ISMRM 24th Annual Meeting & Exhibition 07-13 May 2016 Singapore

Scientific Session: Dipoles & Dielectrics

Tuesday, May 10, 2016
Room 324-326
13:30 - 15:30
Moderators: Riccardo Lattanzi, Thoralf Niendorf

Numerical evaluation of the optimal coupling scheme of a cylindrical dielectric resonator operating at 600 MHz (14T)
Wei Luo1, Rui Liu2, Thomas Neuberger3,4, and Michael T Lanagan1,2
1Material Research Institute, University Park, PA, United States, 2Department of Engineering Science and Mechanics, University Park, PA, United States, 3Huck Institute of Life Science, University Park, PA, United States, 4Department of Biomedical Engineering, University Park, PA, United States
To maximize the energy transfer to the cylindrical dielectric resonator utilized in magnetic resonant imaging probe head, a three-loop coupling method was investigated using electromagnetic field simulations. The simulation results demonstrate the supreme performance of this coupling method and verify the previous preliminary experimental results.

More than meets the eye: The mixed character of electric dipole coils, and implications for high-field performance
Daniel K Sodickson1,2, Graham C Wiggins1,2, Gang Chen1,2, Karthik Lakshmanan1, and Riccardo Lattanzi1,2
1Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States
We present a fundamental electrodynamic explanation for the SNR performance of electric dipole antennae at high field.  We demonstrate that typical electric dipole coils combine divergence-free and curl-free surface current components, allowing them to exceed the performance limits for either component alone.  We also show that z-directed electric dipoles have a strong overlap with ideal current patterns associated with the ultimate intrinsic SNR at high field strength.

Towards imaging the body at 10.5 Tesla using a fractionated dipole antenna array
M. Arcan Erturk1, Gregor Adriany1, Pierre-Francois Van de Moortele1, Yigitcan Eryaman1, Alexander J Raaijmakers2, Lance DelaBarre1, Edward Auerbach1, J. Thomas Vaughan1, Kamil Ugurbil1, and Gregory J Metzger1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, 2Imaging Division, UMC Utrecht, Utrecht, Netherlands
We have developed a fractionated dipole antenna (fDA) for body imaging at 10.5T, investigated its electro-magnetic field behavior in a 10-channel array using numerical simulations in a human model, and compared its performance to a 10-channel fDA array at 7.0T. The 10.5T fDA array provided similar B1+ transmit efficiency and peak 10g-averaged SAR compared to the 7.0T array inside the prostate, however had a less uniform B1+ distribution. Simulation results indicated that fDA elements have sufficient B1+ penetration at 10.5T, but B1+ non-uniformities may need to be alleviated even in small imaging targets using dynamic RF strategies including parallel transmit.

Disentangling Signal propagation and Noise-related Effects in the Presence of High Permittivity Materials via Ideal Current Patterns
Manushka V. Vaidya1,2,3, Christopher M. Collins1,2,3, Daniel K. Sodickson1,2,3, Giuseppe Carluccio1,2, and Riccardo Lattanzi1,2,3
1Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, NY, United States, 2Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 3Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States
There is no single mechanism to describe how high permittivity materials (HPMs) improve signal-to-noise ratio when placed between radiofrequency coils and the object. We separately investigated the effects of HPMs on signal propagation and sample noise by studying ideal current patterns, the corresponding optimal electric (E) field and a signal-only propagation model. Our results suggest that phase changes in the ideal current patterns with HPMs are primarily due to signal-propagation effects while their increase in size is due to reduced E field penetration into the sample, which allows larger current patterns that maximize signal reception with a limited noise penalty.

Combined loop-dipole transceiver array for body imaging at 7.0 Tesla
M. Arcan Erturk1, Alexander J Raaijmakers2, Gregor Adriany1, Kamil Ugurbil1, and Gregory J Metzger1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, 2Imaging Division, UMC Utrecht, Utrecht, Netherlands
We developed a 16-channel transceiver body array (16LD) by combining loop and dipole elements, and compared performance against 16-channel microstrip-line (16ML) and 10-channel fractionated dipole antenna (10DA) arrays. Complementary field characteristics of loop and dipole elements were utilized by symmetrically placing them along their long-axes. The loop-dipole combination allowed increased channel counts and density while limiting inter-element coupling. The 16LD had improved transmit and receive performance over the 16ML and 10DA in both simulations and experiments. Images of the prostate, kidneys and heart were acquired showing the potential of the 16LD to successfully image targets throughout the body at 7.0T.

Modular 7 Tesla transmit/receive arrays designed using thin very high permittivity dielectric resonator antennas
Thomas O'Reilly1, Thomas Ruytenberg1, Bart Steensma2, Alexander Raaijmakers2, and Andrew Webb1
1Leiden University Medical Centre, Leiden, Netherlands, 2Utrecht Medical Centre, Utrecth, Netherlands
A transmit/receive dielectric resonator antenna array has been designed for operation at 7 Tesla. By using very thin high permittivity material the inter-element coupling is very low, allowing small resonators to be placed very close to one another. An eight-element array has been simulated and constructed, and in vivo images of the extremities acquired.

Practical improvements in the design of high permittivity pads for dielectric shimming in 7T neuroimaging
Thomas O'Reilly1, Wyger Brink1, and Andrew Webb1
1Leiden University Medical Centre, Leiden, Netherlands
Improvements are proposed for practical use of high permittivity materials in high field neuroimaging. These result in a simple formula to design materials with specified permittivity, formulation to improve the short term rigidity and long term stability of the material, and a method to incorporate devices such as headphones into the dielectric pad design.

Body imaging at 7 Tesla with much lower SAR levels: an introduction of the Snake Antenna array
Bart Steensma1, Alexa Viviana Obando Andrade2, Dennis Klomp1, Nico van den Berg1, Peter Luijten1, and Alexander Raaijmakers1
1University Medical Centre Utrecht, Utrecht, Netherlands, 2TU Delft, Utrecht, Netherlands
The snake antenna is introduced as a novel transmit array element for body-imaging at ultrahigh-field strengths.  It has been shown in simulations that the snake antenna causes a very low local peak SAR compared to the fractionated dipole antenna, while maintaining sufficient B1+-signal strength. In vivo prostate scans show that the snake antenna array reaches a B1+-signal strength in the prostate that is slightly higher than the signal strength reached by the fractionated dipole antenna array. The lower SAR of the snake antenna considerably relaxes scanning constraints for body imaging.

Prospect of SNR and SAR Improvement on a Whole-body Human 10.5T Scanner using High Dielectric Material
Sebastian Rupprecht1, Hannes M Wiesner2, Pierre-Francois van De-Mortelle2, Byeong-Yeul Lee2, Wei Luo3, Xiao-Hong Zhu2, Isaiah Duck1, Gregor Adriany2, Christopher Sica1, Kamil Ugurbil2, Michael Lanagan3, Wei Chen2, and Qing Yang1
1Department of Radiology, The Pennsylvania State University College of Medicine, Hershey, PA, United States, 2Radiology Department, Center for Magnetic Resonance Research, Minneapolis, MN, United States,3Department of Engineering Sciences and Mechanics, The Pennsylvania State University, State College, PA, United States
We compared and characterized the RF field wave behavior for human brain imaging at 10.5T and 7T. Additionally we explored the feasibility of using monolithic high dielectric constant materials to potentially further enhance SNR and circumvent SAR limitations and show that there can be great benefits through phantom experiments and computer modeling.

Optimized ICE-decoupled Monopole Array for Human Head Imaging at 7T
Xinqiang Yan1 and Xiaoliang Zhang2
1Key Laboratory of Nuclear Analysis Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China, People's Republic of, 2Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States
Induced current elimination (ICE) method has proved to be a useful approach in decoupling radiative monopole and dipole arrays. In this study, we aim to investigate the effect of ICE decoupling elements and their position to the B1 fields. The MR imaging and simulation results show that an optimized arrangement of ICE decoupling elements can be found to minimize the perturbation of decoupling elements. Compared with the non-optimized ICE decoupled monopole array, the optimized array has more homogeneous transmit field and has no dark spots or signal cancellations in the MR images.

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