Wei Luo¹, Rui Liu², Thomas Neuberger^3,4, and Michael T Lanagan^1,2
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.

Daniel K Sodickson^1,2, Graham C Wiggins^1,2, Gang Chen^1,2, Karthik Lakshmanan¹, and Riccardo Lattanzi^1,2
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.

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 Metzger^1
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.

Manushka V. Vaidya^1,2,3, Christopher M. Collins^1,2,3, Daniel K. Sodickson^1,2,3, Giuseppe Carluccio^1,2, and Riccardo Lattanzi^1,2,3
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.

M. Arcan Erturk¹, Alexander J Raaijmakers², Gregor Adriany¹, Kamil Ugurbil¹, and Gregory J Metzger^1
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.

Thomas O'Reilly¹, Thomas Ruytenberg¹, Bart Steensma², Alexander Raaijmakers², and Andrew Webb^1
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.

Thomas O'Reilly¹, Wyger Brink¹, and Andrew Webb^1
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.

Bart Steensma¹, Alexa Viviana Obando Andrade², Dennis Klomp¹, Nico van den Berg¹, Peter Luijten¹, and Alexander Raaijmakers^1
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.

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 Yang^1
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.

Xinqiang Yan¹ and Xiaoliang Zhang^2
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.