Browsing by Subject "Implant heating"

Now showing 1 - 4 of 4

Open Access
Reduction of implant RF heating through modification of transmit coil electric field
(WILEY, 2010-12-08) Eryaman, Y.; Akin, B.; Atalar, Ergin
In this work, we demonstrate the possibility to modify the electric-field distribution of a radio frequency (RF) coil to generate electric field-free zones in the body without significantly altering the transmit sensitivity. Because implant heating is directly related to the electric-field distribution, implant-friendly RF transmit coils can be obtained by this approach. We propose a linear birdcage transmit coil with a zero electric-field plane as an example of such implant-friendly coils. When the zero electric-field plane coincides with the implant position, implant heating is reduced, as we demonstrated by the phantom experiments. By feeding RF pulses with identical phases and shapes but different amplitudes to the two orthogonal ports of the coil, the position of the zero electric-field plane can also be adjusted. Although implant heating is reduced with this method, a linear birdcage coil results in a whole-volume average specific absorption rate that is twice that of a quadrature birdcage coil. To solve this issue, we propose alternative methods to design implant-friendly RF coils with optimized electromagnetic fields and reduced whole-volume average specific absorption rate. With these methods, the transmit field was modified to reduce RF heating of implants and obtain uniform transmit sensitivity.
Open Access
Reduction of the radiofrequency heating of metallic devices using a dual‐drive birdcage coil
(Wiley, 2013) Eryaman, Yiğitcan; Türk, Esra Abacı; Oto, C.; Algin, O.; Atalar, Ergin
In this work, it is demonstrated that a dual-drive birdcage coil can be used to reduce the radiofrequency heating of metallic devices during magnetic resonance imaging. By controlling the excitation currents of the two channels of a birdcage coil, the radiofrequency current that is induced near the lead tip could be set to zero. To monitor the current, the image artifacts near the lead tips were measured. The electric field distribution was controlled using a dual-drive birdcage coil. With this method, the lead currents and the lead tip temperatures were reduced substantially [<0.3°C for an applied 4.4 W/kg SAR compared to >4.9°C using quadrature excitation], as demonstrated by phantom and animal experiments. The homogeneity of the flip angle distribution was preserved, as shown by volunteer experiments. The normalized root-mean-square error of the flip angle distribution was less than 10% for all excitations. The average specific absorption rate increased as a trade-off for using different excitation patterns. Copyright © 2012 Wiley Periodicals, Inc.
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.
Open Access
A temperature sensor implant for active implantable medical devices for in vivo subacute heating tests under MRI
(John Wiley and Sons, 2018) Silemek, B.; Açıkel, V.; Oto, C.; Alipour, A.; Aykut, Z. G.; Algın, O.; Atalar, Ergin
Purpose: To introduce a temperature sensor implant (TSI) that mimics an active implantable medical device (AIMD) for animal testing of MRI heating. Computer simulations and phantom experiments poorly represent potential temperature increases. Animal experiments could be a better model, but heating experiments conducted immediately after the surgery suffer from alterations of the thermoregulatory and tissue properties during acute testing conditions. Therefore, the aim of this study was to introduce a temperature sensor implant that mimics an AIMD and capable of measuring the electrode temperature after implantation of the device without any further intervention at any time after the surgery in an animal model. Methods: A battery-operated TSI, which resembled an AIMD, was used to measure the lead temperature and impedance and the case temperature. The measured values were transmitted to an external computer via a low-power Bluetooth communication protocol. In addition to validation experiments on the phantom, a sheep experiment was conducted to test the feasibility of the system in subacute conditions. Results: The measurements had a maximum of 0.5°C difference compared to fiber-optic temperature probes. In vivo animal experiments demonstrated feasibility of the system. Conclusion: An active implant, which can measure its own temperature, was proposed to investigate implant heating during MRI examinations. Magn Reson Med 79:2824-2832, 2018.