Yiyi Ji¹, Lukas Winter², Lucila Navarro^3,4, Min-Chi Ku¹, João Periquito¹, Michal Pham¹, Werner Hoffmann², Loryn E. Theune³, Marcelo Calderón^3,5,6, and Thoralf Niendorf^1,7
1Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin, Germany, ²Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany, ³Institute of Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany, ⁴Instituto de Desarrollo Tecnológico para la Industria Química (INTEC), Universidad Nacional del Litoral (UNL) - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Santa Fe, Argentina, ⁵POLYMAT and Applied Chemistry Department, Faculty of Chemistry, University of the Basque Country UPV/EHU, Donostia-San Sebastián, Spain, ⁶IKERBASQUE, Basque Foundation for Science, Bilbao, Spain, ⁷Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine, Berlin, Germany

Thermal Magnetic Resonance (ThermalMR) adds a thermal dimension to an MR device by exploiting the constructive interference of radiofrequency (RF) waves for temperature intervention. Here, the capacity of ThermalMR is demonstrated in a model system involving the release of a protein from thermoresponsive nanogels. Upon RF heating the nanogels (T=43°C), 29.3% of the protein were released after 6h which is in accordance with the release profile obtained for the reference data derived from a water bath setup. ThermalMR provides an ideal testbed for the study of temperature induced release of drugs, MR probes and other agents from thermoresponsive carriers.

Rasim Boyacioglu¹, Megan Poorman^2,3, Kathryn Keenan², and Mark Griswold^1
1Radiology, Case Western Reserve University, Cleveland, OH, United States, ²Physical Measurement Laboratory, National Institute of Standards and Technology, Boulder, CO, United States, ³Department of Physics, University of Colorado Boulder, Boulder, CO, United States

Conventional temperature monitoring is based on measurement of off-resonance via gradient-echo phase scans for non-adipose tissue. MRF with quadratic RF phase (MRFqRF) simultaneously quantifies off-resonance, T1, T2, and T2*. For a proof of principle thermometry experiment with MRFqRF, an ex-vivo aqueous sample was heated with laser ablation, temperature was tracked, and multiple continuous MRFqRF scans were obtained with different temporal resolutions. Scanner frequency drifts were removed automatically with Independent Component Analysis. Residual changes in off-resonance predict the temperature change. However, MRFqRF temporal resolution (~10s) needs to be increased further for clinical relevance.

Irene Kuang¹, Nick Arango¹, Jason Stockmann^2,3, Elfar Adalsteinsson^1,4, and Jacob White^1
1Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ²A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ³Harvard Medical School, Boston, MA, United States, ⁴Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, United States

Declining costs of permanent magnets and embedded systems electronics has driven systems engineering of point-of-care diagnostics to the forefront of MR research. We present a low-cost RF signal chain (<$100) for low-field imaging using a Teensy 4.0 microcontroller and STHV800 ultrasound pulser IC. Bloch-optimization simulation of programmable, dithered-pulses enables broadband excitation of the notably inhomogeneous permanent magnets employed in portable, hand-held MR systems.

Jason P. Stockmann^1,2, Lucia Navarro de Lara¹, Larry Wald^1,2, and Aapo Nummenmaa^1,2
1A. A. Martinos Center, Massachusetts General Hospital, Charlestown, MA, United States, ²Harvard Medical School, Boston, MA, United States

We explore the local field control capability of a 48ch TMS coil array to perform B0 shimming in the brain.  The array uses sixteen 3-axis TMS coils built using three independent orthogonal windings that provide added flexibility to orient the resultant magnetic dipole and thus facilitate tailoring the B0 shim field.  We propose adapting the TMS coils to carry DC shim currents during EPI fMRI time series acquisitions to reduce artifact levels and improve the utility of TMS-fMRI for studying brain circuits.

Christoph Michael Schildknecht¹, David Otto Brunner¹, and Klaas Paul Pruessmann^1
1ETH Zurich and University of Zurich, Zurich, Switzerland

Complex in-bore electronics (e.g. motion trackers, digitizer etc.) frequently requires various voltage rails. This poses especially a challenge when bi-polar voltages are required because in-bore voltage inversion is typically not possible due to the EMI of such converter. The here presented switched capacitator voltage inverter allows in-bore operation without disturbing the MRI scanner due to the very low EMI. Lab and 3T MRI measurement were performed to verify the EMC compatibility and characterize the device.

Sebastian Littin¹, Feng Jia¹, Philipp Amrein¹, Huijun Yu¹, Arthur Magill², Tristan Kuder², Mark E. Ladd², Frederik Laun³, Sebastian Bickelhaupt⁴, and Maxim Zaitsev^1
1Department of Radiology, Medical Physics, University of Freiburg, University Medical Center, Freiburg, Germany, ²Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany, ³Department of Radiology, MR Physics, University Medical Center Erlangen, Erlangen, Germany, ⁴Junior Group Medical Imaging and Radiology – Cancer Prevention, German Cancer Research Center (DKFZ), Heidelberg, Germany

The aim of this project is to design and implement a non-linear single channel breast gradient coil for diffusion encoding. Initial field maps of the prototype implementation are shown. The prototype should allow to generate gradient strengths between 1 and 3.6 [T/m].

Berk Silemek¹, Lukas Winter¹, Frank Seifert¹, Harald Pfeiffer¹, and Bernd Ittermann^1
1Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany

A Measurement-based Temperature-Matrix approach is presented that enables a fast, patient and exam specific estimation and mitigation of RF hazards of implants. Various locations in phantom are tested using an 8-channel (300MHz) implant safety testbed. Heating reduction Based on T-Matrix Measurements resulted >3 times heating reduction vs. circularly-polarized mode and >19 times vs. worst-case mode. 2-channel MRI (3T) feasibility experiments using high temperature resolution showed good correlation with transmitted power. In addition, T-matrix-based temperature increase predictions successfully demonstrated. As summary, an easy to implement, cheap, sensor-based method, the T-matrix, to investigate, characterize and mitigate RF heating of implants is introduced.          

Jerome L. Ackerman^1,2, Erez Nevo³, and Abraham Roth^3
1Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ²Department of Radiology, Harvard Medical School, Boston, MA, United States, ³Robin Medical, Inc., Baltimore, MD, United States

In magnetic resonance mediated radiofrequency ablation (MR-RFA) the RF energy for the ablation is captured by a wire antenna placed in the scanner bore, and channeled to the ablation needle. There are no external wired connections. The effective length of the antenna is adjusted physically or electrically to be resonant with the scanner RF to maximize energy capture. To suppress heating when desired, the antenna must be detuned. An electronic switch to do so reduces antenna efficiency, but a simple wireless hydraulically activated mechanical switch maintains full antenna efficiency and achieves high on-off ratio.

Andreas Port¹, Roger Luechinger¹, David Otto Brunner¹, and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland

Several stretchable conductor concepts have been proposed   that rely on a continuous metal phase, rigid or liquid, as conductive path. Conductive elastomers, fundamentally different, form the conductive path through contact between particles such as carbon nano tubes, silver nanowires or silver microparticles. In the present work, we explore the feasibility and performance of MR detection with conductive elastomer coils. Evaluation is performed in terms of Q, SNR and in-vivo imaging. The results indicate that MR receive coils made from conductive elastomer provide good stretchability, adequate electrical performance and promise workflow enhancements as such a coil could even be washed.

Florian Friedrich^1,2, C. Katharina Spindeldreier³, Juliane Hörner-Rieber³, Sebastian Klüter³, Peter Bachert^1,2, Mark E. Ladd¹, and Benjamin R. Knowles^1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Department of Physics and Astronomy, Heidelberg University, Heidelberg, Germany, ³Department of Radiation Oncology,, University Hospital of Heidelberg, Heidelberg, Germany

MR-linac hybrid systems can dynamically image a tumor during radiotherapy to aid in a more precise delivery of the radiation dose. Motion tracking of the target is required and is currently performed by a deformable image registration on Cartesian bSSFP images. This study compares three different tracking methods (convolutional neuronal network, multi-template matching, and deformable image registration) to track a lung tumor in Cartesian images, where the performance of the three methods did not differ significantly. The convolutional neuronal network provided minimal decrease in tracking accuracy in a healthy volunteer when undersampled radial images were used to accelerate image acquisition.