Browsing by Author "Silemek, Berk"
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Item Open Access MR safety watchdog for active catheters: wireless impedance control with real‐time feedback(Wiley, 2020) Özen, A. Ç.; Silemek, Berk; Lottne, T.; Atalar, Ergin; Bock, M.Purpose: To dynamically minimize radiofrequency (RF)‐induced heating of an active catheter through an automatic change of the termination impedance. Methods: A prototype wireless module was designed that modifies the input impedance of an active catheter to keep the temperature rise during MRI below a threshold, ΔTmax. The wireless module (MR safety watchdog; MRsWD) measures the local temperature at the catheter tip using either a built‐in thermistor or external data from a fiber‐optical thermometer. It automatically changes the catheter input impedance until the temperature rise during MRI is minimized. If ΔTmax is exceeded, RF transmission is blocked by a feedback system. Results: The thermistor and fiber‐optical thermometer provided consistent temperature data in a phantom experiment. During MRI, the MRsWD was able to reduce the maximum temperature rise by 25% when operated in real‐time feedback mode. Conclusion: This study demonstrates the technical feasibility of an MRsWD as an alternative or complementary approach to reduce RF‐induced heating of active interventional devices. The automatic MRsWD can reduce heating using direct temperature measurements at the tip of the catheter. Given that temperature measurements are intrinsically slow, for a clinical implementation, a faster feedback parameter would be required such as the RF currents along the catheter or scattered electric fields at the tip.Item Open Access RF Safety of Active Implantable Medical Devices(John Wiley & Sons, Ltd. All rights reserved., 2019) Silemek, Berk; Açıkel, V.; Atalar, Ergin; Harris, R.K.; Wasylishen, R.L.The radiofrequency (RF) safety of active implantable medical devices (AIMDs) during an magnetic resonance imaging (MRI) scan is discussed in this article. The problem arises from the RF interaction of an AIMD with the MRI scanner is presented. The researchers simulated and modeled to understand the problem. They also developed techniques to resolve the RF safety problem by altering the design of AIMDs. Furthermore, implant friendly imaging solutions are developed. Validated the findings novel in vivo techniques. Clinical investigations are carried out to understand the extent of the problem. In this article, an incomplete summary of the investigations in this field is given.Item Open Access Wireless control of induced radiofrequency currents in active implantable medical devices during MRI(International Society for Magnetic Resonance in Medicine, 2020) Açıkel, V.; Silemek, Berk; Atalar, ErginPurpose To introduce a prototype active implantable medical device (AIMD) for which the induced radiofrequency currents can be controlled wirelessly. Methods The modified transmission line method is used to formulate how the lead‐case impedance of an AIMD affects the temperature rise around the electrode. A prototype AIMD is designed with the aim of controlling the unwanted temperature rise around its electrode during an MRI examination by altering the impedance between the lead and the case of the implant. MRI experiments were conducted with this prototype implant, which also has a built‐in temperature sensor at its electrode. During the experiment, the implant’s lead‐case impedance was controlled using Bluetooth communication with a remote computer, and the lead tip temperature was recorded. Results Ten different lead‐case impedance values and their corresponding tip temperature rises were examined during MRI experiments. The experimental results confirmed that the tip temperature rise can be controlled by varying the lead‐case impedance wirelessly. Conclusion The feedback from the temperature at the AIMD tip, together with variable lead‐case impedance, enables control of the safety profile of the AIMD during an MRI examination.