Jasmine Vu^1,2, Bach T Nguyen², Bhumi Bhusal², Justin Baraboo^1,2, Joshua Rosenow³, Ulas Bagci ², Molly G Bright^1,4, and Laleh Golestanirad^1,2
1Biomedical Engineering, McCormick School of Engineering, Northwestern University, Evanston, IL, United States, ²Radiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States, ³Neurosurgery, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States, ⁴Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States

Safety risks associated with radiofrequency (RF) heating of tissue around implanted leads limit MRI accessibility for patients with active electronic implants such as those with deep brain stimulation (DBS) devices. RF heating is highly sensitive to the trajectory of the implanted lead, and full-wave electromagnetic simulations are currently the standard method for quantifying RF heating, requiring extensive computational resources and simulation time. Here, we present a promising, fast approach for predicting trajectory-specific maximum local specific absorption rate (SAR) in the tissue around tips of implanted lead models using deep learning. 

Seoggwan Kim¹, Amy Kester¹, Alan R. Leewood¹, and David C. Gross^1
1MED Institute Inc., West Lafayette, IN, United States

The goal of this study was to develop a computational model that can accurately predict the radiofrequency (RF) induced temperature rise of medical devices in a 1.2T (49 MHz) Hitachi Oasis open bore system for the purpose of MRI labeling according to ASTM F2503. A comparison of experimental and analytical temperature rise of calibration rods, a stent, and a knee implant within a gel phantom was conducted.  Simulations of RF heating of the stent and knee implant within the Duke virtual human model were compared for the 1.2T Hitachi Oasis open bore and 1.5T Siemens Avanto closed bore MRI systems.

David Prutchi¹, Jason Meyers¹, and Ramez Shehada^2
1Impulse Dynamics (USA) Inc., Marlton, NJ, United States, ²Medical Technology Laboratories, La Mirada, CA, United States

RF-induced heating of an active implantable medical device (AIMD) composed of a pulse generator (IPG) and leads depends on the transmission line impedance of the lead and its proximal-end termination by the impedance of the IPG.   We demonstrate that the RF impedance of IPGs is minimal relative to that of the leads, which dominates the overall impedance of the implantable system.    Accordingly, mixed hybrid systems composed of MR-Conditional leads and any MR-conditional IPG are expected to have a comparable overall impedance and consequently produce the same RF-induced heating as their corresponding original systems specified by the manufacturers.

David Prutchi¹, Jason Meyers¹, and Ramez Shehada^2
1Impulse Dynamics (USA) Inc., Marlton, NJ, United States, ²Medical Technology Laboratories, La Mirada, CA, United States

This study investigates the change in the RF filtering characteristics of the leads of active implantable medical devices (AIMDs) as body fluids seep into the leads during the initial post-implant period.  Our findings indicate that the RF characteristics change dramatically with fluid absorption, making it necessary to precondition the leads by soaking in isotonic saline solution to simulate the in-vivo scenario when conducting in-vitro MR safety testing. Furthermore, leads designed with RF-attenuating lumped inductances must consider the effect of fluid absorption on changing the peak RF attenuation frequency.

Kyoko Fujimoto¹, Tayeb A Zaidi¹, Dave Lampman², Josha W Guag¹, Shawn Etheridge², Hideta Habara³, and Sunder S Rajan^1
1Center for Devices and Radiological Health, US Food and Drug Administration, Silver Spring, MD, United States, ²Hitachi Healthcare Americas, Twinsburg, OH, United States, ³Healthcare Business Unit, Hitachi, Ltd., Tokyo, Japan

Radio-Frequency (RF) induced thermal injury is a common adverse event reported to US Food and Drug Administration. RF-induced heating risk depends on the interaction of implantable medical devices with electric field distribution in the MRI systems. A study showed that RF-induced heating of a neuromodulation device was much lower in the planar system compared to the cylindrical system. In this study, the hip and knee implants were studied in an anatomical human model at a 1.2T planar system and a 1.5T cylindrical system.

Finya Ketelsen^1,2, Kevin Kröninger², 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 Services for MR Safety & Compatibility, Gelsenkirchen, Germany

To determine the RF-induced heating of implants, it is necessary, that the RF field source used for testing fulfills several requirements. This study introduced the validation of a new developed linear exposure system for testing.
The results for E-Field distributions from numerical simulations are validated experimentally by measuring these E-field distributions. Furthermore, the temperature rise at the 100mm titanium rod is compared with the target values form ISO/TS 10974 Annex I.
The system fulfills the requirements and is suitable for testing active and passive implants for RF-induced heating according to ASTM F2182 and ISO/TS 10974.

Mark BM Hofman¹, Cristina Lavini², Albert van der Zwan³, Carola van Pul⁴, Sara H Muller⁵, Mette K Stam⁶, Marinette van der Graaf⁷, Carla Kloeze⁸, Bastiaan J van Nierop⁹, Wouter Teeuwisse¹⁰, Peter Kappert¹¹, Evie EM Kolsteren¹², Kristie Venhorst¹², and Joost PA Kuijer^13
1Radiology and Nuclear Medicine, Amsterdam UMC, Vrije Universiteit, Amsterdam, Netherlands, ²Radiology and Nuclear Medicine, Amsterdam UMC location AMC, Amsterdam, Netherlands, ³, Neurology and Neurosurgery, UMC Utrecht Brain Center, Utrecht, Netherlands, ⁴Maxima Medical Centre, Eindhoven, Netherlands, ⁵Antoni van Leeuwenhoek Hospital, Amsterdam, Netherlands, ⁶Radiology, LUMC, Leiden, Netherlands, ⁷Imaging, Radboud UMC, Nijmegen, Netherlands, ⁸Catharina Hospital, Eindhoven, Netherlands, ⁹Radiology and Nuclear Medicine, University Medical Centre Utrecht, Utrecht, Netherlands, ¹⁰CJ Gorter Center for High Field MRI, LUMC, Leiden, Netherlands, ¹¹Radiology, UMCG, Groningen, Netherlands, ¹²Knowledge Institute Medical Specialists, Utrecht, Netherlands, ¹³Radiology and Nuclear Medicine, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, Netherlands

The Dutch Association of Medical Specialists wrote a guideline for MR safety experts for an MRI examination in a patient with a cerebral aneurysm clip for known and unknown clip types. Risk stratification for unknown clip types was based on a survey in the Netherlands that identified time frames and locations of ferromagnetic clip use.

Jessica A. Martinez¹ and Daniel B. Ennis^1,2,3
1Department of Radiology, Stanford University, Stanford, CA, United States, ²Cardiovascular Institute, Stanford University, Stanford, CA, United States, ³Maternal & Child Health Research Institute, Stanford University, Stanford, CA, United States

Pediatric patients with cardiac implantable electronic devices (CIEDs) are generally contraindicated for MRI exams. Previous work in the adult population suggests that RF heating strongly depends on the patient’s position and orientation within the MRI scanner. The objective of this work was to evaluate in silico several pediatric patient-positions within the MRI scanner as methods to reduce RF-heating.

Hongbae Jeong^1,2 and Giorgio Bonmassar^1,2
1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ²Department of Radiology, Massachusetts General Hospital/Harvard Medical School, Boston, MA, United States

In this study, RF heating of an EEG on a 29-month-old whole-body voxel model in a 3T MRI was studied with numerical simulation using Sim4Life. 128-channel EEG leads and electrodes were drawn on the head of the 29-month-old voxel model, and the position of the EEG electrodes was estimated from the 3D scan of the EEG net. The 10gSAR_max and the SAR_head were assessed in the model with and without the EEG net in birdcage transmit body coil at 3T. In both cases, estimated results of SAR were well-below the RF safety limit in the international standard.

Rüdiger Brühl¹, Thomas Schwenteck¹, Bernd Ittermann¹, Fabio Baruffaldi², Alessandro Arduino³, Umberto Zanovello³, Luca Zilberti³, Mario Chiampi³, and Oriano Bottauscio^3
1Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany, ²IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy, ³Istituto Nazionale di Ricerca Metrologica (INRIM), Torino, Italy

Switching MR gradients induce eddy-currents in metallic implants. Gradient-aggressive MR sequences were used on a commercial 3 T scanner to heat orthopaedic prostheses ex vivo. Heating experiments are presented, and the measured temperature evolution is compared with corresponding numerical results. Numerical simulations have been successfully validated for five MR sequences at different implant position and orientations in the gradient field.

Vincent Hammersen¹, Finya Ketelsen¹, Andreas Rennings², and Gregor Schaefers^1,3
1MRI-STaR Magnetic Resonance Institute for Safety Technology and Research GmbH, Gelsenkirchen, Germany, ²General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, Duisburg, Germany, ³MR:comp GmbH, Gelsenkirchen, Germany

RF-induced heating of implants is strongly dependent on the E-Field magnitude at the test location, which is why a universal ±1dB and ±20° phase shift target field value limit is applied. We used numerical simulation to vary the exposing E-Fields, while keeping a constant average E-field magnitude at the test location. Strong deviations in heating development could be observed. In a second step we added phase shifts between exposition sources.

The results suggest that, in addition to the limits, the exact field distribution especially the E-field directions should also be taken into account in critical inhomogeneous cases.

Mubashir Hussain¹ and Gregor Schaefers^1,2
1Magnetic Resonance Institute for Safety, Technology and Research GmbH, Gelsenkirchen, Germany, ²MR:comp GmbH, Testing Services for MR Safety & Compatibility, Gelsenkirchen, Germany

This work focus on estimating the RF-induced deposited power at the multi-electrode array of cortical implant (CorTec GmbH, Germany) by means of lead electromagnetic models (LEM). To develop the LEM for such a complex structure, we computed the transfer function for each of the electrode and generated a set of artificial tangential electric fields for validation of the LEM. The transfer functions and the tangential electric fields along the leads are then used to develop the LEM which can estimate the deposited power at the electrode array for an arbitrary lead pathway.  

Paul Mcelhinney¹, Sarah Allwood-Spiers², Gavin Paterson¹, Marios Philiastides¹, and Shajan Gunamony^1
1University of Glasgow, Glasgow, United Kingdom, ²NHS Greater Glasgow and Clyde, Glasgow, United Kingdom

Simultaneous use of EEG and fMRI at high fields (UHF, ≥7T) offers the dual benefits of a high spatial resolution as well as the ability to study dynamic brain processes. A close fitting coil design has been built for this purpose, having open access to the subject and the EEG hardware while maintaining excellent performance characteristics. We present here the results from computer simulations of the head coil, including the EEG cap using human body models for safety validation and optimization of the design.

Mark BM Hofman¹, Carla Kloeze², Bastiaan J van Nierop³, Sara H Muller⁴, Joost PA Kuijer¹, Kristie Venhorst⁵, Cristina Lavini⁶, Mette K Stam⁷, Carola van Pul⁸, Wouter Teeuwisse⁹, Marco JW Gotte¹⁰, Peter Kappert¹¹, Evie EM Kolsteren⁵, and Marinette van der Graaf^12
1Radiology and Nuclear Medicine, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, Netherlands, ²Catharina Hospital, Eindhoven, Netherlands, ³Radiology and Nuclear Medicine, University Medical Centre Utrecht, Utrecht, Netherlands, ⁴Antoni van Leeuwenhoek Hospital, Amsterdam, Netherlands, ⁵Knowledge Institute Medical Specialists, Utrecht, Netherlands, ⁶Radiology and Nuclear Medicine, Amsterdam UMC location AMC, Amsterdam, Netherlands, ⁷Radiology, LUMC, Leiden, Netherlands, ⁸Maxima Medical Centre, Eindhoven, Netherlands, ⁹CJ Gorter Center for High Field MRI, LUMC, Leiden, Netherlands, ¹⁰Cardiology, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, Netherlands, ¹¹Radiology, UMCG, Groningen, Netherlands, ¹²Imaging, Radboud UMC, Nijmegen, Netherlands

Can a patient with a prosthetic heart valve, annuloplasty ring or a mitra clip undergo an MRI examination? The Dutch Association of Medical Specialists (FMS) wrote a guideline, using searches of guidelines, literature, implant databases, and incident databases. The recommendation is: scan the patient with a prosthetic heart valve, annuloplasty ring or mitra clip with an 1.5T or 3T whole body MRI system with a horizontal closed bore superconducting magnet without further restrictions.

Negin Behzadian¹ and Shiloh Sison^2
1Research and Development, Abbott, Sylmar, CA, United States, ²Research and Development, Abbott, Sunnyvale, CA, United States

MRI RF heating can cause thermal damage to biological tissues, especially in patients with leaded implantable devices, by concentrating power deposition at the implant-tissue interface. With the emergence of B_1+RMS as a more precise RF exposure metric than SAR, implantable device manufacturers have begun MR conditional labeling to fixed B_1+RMS levels, in addition to SAR labeling. Our study characterizes the relationship between RF heating per SAR vs. B_1+RMS-based scaling methods in the context of 3T Normal Operating and First Level Controlled Mode MRI exposure.

Camille D.E. Van Speybroeck¹, Wouter M. Teeuwisse¹, Tom O'Reilly¹, Paul M. Arnold², and Andrew G. Webb^1
1G.J. Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, Netherlands, ²Neurosurgery, Carle Foundation Hospital, Urbana, IL, United States

Very little quantitative data exist on safety aspects of medical implants in low field MRI systems. Protocols for clinical scanners must be adjusted due to differences in bore size and B₀ direction. We present measured and simulated data on magnetically induced displacement forces, image artifacts and SAR on a 50 mT portable MRI system. Results show that some implants must be considered MR unsafe even at 50 mT, that image artifacts are less compared to 3 T even with much lower gradient strengths, and SAR limits can be breached if using very short pulses and inter-echo times in TSE sequences.

Peter Stijnman^1,2, Arcan Erturk³, Cornelis van den Berg¹, and Alexander Raaijmakers^1,2
1Computational Imaging, UMC Utrecht, Utrecht, Netherlands, ²Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands, ³Medtronic, Minneapolis, MN, United States

A new method to validate the transfer function (TF) of linear implants was developed, using an independent RF transmitter. A simulation study was performed exploring different methods to change the incident electric field, local transmit coils positioned at various locations is most effective for the validation. A benefit is the constant position of the leap tip and the temperature probe. We performed a TF measurement and validation study for three leads. The simulated incident electric fields of the local transmit coils and the measured TF were used to predict tip heating, verified by temperature probe measurements showing excellent agreement ($$$R^2\geq0.977$$$).

Yuqing Wan¹, Nathan Ooms², Paul Nguyen¹, and Guangqiang (Jay) Jiang^1
1Axonics Modulation Technologies, Irvine, CA, United States, ²Purdue University, West Lafayette, IN, United States

This study reported magnetic resonance imaging (MRI) examination duration of 974 patients collected from two imaging sites. Statistical scan time analysis was performed, and distributions were obtained for different scan regions. Scan time disparities were found between the two imaging sites due to the sequence selections and configuration, which may impact imaging cost and image quality. The clinical examination duration data provides useful information for implant device manufacturers to define  practical MRI conditions that improve the patients’ overall MR experience.

Benson Yang^1,2, Fred Tam¹, Benjamin Davidson³, Clement Hamani^3,4, Nir Lipsman^1,3,4, Chih-hung Chen², and Simon J Graham^1,5
1Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, ²Electrical and Computer Engineering, McMaster University, Hamilton, ON, Canada, ³Division of Neurosurgery, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁴Harquail Centre for Neuromodulation, Sunnybrook Research Institute, Toronto, ON, Canada, ⁵Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada

Magnetic resonance imaging of deep brain stimulation (DBS) patients remains a safety concern at higher magnetic fields strengths. Phantoms play an important role in validating and estimating patient safety conditions. However, conventional phantoms are typically simple homogeneous structures that limit the ability to replicate DBS surgical implant procedures. In this work, a new phantom structure is proposed with more human-like realism and compartments to enable improved replication of DBS device placement geometries. Preliminary radiofrequency heating results demonstrate significant differences in temperature elevations when the phantom is assembled in a heterogeneous and homogeneous configuration.