Joint Annual Meeting ISMRM-ESMRMB 2014 10-16 May 2014 Milan, Italy

RF Arrays & Related Technology

Wednesday 14 May 2014
Yellow 1, 2 & 3  13:30 - 15:30 Moderators: Gregor Adriany, Ph.D., Ryan J. Brown, Ph.D.

13:30 0617.   The ultimate SNR and SAR in realistic body models
Bastien Guerin1, Jorge F Villena2, Athanasios G Polimeridis2, Elfar Adalsteinsson2,3, Luca Daniel2, Jacob White2, and Lawrence L Wald1,3
1A. A. Martinos Center for Biomedical Imaging, Dpt. of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 2Dpt. of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 3Division of Health Sciences Technology, Harvard-MIT, Cambridge, MA, United States

The ultimate SNR (uSNR) and SAR (uSAR) have been computed in uniform spheres and cylinders. These ultimate metrics have been useful to rank coils with respect to the ultimate performance and to suggest design modifications. However the performance of parallel imaging and the computation of SAR are strongly affected by the geometry of the head and the non-uniform distributions of the conductivity and permittivity in vivo. We compute for the first time the uSNR and USAR in complex, non-uniform body models and use these metrics to assess the performance of receive (transmit) arrays with up to 128 (16) channels.

13:42 0618.   Is a “one size fits all” many-element bore-lining remote body array feasible for routine imaging?
Daniel K. Sodickson1,2, Bei Zhang3, Qi Duan4, Ryan Brown1, Riccardo Lattanzi1,2, Karthik Lakshmanan1, Manuskha V. Vaidya1,2, Alicia Yang1,2, Robert Rehner5, Markus Vester5, Stefan Popescu5, Stefan Biber5, Bernd Stoeckel6, Hugo Chang6, and Graham C. Wiggins1
1Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 2The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States, 3Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States, 4Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States,5Siemens Healthcare, Erlangen, Germany, 6Siemens Medical Solutions, New York, NY, United States

If a many-element RF coil array could be mounted behind the scanner covers while preserving much of the SNR performance of close-fitting arrays, the benefits for patient comfort and simplicity of workflow would be dramatic. In numerical simulations and experimental evaluations of progressively larger encircling prototypes, we explored the feasibility of remote body array designs. Smaller-scale models performed well as compared with close-fitting counterparts. However, with a 50cm-diameter 124-element prototype, we encountered unexpected practical challenges, most notably relating to preamplifier noise coupling, which becomes significant in lightly-loaded many-element arrays. Effective remote array designs will have to contend with these challenges.

13:54 0619.   In-Bore Broadband Array Receivers with Optical Transmission
Jonas Reber1, Josip Marjanovic1, David Otto Brunner1, Thomas Schmid1, Urs Moser1, Benjamin Emanuel Dietrich1, Christoph Barmet1,2, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, 2Skope Magnetic Resonance Technologies, Zurich, Switzerland

The increasing need for RF acquisition channel counts from receiver coil arrays but also applications such as field monitoring, RF safety surveillance of parallel transmit systems and other applications make cable routing and its implications for patient comfort, system handling and safety a cumbersome task. Further ultra-high field system push the frequency span of which the receiver has to be able to operate with. A novel platform is presented with broadband sampling ADCs communicating via digital high speed optical links to a host. It was found that the performance of rack mounted system can be matched at tolerable power consumptions.

14:06 0620.   
A three-layered coil arrangement for sodium imaging of the human brain at 9.4T
G Shajan1, Christian Mirkes1,2, Jens Hoffmann1, Klaus Scheffler1,2, and Rolf Pohmann1
1Max Planck Institute for Biological Cybernetics, Tuebingen, Baden Wuerttemberg, Germany, 2Department of Biomedical Magnetic Resonance, University Hospital, Tuebingen, Baden Wuerttemberg, Germany

Dual tuned coils, often used for X-nuclei imaging, compromise coil performance at both frequencies. Moreover, to acquire proton reference image covering the whole brain at 400 MHz, conventional dual tuned birdcage cannot be used due to wavelength effects. A combination of three coil arrays was developed to maximize the receive sensitivity at the sodium frequency and to provide proton signal covering the whole brain for anatomical localization and B0 off-resonance correction.

14:18 0621.   
A 7T 8 channel transmit-receive dipole array for head imaging: dipole element and coil evaluation
Gang Chen1, Martijn Cloos1, Daniel Sodickson1, and Graham Wiggins1
1The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States

Electric dipole antennas are seeing increasing use for 7T MR imaging. With 8 elements surrounding a body sized tissue equivalent phantom and array of dipole antennas can achieve higher central SNR than an array of loops, while simultaneously having greater coverage along Z. Most 7T head coils today rely on birdcage, TEM volume coils, or arrays of loops for transmit. Signal dropout in inferior brain regions such as the cerebellum and brain stem is a common problem. We describe here a dipole array for 7T head imaging designed for extended coverage and evaluate its performance in phantom and volunteer imaging.

14:30 0622.   Tranceive Phased Array with high Transmit Performance for Human Brain Application at 9.4 T
Nikolai I. Avdievich1, Andreas Pfrommer1, Jens Hoffmann1, Grzegorz L. Chadzynski1,2, Klaus Scheffler1, and Anke Henning1,3
1Max Planck Institute for Biological Cybernetics, Tübingen, Germany, 2Department of Biomedical Magnetic Resonance, University Hospital Tübingen, Tübingen, Germany, 3Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Surface loop phased arrays have been shown to improve transmit performance and B1 homogeneity for head imaging up to 9.4T. However, transmit arrays enlarged to fit receive arrays often cannot satisfy the requirements in B1 and bandwidth for ultra-high field spectroscopic imaging. We have developed and constructed a tight fit 400MHz 8-channel transceiver array. The array improved transmit efficiency and homogeneity in the axial slab through the phantom’s center when used in CP mode. B1+ averaged over the central axial slice measured 55.6 nT/V, which corresponds to 12.4 uT per 1 kW of RF power delivered directly to the array.

14:42 0623.   
Fast Electromagnetic Analysis of Transmit RF Coils based on Accelerated Integral Equation Methods
Jorge Fernandez Villena1, Athanasios G. Polimeridis1, Bastien Guerin2, Yigitcan Eryaman1, Lawrence L. Wald2,3, Elfar Adalsteinsson1,3, Jacob K. White1, and Luca Daniel1
1Research Laboratory of Electronics, Dept. of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 2A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 3Harvard-MIT Division of Health Sciences Technology, Cambridge, MA, United States

We propose a methodology for the comprehensive full-wave electromagnetic analysis of arbitrary MRI transmit coils within few minutes for a given realistic body model at a given frequency. It allows us to compute the un-tuned coil port parameters, to obtain the current distribution for the tuned coils, and the corresponding electromagnetic field distribution in the inhomogeneous body for each transmit channel. Such an approach is fast enough (2-3 minutes for 8-coil arrays) to be applied in automatic procedures for the optimization of high field coil designs based on the electromagnetic field distribution in realistic inhomogeneous human body models.

14:54 0624.   Bilateral Breast Imaging using Split-Symmetric Parallel Transmission
Ryan Brown1, Martijn A Cloos1, Christian Geppert2, Linda Moy1, Daniel K Sodickson1, and Graham C Wiggins1
1The Bernard and Irene Schwartz Center for Biomedical Imaging, Dept. of Radiology, New York University School of Medicine, New York, NY, United States, 2Siemens Medical Solutions USA Inc., New York, NY, United States

High-field bilateral breast imaging is challenging because of the conflicting requirements of a uniform transmit field and a large field-of-view. This is addressed in the proposed split-symmetric transmission scheme, where symmetries in the body anatomy and coil array are exploited to allow a given RF shim or set of tailored pulses to be replicated across lateral and contralateral coils. This allowed a substantial advantage in the degrees of freedom associated with the transmit optimization problem, and resulted in a uniform excitation over a bilateral field-of-view. Important benefits of this transmit system are that tailored parallel pulses and dedicated lymph node coils provide improved coverage in the posterior breast and in the lymph nodes, both of which have been difficult to visualize at 7T with standard transmit coils.

Madhwesha Rama Rao1, Fraser Robb2, and Jim M Wild1
1Academic Unit of Radiology, University of Sheffield, Sheffield, South Yorkshire, United Kingdom, 2GEHC Coils, General Electric Company, Aurora, Ohio, United States

Synchronous acquisition of 1H and HP gases in the lungs provide complementary structure function information from the lung with inherent spatial temporal registration. To date 1H images have been acquired using the systems body coil, which has low SNR compared to dedicate receive coils. This study demonstrates the design and application of a dedicated 1H receiver array to improve the proton lung SNR in synchronous acquisition with HP gas 3He and 129Xe at 1.5T. Synchronous acquisition with two birdcage transmitter receiver arrays has also been demonstrated. Both represent novel developments in the field of multi nuclear MRI RF engineering

15:18 0626.   Development and evaluation of a solid endorectal coil for 7 Tesla
Gregory J. Metzger1, Iris Elliott2, Jinfeng Tian1, Devashish Shrivastava1, Pierre-Francois van de Moortele1, and Gregor Adriany1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, 2Hologic, Toronto, Ontario, Canada

A reusable, multi-channel ERC with improved receive performance has been constructed and validated for use in both anatomic and demanding functional studies of the prostate at 7T. The availability of a sterilizable coil will make the use of an ERC a viable option for future clinical trials at UHF.