Volkan Acikel¹, Patrick Magrath^1,2, Scott E Parker¹, Holden H Wu¹, Peng Hu¹, Paul J Finn¹, and Daniel B Ennis^1,2
1Department of Radiological Sciences, University of California Los Angeles, Los Angeles, CA, United States, ²Department of Bioengineering, University of California Los Angeles, Los Angeles, CA, United States

MRI exams for patients with pacemakers and implanted cardioverter defibrillators (ICDs) are contraindicated at all clinical field strengths.  The aim of this study was to measure directly RF induced lead tip heating during MRI exams of cadavers with existing devices at both 1.5T and 3T.

Berk Silemek¹, Oktay Algin^1,2, Cagdas Oto³, and Ergin Atalar^1,4
1UMRAM, Bilkent University, Ankara, Turkey, ²Department of Radiology, Atatürk Education and Research Hospital, Ankara, Turkey, ³Faculty of Veterinary Medicine, Ankara University, Ankara, Turkey, ⁴Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey

RF tissue heating of the Active Medical Implantable Devices (AIMD) is a well-known problem. However, due to the complex structure of the body, in vivo testing of the AIMDs’ heating under MRI cannot be verified with phantoms completely. Acute in vivo experiments damage the tissue and body’s thermoregulation response changes which can affect the measurements and investigation of the problems. Here, we propose a Temperature Sensor Implant setup to eliminate hyperacute effects of the surgery and enable real-time temperature monitoring of the tip of the implant during MRI examination

Earl Zastrow^1,2, Myles Capstick^1,3, and Niels Kuster^1,2
1IT'IS Foundation, Zurich, Switzerland, ²Department of Information Technology and Electrical Engineering, ETH-Zurich, Zurich, Switzerland, ³Zurich MedTech AG, Zurich, Switzerland

Patients with elongated conductive implants are generally excluded from MRI diagnostics because the interaction of the implant with MRI-induced RF fields can lead to hazardous localized heating in surrounding tissues. Depending on the complexity of the lead structure, numerical assessment of implant-RF interactions may require excessive computational overhead and may not be feasible. To overcome this challenge, an experimental system, based on the revised Tier 3 of the ISO/IEC TS 10974, is developed and validated with full-wave electromagnetics simulations. The experimental system is designed for the assessment of RF-induced heating of implants, irrespective of the complexity of the implant structure.

Earl Zastrow^1,2, Juan Córcoles³, and Niels Kuster^1,2
1IT'IS Foundation, Zurich, Switzerland, ²Department of Information Technology and Electrical Engineering, ETH-Zurich, Zurich, Switzerland, ³Department of Electronic and Communication Technology, Universidad Autónoma de Madrid, Madrid, Spain

Interactions of long insulated implants with conductive wires (e.g., cardiac pacemaker and deep-brain stimulator) with RF during MRI can lead to excessive local heating of tissue at the vicinity of the implant and is one of the contraindication to MRI. We present the preliminary results of a convex optimization method that can be used to suppress the local deposited power in tissue in a controllable manner. The performance of the proposed method is evaluated, as a function of the trade-off between homogeneity of |B₁⁺| and the mitigated RF-induced power deposition caused by the implant, for multiple clinical scenarios at 128 MHz.

David C. Gross^1,2, Benjamin Scandling¹, and Orlando P. Simonetti^3,4
1Biomedical Engineering, The Ohio State University, Columbus, OH, United States, ²Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, OH, United States, ³Radiology, The Ohio State University Wexner Medical Center, Columbus, OH, United States, ⁴Internal Medicine, Division of Cardiovascular Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States

The goal of this study was to investigate the influence of blood flow on the temperature rise of a peripheral vascular stent during MRI with flow phantom experiments and computer simulations. RF heating experiments of a vascular stent are performed during MRI at 3.0T in a flow phantom.  The temperature rise of the stent is measured with varied flow rates.  The temperature rise of the stent was over 10°C without flow, and was reduced by 50% with a flow rate of only 50 mL/min.  Blood flow significantly reduces the temperature rise of stents and the surrounding tissue during RF heating.  

Peter Serano^1,2, Maria Ida Iacono¹, Leonardo M. Angelone¹, and Sunder S. Rajan^1
1U.S. Food and Drug Administration, Washington, DC, United States, ²Electrical and Computer Engineering, University of Maryland, College Park, MD, United States

In this study, the authors present an analysis of a potentially overlooked clinical scenario, namely overlapped stents separated with a layer of insulation. Electromagnetic and thermal simulations as well as measurements were performed to test such configurations. The results show that implanted medical devices that include gapped conductive structures, like overlapped stents, can affect the location and magnitude of peak heating near the implant.

Giuseppe Carluccio^1,2 and Christopher Michael Collins^1,2
1Radiology, Center for Advanced Imaging Innovation and Research (CAI2R), New York, NY, United States, ²Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York, NY, United States

In a patient exam, SAR may cause temperature increase potentially leading to tissue damage or thermoregulatory distress. Hence, development of fast and accurate temperature computation methods could be useful for safety assurance. We propose a method considering more factors than ever before (including SAR, respiration, perspiration, convection, conduction, and local perfusion rates), where the temperature over an entire MRI exam is rapidly estimated exploiting the linearity of the bioheat equation. Nonlinear effects due to thermoregulatory mechanisms of the human body, such as the variation of local blood perfusion rate, are approximated with a fast spatial filter.

Elena Lucano^1,2, Micaela Liberti², Gonzalo G Mendoza¹, Tom Lloyd³, Francesca Apollonio², Steve Wedan³, Wolfgang Kainz¹, 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, Univerisity of Rome "Sapienza", Rome, Italy, ³Imricor Medical Systems, Burnsville, MN, United States

We aim to generate a quantitative method for RF-safety of patients with partially implanted leads at 64 MHz. Within this aim, the position of the RF feeding sources and the orientation of the polarization is often unknown, as it is the quantitative effect of such variables on the induced currents on the leads. The Electric field profile was studied by means of simulations and measurements with a coil loaded with a phantom, and simulations with an anatomical human model. Changes of up to 40% of E-field magnitude were observed. Future work is needed to develop a systematic exposure procedure.

Tilman Schubert^1,2, Utaroh Motosugi³, Diego Hernando¹, Camilo A Campo¹, Samir Sharma⁴, Scott Reeder^1,4,5,6,7, and Shane Wells^1
1Radiology, University of Wisconsin Madison, Madison, WI, United States, ²Clinic for Radiology and Nuclear Medicine, Basel University Hospital, Basel, Switzerland, ³Department of Radiology, University of Yamanashi, Yamanashi, Japan, ⁴Medical Physics, University of Wisconsin Madison, Madison, WI, United States, ⁵Biomedical Engineering, University of Wisconsin Madison, Madison, WI, United States, ⁶Medicine, University of Wisconsin Madison, Madison, WI, United States, ⁷Emergency Medicine, University of Wisconsin Madison, Madison, WI, United States

Ferumoxytol has gained increasing interest as a negative MR-contrast agent due to its high r2* relaxivity. However, limited data is available about the temporal course of the biodistribution of ferumoxytol. This study evaluated the biodistribution of ferumoxytol in different tissue types using repeated MR-measurements until the 30th day after administration. Our longitudinal MRI-study demonstrated that tissues of the monocyte−macrophage system show different, dose dependent R2* peaks after ferumoxytol injection. These results could help to determine the optimal, tissue specific imaging delay after ferumoxytol administration. Tissues not containing monocytes/macrophages parallel the time course of ferumoxytol in the blood pool.

Shi Feng¹, Shiloh Sison², Jazmine Garcia³, Gabriel Mouchawar³, and Richard Williamson^3
1Hardware development, St. Jude Medical, Sylmar, CA, United States, ²St. Jude Medical, Sunnyvale, CA, United States, ³St. Jude Medical, Sylmar, CA, United States

Metallic leads of an implanted electronic device such as a pacemaker may behave as antennae in the strong radio frequency electromagnetic field of MRI. The induced current surrounding the electrodes may heat the local tissue. The MRI-induced tissue heating around the electrodes of a pacemaker have only been investigated for pacemakers employing a single lead. In this paper, we examine the MRI-induced temperature rise (TR) of the tip electrode(s) associated with a pacemaker system with two St. Jude Medical Tendril 2088 STS leads, and compare it to the single result. Both transfer function and in vitro temperature rise are investigated.