In vitro investigation of pacemaker lead heating induced by magnetic resonance imaging: Role of implant geometry

Abstract

Purpose:To evaluate the effect of the geometry of implantable pacemakers (PMs) on lead heating induced by magnetic resonance imaging (MRI). Materials and Methods:In vitro experiments were conducted with two different setups, using fluoroptic probes to measure the temperature increase. The first experiment consisted of a rectangular box filled with a gelled saline and a pacemaker with its leads. This box was exposed in an MRI birdcage coil to a sinusoidal 64-MHz field with a calibrated whole-body specific absorption rate (WB-SAR) of 1 W/kg. The highest SAR and temperature increase (3000 W/kg, 12°C) occurred for the implant configuration having the largest area. The second experimental setup consisted of a human-shaped torso filled with gelled saline. In this setup the PM and its lead were exposed to a real MRI scanner, using clinical sequences with WB-SAR up to 2 W/kg. Results:We found that higher heating occurs for configurations with longer exposed lead lengths and that right chest PMs showed the highest temperature and local SAR (11.9°C, 2345 W/kg), whereas the left chest PMs were less heated (6.3°C, 1362 W/kg). Implant geometry, exposed lead length, and lead area must be considered in the wide variation of temperature increases induced by MRI. Conclusions:The amount of MRI-induced lead tip heating depends strongly on implant geometry, particularly the lead area, exposed lead length, and position of the implant in the phantom. Critical lead tip heating was found for the longer leads. Therefore, to minimize MRI-induced lead tip heating, the PM lead should be as short as possible.

Role of the lead structure in MRI‐induced heating: In vitro measurements on 30 commercial pacemaker/defibrillator leads

“…The WB-SAR of 1 W/ kg adopted during the heating tests is a typical value of clinical RF sequences for the MRI scanning, considering that the threshold of 2 W/kg is the maximum value allowed by the normal operating mode defined in IEC 60601-2-33. Given the 1 W/kg exposure, the temperature increases and SAR values obtained are consistent with the findings of previous studies (17,18,23).…”

“…The system is installed at the Department of Technology and Health of the Italian National Institute of Health and has been specially designed to provide a controlled exposure for MRI safety testing with regards to the RF field. Systems with the same features have been widely used in previous published studies (17,(22)(23)(24). It has also been demonstrated that, given the same implant configuration and the same WB-SAR delivered to the phantom, the induced heating inside the isolated birdcage coil is comparable with the one obtained in an actual MRI system using clinical MRI sequences (23).…”

“…Systems with the same features have been widely used in previous published studies (17,(22)(23)(24). It has also been demonstrated that, given the same implant configuration and the same WB-SAR delivered to the phantom, the induced heating inside the isolated birdcage coil is comparable with the one obtained in an actual MRI system using clinical MRI sequences (23). In addition, the use of an apparatus that reproduces the RF field of an MR system is mentioned among the methods described in the American Society for Testing and Materials (ASTM) F2182-09 standard (25).…”

“…The simulator consists of a torso-shaped transparent PVC phantom of the size of a 70 kg male and of an internal volume of about 30 L. The leads were fixed on a PVC grid placed inside the phantom. The use of human-shaped phantoms, even if not prescribed by technical standards, has been already used to complement measurements obtained with standardized phantoms (17,23). It has been demonstrated that the geometry of the phantom can affect the amount of the induced heating at the implant tip (17).…”

Magnetic Resonance Imaging and Implantable Devices

“…Metallic devices and leads can act as an antenna thus amplifying local radiofrequency energy deposition. [8][9][10] Fractured leads or lead loop configurations may increase the potential for heating. Epicardial leads that are not cooled by blood flow 11 and abandoned leads may also be prone to increased heating.…”