Novel RF Coil Concepts

Tuesday 13 May 2014

Karthik Lakshmanan¹, Martijn Cloos¹, Ricardo Lattanzi¹, Daniel Sodickson¹, and Graham Wiggins^1
1Department of Radiology, The Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, NewYork, NewYork, United States

A novel single antenna element which can capture both magnetic and electric dipole fields and achieve an improved performance compared to conventional surface coil loops at ultra high field.

Walker J. Turner¹, Garrett W. Astary², Barbara L. Beck³, Thomas H. Mareci², and Rizwan Bashirullah^1
1Electrical and Computer Engineering, University of Florida, Gainesville, FL, United States, ²Biochemistry and Molecular Biology, University of Florida, Gainesville, FL, United States, ³Advanced Magnetic Resonance Imaging and Spectroscopy Facility, McKnight Brain Institute, University of Florida, Gainesville, FL, United States

We propose an implantable device capable of increasing the signal sensitivity of nuclear magnetic resonance (NMR) measurements at multiple frequencies and field strengths for use in monitoring bio-artificial organs post-implantation. The device enables complete wireless control of the resonance of a single-turn detection coil, coupled to the already existing NMR excitation/acquisition coil, across a wide range of frequencies associated with important metabolic nuclei in both 4.7Tesla and 11.1Tesla magnetic field strengths. Device functionality was validated through NMR experiments on tissue equivalent gel phantoms resulting in ~2x increase in NMR signal sensitivity.

Jens Hoffmann^1,2, Christian Mirkes^1,3, G. Shajan¹, Klaus Scheffler^1,3, and Rolf Pohmann^1
1High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tuebingen, BW, Germany, ²Graduate School of Neural & Behavioural Sciences, Tuebingen, BW, Germany, ³Department for Biomedical Magnetic Resonance, University of Tuebingen, Tuebingen, BW, Germany

Three waveguide modes propagate in a 9.4 T whole-body scanner compared to only two modes at 7 T. While three modes are still insufficient to homogenize the B1 field across larger volumes, a time-interleaved acquisition of two complementary RF shims (TIAMO) and the subsequent sum-of-squares reconstruction of the single images is suitable to achieve whole-brain coverage without signal dropouts. Using simulations, we show that excitation inhomogeneity (max-to-min ratio) can be reduced by a factor of 2 (4) compared to CP mode. Finally, void-free whole-brain traveling-wave MRI at 9.4 T is demonstrated in vivo using a compact, adjustable 3-port antenna.

Jason P Stockmann¹, Thomas Witzel¹, Boris Keil¹, Azma Mareyam¹, Jon Polimeni¹, Cris LaPierre¹, and Lawrence L Wald^1,2
1Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States,²Harvard Medical School, Boston, MA, United States

We demonstrate a 32ch integrated RF/multi-coil (MC) shim array that combines both functions in the same array of single-turn loops. Placing large arrays of loops as close as possible to the body maximizes the efficiency of both RF reception and B0 shimming. The array shows SNR comparable to a commercial 32ch coil while generating the needed B0 variation in the body for high-performance shimming with less than 3 amps per loop. Off-line shimming of 3T brain inhomogeneity using acquired shim array field maps mitigates the sinus B0 hot spot and reduces the 20-slice standard deviation from 74.2 to 44.6 Hz.

Myung-Kyun Woo¹, Suk-Min Hong¹, Young-Bo Kim¹, and Zang-Hee Cho^1
1Neuroscience Research Institute, Gachon University, Incheon, Korea

The purpose of the present study was to investigate whether a modified monopole antenna with both extension and individual shields would provide not only improved coverage of the brain but also uniformity on all planes at 7T. We constructed an 8-channel MA, EMA and EMAIS and compared their transmit properties, SNR and receiver sensitivity.

Gang Chen¹, Martijn Cloos¹, Riccardo Lattanzi¹, Daniel Sodickson¹, and Graham Wiggins^1
1The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States

Investigations of the Ultimate Intrinsic SNR (UISNR) have revealed that curl-free current modes make a significant, even dominant, contribution to central UISNR at high frequencies and for large objects. For a body-sized phantom at 7T, the ideal current pattern for curl-free current modes shows V-shaped patterns, which provide the phase evolution in the axial direction needed to account for propagation delays to the central region of interest. We show in simulations that bending an electric dipole into a V can better approximate the ideal current phase evolution and provide superior performance compared to a straight dipole.

Sebastian Rupprecht¹, Byeong-Yeul Lee², Xiao-Hong Zhu², Wei Chen², and Qing X Yang^1,3
1Center for NMR Research, Penn State College of Medicine, Department of Radiology, Hershey, PA, United States, ²Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, United States, ³Center for NMR Research, Penn State College of Medicine, Department of Neurosurgery, Hershey, PA, United States

Previously ultra-high dielectric constant (uHDC) materials have shown to greatly improve proton MR imaging at 3 T. In this study we are trying to explore the potential of utilizing such materials in a sleeve around the head to dramatically increase the signal-to-noise ratio by more than 100 %. At the same time we were able to cut the necessary transmit power for a standard single voxel spectroscopy in half while using the high dielectrics.

Christopher M. Collins¹, Giuseppe Carluccio¹, Manushka V. Vaidya¹, Gillian G. Haemer¹, Wei Luo², Riccardo Lattanzi¹, Graham C. Wiggins¹, Daniel K. Sodickson¹, and Qing X. Yang^3
1Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, ²Bioengineering, The Pennsylvania State University, PA, United States, ³Radiology, The Pennsylvania State University, PA, United States

While most work with high permittivity materials (HPMs) in MRI has been focused on improving SNR or transmit efficiency for a relatively small region within a much larger coil or array, our recent work demonstrates that HPMs can also improve performance of small coils very near the subject, as well as arrays of such coils for the entire region of the anatomy they encompass. Here we introduce theoretical arguments for how this can occur before presenting numerical demonstrations that HPMs will, indeed, increase SNR and reduce SAR within the entire cerebrum for a specific close-fitting head-specific HPM/array combination at 7T.

Christopher Sica¹, Wei Luo², Sebastian Rupprecht¹, Michael Lanagan², Christopher Collins³, Raffi Sahul⁴, Seongtae Kwon⁴, and Qing Yang^1
1Radiology, Penn State College of Medicine, Hershey, Pennsylvania, United States, ²Engineering Science and Mechanics, Penn State University, Pennsylvania, United States, ³Radiology, New York University, New York, New York, United States, ⁴TRS Technologies, State College, Pennsylvania, United States

A novel configuration incorporating high dielectric material (εr ~1200) was evaluated experimentally at 3T in the human brain and numerically with FDTD simulation for SAR reduction, B1+ enhancement and SNR improvement. The 10g average whole body SAR and whole brain SAR was reduced by 80.3% and 59.8%. System transmit power in experiment is reduced by 70%. The measured B1+ coefficient of variation was reduced on average by 30% across 16 slices in the brain. SNR gains of 40-50% in the periphery of the brain were observed.

Manushka V. Vaidya¹, Daniel K. Sodickson¹, Christopher M. Collins¹, and Riccardo Lattanzi^1
1Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States

High-permittivity material (HPM) can be used to shape and/or enhance the magnetic field associated with a radiofrequency (RF) coil. We showed in simulations that placing discs of HPM beneath and beside an RF coil can extend its sensitivity, improving transmit efficiency and SNR as compared to a single surface coil covering the same field of view. The results are comparable to the case of a surface array of three loops with the same total dimensions. Our results suggest that HPMs could be used to improve coil performance when the number of transmit or receive channels is limited.