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Md Zahidul Islam¹, Ananda Kumar², Jianfeng Zheng¹, and Ji Chen^1
1Univ of Houston, Houston, TX, United States, ²FDA, Silver Spring, MD, United States

Keywords: Safety, Safety

The effect of ferrite magnetic beads to suppress the induced currents on a straight wire active implantable medical devices (AIMDs) lead was investigated. Leads with one, two and no ferrite beads were studied experimentally and using numerical simulations. The application of ferrite beads on the leads significantly reduced induced currents, and thus heating on experiments outside the MRI scanner. In the MRI magnet no significant reduction in heating was observed due to magnetic saturation of the ferrite beads. Suitable magnetic material for current suppression needs to be developed for application in MRI scanners.  

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Ali Caglar Özen¹, Maximillian Russe², Thomas Lottner¹, Simon Reiss¹, Sebastian Littin¹, Maxim Zaitsev¹, and Michael Bock^1
1Division of Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany, ²Department of Radiology, University Medical Center Freiburg, Freiburg, Germany

Keywords: Safety, Interventional Devices, Low Field, RF-induced heating

Low-field high-performance MRI systems at 0.55T are expected to cause less RF heating in conventional interventional devices compared to clinical 1.5T or 3T systems, which would facilitate MR-guided interventions significantly. Here we systematically evaluate the safety of intravascular devices through high-resolution electric field mapping, transfer function measurements, and realistic device trajectories from vascular models. Furthermore, the effects of patient size and positioning, target organ (liver and heart), and transmit body coil type are tested at a low-field RF test-bench for 6 commonly-used interventional devices (two guidewires, two catheters, an applicator and a biopsy needle).

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Pia Panravi Sanpitak¹, Bhumi Bhusal^1,2, Jasmine Vu^1,2, and Laleh Golestanirad^1,2
1Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States, ²Department of Biomedical Engineering, McCormick School of Engineering, Northwestern University, Evanston, IL, United States

Keywords: Low-Field MRI, Low-Field MRI, Simulations

Low-field MRI systems have been advertised as “safe” for patients with implants – but is this true? In a series of systematic simulations, we looked at implants with varied length, amount of coiling, and insulation during RF exposure in both 0.55 T and 1.5 T MRI environments. We found that both the actual and apparent length of the implant can significantly impact heating. There are several cases where heating is substantially higher at 0.55 T than 1.5 T, suggesting that no broad claims should be made, and these factors need to be carefully considered before scanning a patient.

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Finya Ketelsen^1,2 and Gregor Schaefers^1,3
1MRI-STaR - Magnetic Resonance Institute for Safety, Technology and Research GmbH, Gelsenkirchen, Germany, ²TU Dortmund University, Dortmund, Germany, ³MR:comp GmbH, Testing Service for MR Safety & Compatibility, Gelsenkirchen, Germany

Keywords: Safety, Safety, Implants, RF-induced heating

The novel open 64 MHz linear exposure system offers new possibilities for the test process of active implants for RF-induced heating as a safety issue. This study proves the concept, that the measurements for the validation process of the transfer function, which models the electric behavior of an active implant, could be accelerated from hours of precise work to minutes without any rearranging. Because the system is open, there is significantly more space than in a birdcage coil and the object and measuring probe can be mounted to a movement system, that can access the whole phantom.

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Lydia J Bardwell Speltz^1,2, Seung-Kyun Lee³, Yunhong Shu¹, Matt Tarasek³, Joshua D Trzasko¹, Thomas KF Foo³, and Matt A Bernstein^1
1Department of Radiology, Mayo Clinic, Rochester, MN, United States, ²Mayo Clinic Graduate School of Biomedical Sciences, Rochester, MN, United States, ³GE Global Research, Niskayuna, NY, United States

Keywords: Safety, Safety

We introduce a method to calculate lead-tip voltage for implanted devices by considering 1) the individualized lead path extracted from X-ray-based images, 2) the incident electric field per unit B₁+rms derived for the RF transmitter and a digital human body model, 3) the complex RF wavenumber in an insulated conductor derived from antenna theory.  T/R coil transmitters in whole-body at 1.5T and 3.0T were considered, as well as a head coil on a compact 3T.  Based on leads in 10 subjects, the results show the compact 3T produces less lead tip voltage than whole-body T/R coils.

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Simon Reiss¹, Ali Caglar Özen¹, Thomas Lottner¹, and Michael Bock^1
1Division of Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany

Keywords: Safety, Safety

Currently, no external defibrillation system is available that is labeled MR safe. To create an MR safe device heating induced by the electrodes that are attached to the patient needs to be prevented. In this study, we propose a setup for high resolution RF E-field mapping of commercially available defibrillation electrodes and show that this setup can be used to precisely detect hot spots. At these hot spots, we then perform temperature measurements within a 1.5T to assess the MR safety of the electrodes.

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Benson Yang¹, Fred Tam¹, Maryam Arianpouya², Cathleen Leone¹, Vicki Li¹, Jason Rock², and Simon Graham^1,2
1Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, ²Medical Biophysics, University of Toronto, Toronto, ON, Canada

Keywords: RF Arrays & Systems, New Devices

Parallel radiofrequency transmission (pTx) continues to show great promise in resolving MRI challenges at higher magnetic field strengths. Commercial pTx MRI systems can be very costly with limited system channel count options. This work presents the current state of an 8-channel pTx MRI system with expansion flexibility up to 32-channels that is based on software-defined radio technology.

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Bu S Park¹, Joshua Guag², Sunder Rajan², and Brent McCright^3
1FDA, Silver Spring, MD, United States, ²Division of Biomedical Physics (DBP), FDA, Silver Spring, MD, United States, ³Division of Cellular and Gene Therapies (DCGT), FDA, Silver Spring, MD, United States

Keywords: Safety, Electromagnetic Tissue Properties

This study describes a new method to improve RF safety of implantable medical devices located outside of the imaging region by using a secondary resonator (SR) to reduce electric fields and corresponding specific absorption rate (SAR) during MRI. The SR is designed to produce opposing electro-magnetic fields (EM-fields) compared to the EM-fields made by a body coil at 3.0T. This study was performed using numerical simulations with ASTM phantom and human models, and corresponding experimental verifications with the ASTM phantom.

Keywords: RF safety, secondary resonator

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Sukhoon Oh¹, Seon-Eui Hong², Hyung-Do Choi², Dongwoo Chang³, Kiseong Kim⁴, and Sangwoo Kim^5
1Korea Basic Science Institute, Cheongju, Korea, Republic of, ²Electronics and Telecommunications Research Institute, Daejeon, Korea, Republic of, ³Chungbuk National University, Cheongju, Korea, Republic of, ⁴BioBrain, Inc., Daejeon, Korea, Republic of, ⁵Daewon University College, Jechoen, Korea, Republic of

Keywords: Safety, Safety

Numerical investigations on the safety of patient assistants exposed to a 1.2T open MRI are performed at different poses of patient assistants (including wearing latex gloves), because current regulations are concerned with only patient RF safety. Compared with the patient, up to 29.8% of the patient 10-gram SAR was observed in the patient assistant. To prevent possible RF hazards of a patient assistant during MRI scans, certain clauses regarding the patient assistant’s poses or wearing gloves must be added to the existing MRI screening forms.

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Oliver Schad^1,2, Tobias Wech¹, and Herbert Köstler^1
1Department of Diagnostic and Interventional Radiology, University Hospital Würzburg, Würzburg, Germany, ²University of Würzburg, Experimental Physics 5, Würzburg, Germany

Keywords: Gradients, Safety, Peripheral Nerve Stimulation

The algorithm we present in this work designs variable density spiral (VDS) trajectories and their respective gradient time courses based on the Stanford VDS-tool. In addition to hardware limits (maximum gradient strength and slew rate) a PNS threshold based on the SAFE-Model is introduced. 

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Caroline Le Ster¹, Mikhail Kozlov², Alexandre Vignaud¹, and Nicolas Boulant^1
1University of Paris‐Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France, ²Department of Neurophysics, Max Plank Institut for Human Cognitive and Brain Sciences, Leipzig, Germany

Keywords: Safety, Thermometry

RF exposure during MR exams induces heating of the exposed tissues. Measurement of tympanic membrane temperature with an infrared sensor has been used to estimate non-invasively the global RF-induced temperature rise. In this study, the tympanic membrane temperature was measured before and after having the volunteers lying for 15 minutes with earplugs with neither an RF nor a static magnetic field. Large physiological variations of temperature rise were observed across the volunteers after this dummy “exposure”, showing the low reliability of this metric to measure small temperature rises, that make it problematic for RF-induced temperature rise estimation.

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Louai Aldayeh¹, Mizan Rahman¹, and Ross Venook^1
1Boston Scientific Neuromodulation, Valencia, CA, United States

Keywords: Safety, Safety

Previous investigations of RF-induced heating of multiple implants (active as well as passive) have shown that heating of an implant can be impacted by the presence of a separate neighboring implant.

This work assessed to which extend this phenomenon is present for the limited scope of two separate MR Conditional ipsilateral DBS implants, one on one side of the body, and another on the other side. Both, RF-induced heating and voltage injection level into the IPG were assessed.

A variety of DBS lead configurations, and clinically relevant distances in-between the two separate implants, were thoroughly assessed for a data-driven conclusion.

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Michael Childers¹, Dorab Sethna¹, and Shiloh Sison^2
1Abbott, Sylmar, CA, United States, ²Abbott, Sunnyvale, CA, United States

Keywords: Safety, Safety, Implants

Simulations were performed to assess potential gradient induced vibration of leadless pacemakers. Results of the evaluation showed leadless pacemakers sized objects, made from commonly used conductive materials, generated very small vibrations (all less than 0.3mm in displacement) when exposed to conservative gradient induced vibration safety test conditions per ISO/TS 10974. These calculated displacements are negligible in comparison to the interacting displacements between a typical leadless pacemaker and cardiac tissue through each cardiac cycle. As such, the risk of leadless pacemaker gradient induced vibration tissue damage is minimal and assessments for this hazard per ISO/TS 10974 may not be necessary.

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Michael JB McGrory¹, Edwin Versteeg¹, Jeroen CW Siero^1,2, and Dennis WJ Klomp^1
1Radiology, University Medical Center Utrecht, Utrecht, Netherlands, ²Spinoza Center for Neuroimaging, Amsterdam, Netherlands

Keywords: Gradients, Gradients

Large dB/dt swings in gradient coils can induce peripheral nerve stimulation (PNS) in the human body. This limits the slew rates used in whole-body MRI reducing scan speeds and spatial resolution. Ultrasonic head gradients can enable fast and silent imaging, however extension to whole-body gradients is challenging due to the required larger dB/dt swings. In this work, we present a body gradient coil which can be used to investigate PNS induction at an ultrasonic driving frequency of 20kHz.

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Caroline Le Ster¹, Erwan Selingue¹, Roseline Poirier², Jean-Marc Edeline², Sébastien Mériaux¹, and Nicolas Boulant^1
1University of Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France, ²University of Paris-Saclay, CNRS, NeuroPSI, Saclay, France

Keywords: Bioeffects & Magnetic Fields, Animals

High static magnetic (B0) fields are known to induce a transient disturbance of the inner ear. Recently a study demonstrated long-term behavioural effects in mice chronically exposed to a B0 field of 16.4T. In the current study, mice underwent chronic B0 exposure at 11.7T or 17.2T and longitudinally performed behavioural tests over the study. An auditory brainstem response (ABR) test was performed at the end of the full exposure period to assess inner ear properties. Despite the transient disturbance of mice inner ear observed immediately after B0 exposure, no short-term or long-term alteration was detected with behavioural or ABR tests.

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Tobias Gilk^1,2
1Gilk Radiology Consultants, Overland Park, KS, United States, ²RADIOLOGY-Planning, Kansas City, MO, United States

Keywords: Safety, Safety

US data suggests that MRI adverse events are growing at a rate of nearly 3x the rate of MRI examinations. While MRI accidents and injuries remain infrequent, the long-term trend of significant growth in MRI adverse events highlights needs for vigilance in MRI safety.

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Feng Jia¹, Sebastian Littin¹, Philipp Amrein¹, Maximilian Frederik Russe², and Maxim Zaitsev^1
1Division of Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany, Freiburg, Germany, ²Department of Radiology, University Medical Center Freiburg, Freiburg, Germany, Freiburg, Germany

Keywords: Safety, Safety, PNS Simulation

Simulation of peripheral nerve stimulation of MRI gradient coils for rotated arms of an interventional radiologist. The arm rotation has a direct influence on the site of stimulation in the arm.