cm a way from the RF probe showing excellent SNR and image homogeneity.
|Non-Resonant Microstrip (NORM) RF Coils: An
Unconventional RF Solution to MR Imaging and Spectroscopy
Xiaoliang Zhang1, 2, Chunsheng Wang1, Zhentian Xie1, Bing Wu1
1University of California San Francisco, San Francisco, USA; 2UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco & Berkeley, USA
A non-resonant RF coil technique for MR imaging and spectroscopy is proposed. This technique can dramatically simplify the conventional RF coil design and overcome numerous technical difficulties in designing high frequency coils, multiple tuned coils and parallel imaging coil arrays. MR sensitivity comparison with a conventional resonant coil shows the reception efficiency or MR sensitivity of the non-resonant coil is comparable with that of the conventional resonant coil. Because of the non-resonance property, a non-resonant coil can be used for all kinds of NMR sensitive nuclei at all kinds of different field strengths.
A 6-Element Coil Array for Parallel
Imaging in Arbitrary Directions
Matthias Korn1, Reiner Umathum1, Sven Müller1, Wolfhard Semmler1, Michael Bock1
1Deutsches Krebsforschungszentrum (dkfz), Heidelberg, Germany
A 6-channel rf-coil array for small-animal imaging at clinical 3T MRI systems is presented. Two coil-arrays each consisting of a loop, a butterfly and a saddle-train-coil side by side were build and assembled to form a 6-channel array. Due to position and geometry the elements have orthogonal sensitivity profiles and low mutual coupling. MR experiments were performed showing the applicability of the setup for parallel imaging with encoding in arbitrary directions.
16-Channel Microstrip Array Using 1st and 2nd
Harmonics for Parallel Imaging at 7T
Bing Wu1, Chunsheng Wang1, Zhentian Xie1, Xiaoliang Zhang1, 2
1UCSF, San Francisco, California , USA; 2UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco & Berkeley, California , USA
High field parallel imaging, as a promising imaging modality, offers high spatial resolution and high temporal resolution simultaneously. However, design of required high frequency parallel RF coil arrays, especially dense-spaced human coil arrays, faces many daunt technical challenges in attaining sufficient EM decoupling, image homogeneity and better geometry factors (g-factor). In this work, we propose a novel technique for the array design using the 1st and 2nd harmonics of microstrip resonators. This technique provides improved image homogeneity, intrinsic element-decoupling that allows of increased channel number, and better parallel imaging performance with reduced g-factor, Based on the proposed technique, a 16-ch microstrip array with alternatively placed 1st and 2nd harmonic resonance elements was designed and tested for 7T parallel imaging applications.
Tic Tac Toe: Highly-Coupled, Load Insensitive Tx/Rx
Array and a Quadrature Coil Without Lumped Capacitors
Tamer S. Ibrahim1, YiK-Kiong Hue1, Ryan Gilbert1, Fernando E. Boada1
1University of Pittsburgh, Pittsburgh, Pennsylvania, USA
This work presents a new coil design, Tic-Tac-Toe, that is highly load insensitive (negate high-field/frequency electromagnetic effects), yet is highly coupled (utilizes inherent SNR properties associated with coupled coils.) The Tic-Tac-Toe was successfully tested as a transmit/receive array and as a standard 4-port quadrature coil at 7 tesla.
An 8-Channel Array Adapted for Pediatric Cardiac
Thomas Grafendorfer1, Frandics Pak Chan2, Greig Scott2, Richard A. Barth2, Roland Bammer2
1GE Healthcare, Stanford, California , USA; 2Stanford University, Stanford, California , USA
One of the major shortcomings of pediatric cardiac MRI is the lack of appropriate coils leading to makeshift solutions with adult coils that yield suboptimal SNR and mediocre parallel imaging support. In fact, it is not uncommon that the size of one element of an adult array coil is larger than the width of the chest of a pediatric patient. That said, the availability of parallel imaging would be of utmost importance for these exams as these patients usually have significantly higher heart rates, are less compliant for breath-hold scans or should not be kept too long under general anesthesia due to their already very unstable clinical condition.
A 128-Channel Helium-3 Phased Array at 3T
for Highly Accelerated Parallel Imaging in Hyperpolarized Gas MRI
Ray F. Lee1, Hugo Chang2, Cornel Stefanescu3, Bernd Stoeckel2, Davide Santoro3, Debra Strick4, Rong Xue3, Niels Oessingman2, Glyn Johnson3, Daniel Sodickson3
1Princeton University, Princeton, New Jersey, USA; 2Siemens Medical Solution USA, New York, New York, USA; 3New York Unviersity Medical Center, New York, New York, USA; 4University of California Los Ageles, Los Angeles, California , USA
A 128-ch Helium-3 coil array at 3T was developed to take advantage of parallel imaging with hyperpolarized gas in lung MRI. The large number coil array enables us to study that at which acceleration factor, the SNR benefits from both hyper-polarization and under-sampling in non-equilibrium state are neutralized by the increasing g-factor. Five volunteers have been scanned with this coil using 2D GRE sequence with iPAT 1, 4, and 8. No appreciable SNR difference between iPAT 1 and 4 was found. The results with iPAT=8 produced the first evidence that the image integrity can be well preserved at high acceleration factor.
Flexible Microcoils for In-Vivo Biliary Imaging
Munir Ahmad1, Warren Casperz2, Ian Young1, Simon Taylor-Robinson2, Richard Syms1, Wady Gedroyc2
1Imperial College London, London, UK; 2St Mary”¦s Hospital, Imperial Research NHS Trust, London, UK
A detector coil is described for use with an MR-compatible biliary endoscope. The coil has to pass down through a 3.2mm diameter channel, then turn through a right angle before being passed along the bile duct for 50mm or more. The coil is designed for high resolution imaging. Silicon semiconductor manufacturing techniques have been used in its manufacture, with the silicon, which is very brittle and inflexible, and is not at all biocompatible, being removed at the end to leave a copper coil embedded in plastic. Phantom images which show its current performance are shown.
Coil Geometry Optimization for Better SNR and
George Carlos do Nascimento1, Shumin Wang1
1National Institutes of Health, Bethesda, USA
The restricted clearance space for arrays coils for animals imposes significant limitations and difficulties to avoid strong mutual couplings. We present a study of coil geometries for improved SNR. Loops made with circular wires were compared with a circular flat strip and with a circular loop. By using the Surface Integral Equation method, coils with different sizes were simulated, and as a result, coils were optimized. Experimental evaluation of these coils was realized by MRI. In particular, a cylinder shaped coil shows a better profile for the field map, better SNR and also less coupling to the neighbor loop coil.
Cryogenic Varactor-Tuned 4-Element Array and Cryostat
for µ-MRI of Trabecular Bone in the Distal Tibia
Jarek Wosik1, Krzysztof Nesteruk2, Maged R. Kamel1, Flora Ip1, Lian Xue1, Alexander C. Wright3, Felix W. Wehrli3
1University of Houston, Houston, USA; 2Institute of Physiscs Polish Academy of Sciences, Warsaw, Poland; 3University of Pennsylvania Medical Center, Philadelphia, USA
We report on the development of a clinically practical cryogenic array and cryostat assembly for use in a 3 T MRI scanner to provide increased SNR in µ-MRI studies of trabecular bone in the distal tibia. Both cryogenic copper and superconducting (HTS) materials are explored. Each array element is a double-layer rotated split copper ring, separated by 0.5 mm dielectric. A plastic liquid nitrogen cryostat was custom made to integrate with remotely controlled varactor-based tuning/matching/decoupling circuitry. Performance of the array is under investigation and more than two-fold SNR gain is expected, confirmed by gains obtained on a single element.