Emerging RF Coils & Technologies
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Thursday 10 May 2012
Room 202  10:30 - 12:30 Moderators: Daniel K. Sodickson, J. Thomas Vaughan

10:30 0534.   
8 channel travelling wave coil array
Marco Müller1, Reiner Umathum1, Werner Wiesbeck2, and Michael Bock3
1Dept. of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, 2Dept. of Radiofrequency and Electronics, Karlsruhe Institute of Technology (KIT), 3Dept. of Radiology, Medical Physics, University Hospital Freiburg, Freiburg

The classical travelling wave patch antenna concept leads to high global SAR and to RF wave reflection at head, shoulders or at the lower extremities. We introduce a multifrequency 8-channel travelling wave RF array to solve these problems by confining the SAR to the imaging area. For evaluation RF nearfield robotic measurements at 300 MHz were performed and compared to accordant FDTD simu¬la¬tions. At 7 Tesla B1 maps were performed and a human leg was imaged. As a future prospect the usability of this concept for whole body imaging was investigated by FDTD simu¬la¬tions with a detailed anatomical model.

10:42 0535.   B1 Shimming with a Multi-Mode Travelling Wave Antenna at 9.4T
Daniel Brenner1, Frank Geschewski1, Jörg Felder1, Kaveh Vahedipour1, Tony Stöcker1, and N. Jon Shah1,2
1Institute of Neuroscience and Medicine - 4, Forschungszentrum Jülich, Jülich, Germany, 2JARA - Faculty of Medicine, RWTH Aachen University, Aachen, Germany

Travelling waves have been introduced as an alternative excitation technique for UHF MRI. Recently, the extension to multi-channel excitation was presented at 7T using dielectric fillings of the magnet bore. At 9.4T (~400MHz), to excite multiple modes without the necessity of such a dielectric filing becomes feasible. Building on initial performance measurements of the multi-mode antenna this work shows the prospects of RF shimming with the multi-mode antenna. The RF shimming is capable of reducing localised RF inhomogeneities in a phantom experiment. Though it cannot completely overcome the problem of B1 dropouts.

10:54 0536.   Maximizing RF efficiency and minimizing eddy current artifacts using RF and eddy current simulations
Yujuan Zhao1, Daniel K. Stough1, Hai Zheng1, Tiejun Zhao2, Chad T. Harris3, William B. Handler3, Blaine A. Chronik3, Fernando E. Boada1, and Tamer S. Ibrahim1
1University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2Siemens Medical Solutions, Pittsburgh, PA, United States, 3University of Western Ontario, London, Ontario, Canada

Synopsis: In this work, we present a new and an elaborate dual-optimization method that maintains RF-coil RF characteristics and simultaneously reduces low frequency magnetic field distortions due to eddy currents. The optimization is guided by full wave electromagnetic simulation combined with eddy current simulation. The designs were successfully tested on a 7T human scanner using phantoms and 4 in-vivo subjects.

11:06 0537.   Working with Nulls, Reflections and Artifacts: Modified EM Mode Propagation in a Dielectric Waveguide at 21.1 T
Jose Antonio Muniz1,2, Alexey A Tonyushkin3,4, Andrew J M Kiruluta3,4, and Samuel Colles Grant1,2
1Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL, United States, 2Chemical & Biomedical Engineering, The Florida State University, Tallahassee, FL, United States, 3Radiology, Massachusetts General Hospital, Boston, MA, United States,4Physics, Harvard University, Cambridge, MA, United States

Traveling wave MRI can be optimized by altering the dimensions and materials applied in waveguide construction. For a widebore magnet operating at 21.1 T (1H Larmor of 900 MHz), far field imaging and traveling waves cannot occur in an empty, bore-sized waveguide; however, the introduction of a concentric dielectric within the waveguide does support wave propagation. As such, there exists the opportunity to evaluate the dielectric as a means to alter electromagnetic modes. This study investigates optimization of ultra-high field traveling wave MRI at 21.1 T by varying the diameter, permittivity and geometric layout of dielectrics within a cylindrical waveguide.

11:18 0538.   
A quadrature HEM11 mode resonator as a new volume coil for high field MRI
Sebastian Arnold Aussenhofer1, Josef Hubensteiner1, and Andrew G Webb1
1Department of Radiology, Leiden University Medical Center, C.J.Gorter Center for High Field MRI, Leiden, Zuid-Holland, Netherlands

A cavity resonator based on water as a dielectric is simulated, designed and tested to excite the degenerate quadrature HEM11 modes for a human 7T magnet. Results of the electromagnetic simulation show good RF homogeneity for an annular resonator with different parts of the body inside the annulus. Images of the wrist of a healthy human volunteer were acquired, showing the promise of this new type of high field volume resonator.

11:30 0539.   First results experimental thin rectal probe for high field MRI
Hugo Kroeze1, Irene M.L. van Kalleveen1, Marielle E.P. Philippens2, Onne Reerink2, Peter R Luijten1, and Dennis W.J. Klomp1
1Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands, 2Radiotherapy, UMC Utrecht, Utrecht, Utrecht, Netherlands

An experimental thin rectal probe was developed for high field MRI. At 300 MHz short electrical dipoles and monopoles can be used instead of conventional coils, making the antenna very thin. This allows insertion of the antenna in narrow lumina. Simulations showed that with an RF power of 25 W a B1+ of 10 uT could be obtained at a distance of 20 mm from the antenna. This was confirmed in a phantom experiment. High resolution FFE images were obtained with this antenna rectally inserted in a healthy, male volunteer.

11:42 0540.   
Torus-shaped dielectric resonator for 7T musculoskeletal imaging
Johanna J. Bluemink1, Wouter Koning2, Dennis W. Klomp2, Hugo Kroeze2, Stefan Maderwald3, Anke Henning4, Peter R. Luijten2, Jan J.W. Lagendijk1, and Cornelis A.T. van den Berg1
1Radiotherapy, University Medical Center Utrecht, Utrecht, Netherlands, 2Radiology, University Medical Center Utrecht, Utrecht, Netherlands, 3Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany, 4ETH Zürich, Switzerland

A torus-shaped dielectric resonator is introduced and a proof of concept is given for imaging at 7T. Due to the relatively high frequency of 300 MHz, water can be used as a dielectric while the torus has practical dimensions. Experimental B1+ patterns show good comparison to those obtained in numerical simulations. In-vivo images of the human calf at 7T are obtained using the torus as a transmit/receive coil.

11:54 0541.   The Electric Dipole Array: An Attempt to Match the Ideal Current Pattern for Central SNR at 7 Tesla
Graham Charles Wiggins1, Bei Zhang1, Riccardo Lattanzi1, Gang Chen2, and Daniel Sodickson1
1The Bernard and Irene Schwartz Center for Biomedical Imaging, NYU Medical Center, New York, NY, United States, 2The Sackler Institute of Graduate Biomedical Science, NYU School of Medicine, New York, NY, United States

Analysis of the Ultimate Intrinsic SNR (UISNR) makes it possible to plot the current pattern on a given surface which corresponds to the UISNR for a given position within the phantom. For cylindrical geometries and optimizing for the center of the phantom, the current patterns can appear like distributed electric dipoles at high field, with current flowing in straight lines along the length of the cylinder with no return path. To mimic this pattern an array of 8 dipole antennas has been constructed for 7T and compared to conventional coil designs.

12:06 0542.   
RF shimming of the neck using a 2 and a 4 channel travelling wave neck array at 7T MRI
Wouter Koning1, Johanneke H. Bluemink1, Vincent O. Boer1, Alexander Raaijmakers1, Anke Henning2, Jaco J.M. Zwanenburg1, Cornelis A.T. van den Berg1, Peter R. Luijten1, and Dennis J.W. Klomp1
1University Medical Center, Utrecht, Netherlands, 2ETH, Zurich, Switzerland

For neck imaging with 7T MRI the versatility of 2 and a 4 channel transmit array was evaluated. The array consists of a neck pillow filled with D2O. The pillow acts as a leaky waveguide in which a wave is fed by 2 or 4 radiative antenna’s. RF shimming is used to demonstrate versatility: focussing the RF with the 2 channel system allows imaging of carotids and spine. Going from 2 to 4 channels allows for homogeneity improvement and reduction of SAR.

12:18 0543.   
Design and Evaluation of an Eight Channel TX/RX Hybrid Applicator for Imaging and Targeted RF-Heating at 7.0 T
Lukas Winter1, Celal Özerdem1, Werner Hoffmann2, Helmar Waiczies1, Davide Santoro1, Alexander Müller1, Tomasz Lindel1, Wolfgang Renz1,3, Conrad Martin1, Frank Seifert2, Bernd Ittermann2, and Thoralf Niendorf1,4
1Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany, 2Physikalisch Technische Bundesanstalt (PTB), Berlin, Germany, 3Siemens Healthcare, Erlangen, Germany, 4Experimental and Clinical Research Center (ECRC), Charité - University Medicine Campus Berlin Buch, Berlin, Germany

Combining RF hyperthermia and MR imaging is conceptually appealing to pursue spatially and temporally controlled and monitored RF heating. The benefits of this approach could be used as an adjunctive therapy for established cancer treatments including radiotherapy and chemotherapy , targeted drug delivery and targeted MR contrast agent delivery. This study demonstrates the feasibility of an 8 channel TX/RX hybrid applicator tailored for imaging and targeted hyperthermia at 7.0T