Benson Yang¹, Maryam Arianpouya², Aaron Loh³, Gavin Elias³, Artur Vetkas³, Can Sarica³, Brendan Santyr³, and Simon J Graham^1,2
1Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, ²Medical Biophysics, University of Toronto, Toronto, ON, Canada, ³Surgery, University of Toronto, Toronto, ON, Canada

High SAR RF pulse sequences continue to be avoided for patients with implanted deep brain stimulation (DBS) devices, due to the increased risk of injury. Recent studies have shown that DBS lead management can impact electromagnetic behavior and thus, the overall RF heating effects along the implanted device. The present work studied two patient-based DBS lead trajectories using a commercial DBS device with MR-conditional labeling for full-body 3 T MRI, implanted in a novel anthropomorphic phantom. The preliminary results showed temperature elevations that exceed current imaging guidelines remains possible for high SAR RF pulse sequences.

Noa Beth Nuzov¹, Bhumi Bhusal², Fuchang Jiang¹, Joshua Rosenow³, 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

Deep Brain Stimulation (DBS) implants are implanted into target regions of the brain to treat symptoms of many neurological disorders. Postoperative Magnetic Resonance Imaging (MRI) scans are used to localize DBS leads, however, there are large, distorted artifacts surrounding the leads in the images. This study uses MRI phantoms to investigate the true location of a DBS lead relative to its artifact. The results will help researchers and clinicians know the actual locations of the lead tip and contacts from postoperative MRI scans to confirm the implant is correctly targeting the desired brain area.

Lena Kranold^1,2, Tolga Goren¹, Sunder Rajan³, and Niels Kuster^1,2
1IT'IS Foundation, Zurich, Switzerland, ²Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich, Switzerland, ³Center for Devices and Radiological Health (retired), FDA, Silver Spring, MD, United States

Anthropomorphic computational phantoms are used to numerically estimate the potential envelope of intensity and distribution of induced E-fields in patients undergoing MR examination. The impact of anatomical variation of the phantom on medical implant risk assessment is demonstrated for generic transfer functions and lead trajectories representing pacemaker, DBS, SCS, and cochlear implant routings. Results showed that even when only one generic transfer function was considered, each of the 12 anatomical phantoms represented the worst-case for at least one configuration. Thus, the widest available range of anatomical phantoms must be examined to define a conservative safety envelope. 

Vincent Hammersen¹, Michael Wolff², Andreas Rennings³, and Gregor Schaefers^1,2
1MRI-STaR GmbH, Gelsenkirchen, Germany, ²MR:comp GmbH, Gelsenkirchen, Germany, ³General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, Duisburg, Germany

MR safety of AIMD with leads is assessed test procedures defined in ISO/TS10974. This separates the different electromagnetic field interactions into independent test procedures. E.g., malfunction and rectification testing, with gradient and RF injection networks connected to the lead ports of AIMDs. But this does not correspond to "realistic MRI exposures", where a precise combination of RF and magnetic fields is used for imaging. For this reason, a concept is being proposed in which both injection networks are combined to allow a concerted exposure. This allows the simultaneous exposition of any gradient and RF signal combination.

Koray Ertan^1,2, Paolo Decuzzi², Peter B Roemer³, and Brian Rutt^1
1Department of Radiology, Stanford University, Stanford, CA, United States, ²Laboratory of Nanotechnology for Precision Medicine, Italian Institute of Technology, Genoa, Italy, ³Roemer Consulting, Lutz, FL, United States

Either peak E-fields on simple geometries with uniform interior properties as suggested by IEC or coupled E-field and neurodynamic simulations on realistic body models can be employed in PNS optimal gradient coil design. Magneto quasi-static simulations were performed to compare the magnitude and location of the peak E-fields in uniform interior body models with smoothed or realistic surface features to fully heterogeneous Virtual Family models. Although peak E-fields are higher on the heterogeneous body models due to complex tissue interfaces, simplified and/or homogeneous models represent a more practical and robust approach predicting population-wide PNS performance.

Angelo Galante^1,2,3, Valentino Vito³, Elia Braggio⁴, Roberta Milanesi⁴, Vincenzo Giugno⁵, and Marcello Alecci^1,2,3
1Consiglio Nazionale Ricerche - Istituto SPIN, L'Aquila, Italy, ²Istituto Nazionale Fisica Nucleare - Laboratori Nazionali del Gran Sasso, L'Aquila, Italy, ³Università dell'Aquila, L'Aquila, Italy, ⁴Tecnorad SrL, Verona, Italy, ⁵Azienda Sanitaria Locale 1 - Abruzzo, L'Aquila, Italy

We show how to monitor the MRI staff exposure to the $$$B_0$$$ stray-field. Monitoring is extended to several body districts without interferences with normal hospital operative procedures. The Weighted Peak index is calculated, for different Action Levels limits as from the current EU regulations, to consider the non-sinusoidal nature of exposure. Results show that exposure limits are exceeded even at 1.5 T and their occurrences significantly increase at 3.0 T scanners.

Mostafa Berangi^1,2,3, Andre Kuehne¹, Helmar Waiczies¹, and Thoralf Niendorf^1,2,3
1MRI.TOOLS GmbH, Berlin, Germany, ²Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, berlin, Germany, ³Charité – Universitätsmedizin Berlin, berlin, Germany

MRI aided monitoring of (biodegradable) passively conducting implants is challenged by transmission field inhomogeneities and potential elevation of RF power deposition (SAR) in the vicinity of an implant. Small movements of an implant with respect to the RF transceiver constitute another potential risk factor for clinical MRI. Recognizing this challenge and the opportunities, this work uses a multi-objective genetic algorithm (GA) to examine the feasibility of excitation vector optimized parallel transmission in the presence of small variations in implant position/orientation. The GA approach provided excitation vectors that meet the safety guidelines for SAR in close vicinity of a (biodegradable) passively conducting implant and that are immune to small changes in the relative position between the implant and the RF transceiver. Our findings are not limited to the specific implant configurations and experimental setups used in this study but provide the technical foundation to derive a generalized transfer function.

Pia Panravi Sanpitak¹, Bhumi Bhusal¹, Bach Nguyen¹, Fuchang Jiang², Ehsan Kazemivalipour^3,4, Giorgio Bonmassar^3,4, Julie Pilitsis⁵, Joshua Rosenow⁶, Gregory Webster⁷, Andrada Popescu⁸, Daniel Kim¹, and Laleh Golestanirad^1,2
1Department of Radiology, Northwestern University, Chicago, IL, United States, ²Department of Biomedical Engineering, Northwestern University, Evanston, IL, United States, ³A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ⁴Harvard Medical School, Boston, MA, United States, ⁵Department of Neurosciences & Experimental Therapeutics, Albany Medical College, Albany, NY, United States, ⁶Department of Neurosurgery, Northwestern University, Chicago, IL, United States, ⁷Division of Cardiology, Department of Pediatrics, Northwestern University, Chicago, IL, United States, ⁸Department of Medical Imaging, Lurie Children's Hospital, Chicago, IL, United States

Low-field Magnetic Resonance Imaging (MRI) systems are gaining traction, but their impact on radiofrequency (RF) heating of elongated implants is unclear. The RF heating of conductive lead models with realistic trajectories was examined inside a 1.5 T MRI coil and a 0.55 T Wide Bore MRI coil. 0.1g-SAR was recorded at the tips of conductive implanted leads in adult patients with deep brain stimulation (DBS) systems and pediatric patients with cardiac implants, at both chest and head landmarks. In some instances, heating was higher in the 0.55 T coil, so caution must be exercised before promoting low-field coils as "implant-friendly".

Xuchen Zhu¹, Wenbo Sun², Shuo Zhu^3,4, Zhenhua Shen¹, Lan Lan², Shihong Han¹, Shuheng Zhang¹, Zhang Shi^3,4, Qi Liu⁵, Yongquan Ye⁵, Liang Liang^3,4, Haibo Xu², and Liang Liu^1
1United Imaging Healthcare, Shanghai, China, ²Department of Radiology，Zhongnan Hospital of Wuhan University, Wuhan, China, ³Department of Radiology, Zhongshan Hospital, Fudan University, Shanghai, China, ⁴Shanghai Institute of Medical Imaging, Shanghai, China, ⁵UIH America, Inc., Houston, TX, United States

 Questionnaires on subjective feeling were collected and analyzed from 202 subjects following whole-body MRI examinations at 5T. No intolerable discomfort was reported, indicating whole-body examinations at 5T is safe when necessary safety protocols were followed.  

Amgad Louka^1,2, William Bradfield-Handler^2,3, and Blaine Chronik^1,2,3
1Medical Biophysics, Western University, London, ON, Canada, ²The xMR Labs, Western University, London, ON, Canada, ³Physics & Astronomy, Western University, London, ON, Canada

We have developed a novel perfusion phantom and this work describes the simulated RF-heating of a 10 cm titanium rod inside this phantom when placed inside the current gold standard (ASTM) phantom, and our geometry/muscle-mimicking phantoms. Simulations show a 30-45% decrease in observed heating due to perfusion cooling, and once these simulations are experimentally validated they could pave the way for improved acceptance criteria and ultimately improved patient access to MRI
 

Mikhail Kozlov¹ and Nicolas Boulant ^2
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ²Université Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-Sur-Yvette, France

We derived analytical steady-state and transient solutions for a sphere and a SAR source with uniform and the Gaussian distribution located in an infinite medium of homogeneous properties. The results obtained analytically showed  that even without taking into account blood perfusion (i) if power deposition is present only in a sphere that encloses 10 gram of human tissue and SAR_10g=10W/kg the steady-state temperature rise is below 3°C for power deposition distributions as sharp as Gaussian with σ=R/3=4.33mm, (ii) the sharper the Gaussian distribution of power deposition, the higher T_max(t=+∞) and the faster it will approach steady-state.

Amira Trabelsi^1,2,3, Megdouda Benamara⁴, Pierre Jomin¹, Stefan Enoch¹, Marc Dubois⁴, Martine Pithioux³, David Bendahan², and Redha Abdeddaim^1
1Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, Marseille, France, ²Aix Marseille Univ, CNRS, CRMBM, Marseille, France, ³Aix Marseille Univ, CNRS, ISM, Marseille, France, ⁴Multiwave Imaging, Marseille, France

We assessed electromagnetic behavior of metallic implant used for distal femur fracture in typical MRI situation. |B₁⁺| field, SAR and temperature variations were computed at 3T using a surface coil on human model for different positions of the implant relative to the coil. To validate the simulation, we measured the E-field and compared it to simulated E-field. |B₁⁺| field maps showed an interesting augmentation near the implant. Both global SAR and local SAR levels proved that it is possible to safely image bone repair. However, temperature elevation near the tip of the implant was important and is to be considerate.

Oriano Bottauscio¹, Alessandro Arduino¹, Fabio Baruffaldi², Mario Chiampi¹, Jessica Martinez¹, Umberto Zanovello¹, and Luca Zilberti^1
1Advanced Materials Metrology and Life Science, Istituto Nazionale di Ricerca Metrologica, Torino, Italy, ²IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy

In silico evaluation of heating during an MRI exam for patients with passive implants patients need detailed anatomical models to reproduce in vivo scenarios. A quantification of the influence of the model approximation is fundamental to define the main requirements of the digital model.Here, we analyze the impact of different model approximation in simulating RF and gradient-induced heating caused by orthopedic implants. It was found that, whereas the heating due to switched gradient fields does not strictly require the adoption of advanced virtual surgery, the heating caused by RF is strongly affected by the precision of the digital model.

Mikhail Kozlov¹, Wolfgang Kainz², and Manuel Murbach^3
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ²U.S. FDA, CDRH, Office of Science and Engineering Laboratories, Division of Biomedical Physics, Silver Spring, MD, United States, ³EMConsulting, Zurich, Switzerland

The safety assessment of RF exposure in MRI heavily relies on electromagnetic simulations. As there are numerous different coil designs on the market, this assessment is typically performed with sets of generic coil geometries to cover the commercially available bore diameter and coil lengths. This abstract investigated the effect of other design parameters, which are currently less considered. Our results show that feed-port positioning and non-ideal tuning of the coil may considerably alter the RF absorption pattern in an oval phantom, and even more so the E-field distribution outside the phantom.

Agazi Samuel Tesfai¹, Simon Reiss¹, Thomas Lottner¹, Andreas Vollmer², Michael Bock¹, and Ali Caglar Özen ^1
1Dept. of Radiology, Medical Physics, Medical Center – University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany, ²Department of Oral and Craniomaxillofacial Surgery, Center for Dental Medicine, University Medical Center Freiburg, Freiburg, Germany

Intraoral coils (IOCs) increase the signal-to-noise ratio in dental MRI exams several times over external coils. However, the intraoral coil placement might be associated with safety hazards such as RF heating. This study evaluates the safety of different IOCs using temperature and E-field measurements to detect temperature hotspots. An inductively-coupled and a wired IOC were constructed, E-field hotspots were detected and the temperature increase was measured showing that it remains below 1K over 6min RF exposure.