Marco Müller¹, Reiner Umathum¹, Werner Wiesbeck², and Michael Bock^3
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.

Daniel Brenner¹, Frank Geschewski¹, Jörg Felder¹, Kaveh Vahedipour¹, Tony Stöcker¹, and N. Jon Shah^1,2
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.

Yujuan Zhao¹, Daniel K. Stough¹, Hai Zheng¹, Tiejun Zhao², Chad T. Harris³, William B. Handler³, Blaine A. Chronik³, Fernando E. Boada¹, and Tamer S. Ibrahim^1
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.

Jose Antonio Muniz^1,2, Alexey A Tonyushkin^3,4, Andrew J M Kiruluta^3,4, and Samuel Colles Grant^1,2
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.

Sebastian Arnold Aussenhofer¹, Josef Hubensteiner¹, and Andrew G Webb^1
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.

Hugo Kroeze¹, Irene M.L. van Kalleveen¹, Marielle E.P. Philippens², Onne Reerink², Peter R Luijten¹, and Dennis W.J. Klomp^1
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.

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 Berg^1
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.

Graham Charles Wiggins¹, Bei Zhang¹, Riccardo Lattanzi¹, Gang Chen², and Daniel Sodickson^1
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.

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. Klomp^1
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.

Lukas Winter¹, Celal Özerdem¹, Werner Hoffmann², Helmar Waiczies¹, Davide Santoro¹, Alexander Müller¹, Tomasz Lindel¹, Wolfgang Renz^1,3, Conrad Martin¹, Frank Seifert², Bernd Ittermann², and Thoralf Niendorf^1,4
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