Yigitcan Eryaman¹, Patrick Zhang¹, Lynn Utecht¹, Russell L Lagore¹, Jeramy Kulesa¹, Lance DelaBarre¹, Kivanc Kose², Lynn E. Eberly³, Gregor Adriany¹, Kamil Ugurbil¹, and J. Thomas Vaughan^1
1CMRR,Radiology, University of Minnesota, Minneapolis, MN, United States, ²Dermatology Service, Memorial Sloan Kettering Cancer Center, New York, NY, United States, ³Division of Biostatistics,School of Public Health, University of Minnesota, Minneapolis, MN, United States

Preliminary studies are conducted to investigate the effects of 10.5 T whole body exposure on anesthetized pigs. Blood pressure was measured invasively, recorded and analyzed to calculate the systolic/diastolic blood pressure levels as well as the heart rate. 

Donald McRobbie^1,2
1South Australian Medical Imaging, Flinders Medical Centre, Adelaide, Australia, ²Surgery, Imperial College, London, United Kingdom

The Spatial Extended Non-linear Node (SENN) model currently used in MR safety guidelines does not adequately predict the behaviour of magnetic stimulation in terms of its time constant and waveform dependence. This has implications for the setting of gradient limits in MRI. Stimulation of the nerve by induced electric fields perpendicular to the nerve axis may remove the inconsistencies. A better model of magnetic stimulation is required.

Neerav Dixit¹, Pascal Stang², John Pauly¹, and Greig Scott^1
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Procyon Engineering, San Jose, CA, United States

Thermo-acoustic ultrasound uses pressure waves generated by thermoelastic expansion to measure heating. This technique can be used to detect excessive local SAR and RF tip heating in implanted or interventional devices. We compare the signal quality and inherent properties of several modulation schemes for thermo-acoustic ultrasound. We then interface a system for thermo-acoustic detection of heating with an MRI scanner and demonstrate the first use of thermo-acoustic ultrasound to detect RF tip heating from an MRI scanner.

Mihir Rajendra Pendse¹, Riccardo Stara^1,2,3, Gianluigi Tiberi⁴, Alessandra Retico², Michela Tosetti⁵, and Brian Rutt^1
1Stanford University, Stanford, CA, United States, ²Istituto Nazionale di Fisica Nucleare (Pisa), Pisa, Italy, ³Universita' di Pisa, Pisa, Italy, ⁴IMAGO7, Pisa, Italy, ⁵ISRCC Stella maris, Calambrone (Pisa), Italy

The use of a Butler matrix in pTx is thought to allow transmit channel compression by a factor of 2 or more compared to direct drive, while maintaining similar flip angle control. However, the SAR-related consequences of this compression strategy are relatively unexplored. Using a SAR-aware pTx design method (IMPULSE), we demonstrate that excellent flip angle uniformity is indeed possible using only 2 or 4 Butler modes compared to 8 direct drive channels; however, this comes at the expense of increased SAR. We also present a generalized strategy for selecting the optimal subset of Butler modes, i.e. the subset that provides adequate flip angle control at minimum SAR. 

Bastien Guerin^1,2, Jorge F. Villena³, Athanasios G. Polimeridis⁴, Elfar Adalsteinsson^5,6,7, Luca Daniel⁵, Jacob K. White⁵, Bruce R. Rosen^1,2,6, and Lawrence L. Wald^1,2,6
1A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Cadence Design Systems, Feldkirchen, Germany, ⁴Skolkovo Institute of Science and Technology, Moscow, Russian Federation, ⁵Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ⁶Harvard-MIT Division of Health Sciences Technology, Cambridge, MA, United States, ⁷Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, United States

We propose a framework for the computation of the ultimate hyperthermia, which is the best possible hyperthermia treatment for a given frequency and non-uniform body model achievable by any multi-channel hyperthermia coil. We compute the ultimate hyperthermia treatment of two shallow (close to skull) and deep (close to ventricle) brain tumors in the realistic “Duke” body model and for treatment frequencies ranging from 64 MHz to 600 MHz. We characterize the convergence to the ultimate SAR pattern as well as temperature increase associated with the ultimate SAR distribution in the presence of non-uniform perfusion effects.

Stephan Orzada¹, Mark E. Ladd^1,2, and Andreas K. Bitz^2
1Erwin L. Hahn Institute, Essen, Germany, ²Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

The capability of multi-channel transmit systems to drive different waveforms in the individual transmit channels results in an increased complexity for the SAR supervision In this work we propose a method based on virtual observation points (VOPs) to derive a conservative upper bound for the local SAR with a reasonable safety margin without knowledge of the transmit phases of the channels. In six different scenarios we demonstrate that the proposed method can be superior to the simple worst case method often used when only amplitude and no phase information is available.

Leeor Alon^1,2,3,4, Daniel Sodickson^1,2,3, and Cem M. Deniz^1,2,3,4
1Center for Advanced Imaging Innovation and Research (CAI2R), New York University School of Medicine, New York, NY, United States, ²Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, ³NYU Wireless, NYU-Poly, New York, NY, United States, ⁴RF Test Labs, New York, NY, United States

MR thermometry methods are often used to assess safety of RF antennas. Typically thermal mapping is conducted in phantoms, which measures the temperature change as result of exposure to RF waves. From these temperature difference maps, SAR distribution can be reconstructed using the inverse heat equation (HEI) framework . With a goal of of testing the robustness of this method, in this work, we assessed the fidelity of the algorithm with respect to different regularization parameter, different SAR distributions, excitation frequencies and heating durations.

Laleh Golestanirad¹, Boris Keil¹, Maria Ida Iacono², Giorgio Bonmassar¹, Leonardo M Angelone², Cristen LaPierre¹, and Lawrence L Wald^1
1Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ²Division of Biomedical Physics, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, US Food and Drug Administration, Silver Spring, MD, United States

Recently we presented the feasibility study of using a reconfigurable DBS-friendly head coil, composed of a patient-adjustable rotating birdcage transmitter, and an integrated 32-channel receiver array to reduce SAR during imaging of patients with deep brain stimulation implants. Here we introduce the first prototype of such coil system, and present results of finite element simulations on patient-derived numerical models of realistic DBS lead trajectories, which characterize its SAR reduction performance.

Wan Luo^1,2, Shao Ying Huang¹, Jiasheng Su¹, Zu-Hui Ma¹, and J. Thomas Vaughan^3
1Singapore University of Technology and Design, Singapore, Singapore, ²University of Electronic Science and Technology of China, Chengdu, China, People's Republic of, ³University of Minnesota, Minneapolis, MN, United States

When B₀ in a MRI system increases, peaks and nulls are formed in the energy/field distribution inside the subject under scan, which causes safety issues and deteriorates imaging accuracy, respectively. Therefore, a quick and accurate electromagnetic simulation of the human body is crucial for predicting the temperature and specific absorption rate distribution before a scan. Here, we develop a solver based on the weak-form volume integral equation (VIE) and accelerated by the fast Fourier transform method. It requires much less CPU time and memory compared with the traditional strong-form VIE and the popular FDTD-based commercial software SEMCAD.

Elena Lucano^1,2, Mikhail Kozlov³, Eugenia Cabot⁴, Sara Louie⁵, Marc Horner⁵, Wolfgang Kainz¹, Gonzalo G Mendoza¹, Aiping Yao^4,6, Earl Zastrow^4,6, Niels Kuster^4,6, and Leonardo M Angelone^1
1Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, MD, United States, ²Department of Information Engineering, Electronics and Telecommunications, University of Rome "Sapienza", Rome, Italy, ³MR:comp GmbH, Gelsenkirchen, Germany, ⁴IT'IS foundation, Zurich, Switzerland, ⁵ANSYS, Inc., Canonsburg, PA, United States,⁶Department of Information Technology and Electrical Engineering, ETH, Zurich, Switzerland

Preliminary results of an ongoing inter-laboratory study are presented. The eventual purpose of the effort is to develop a methodology that harmonizes RF-modeling and RF-testing protocol for use in RF exposure assessment. In this phase of the study, numerical and experimental data were collected from four laboratories for unloaded and loaded coil conditions. Only information about the geometry and resonance frequency of the physical coil was provided. Qualitatively good agreement across all teams was found. Subsequent phases of the study shall include a methodology on uncertainty analysis associated with the numerical and experimental methods that can be used in practice