Evaluation of RF Heating due to Various Implants during MR Procedures

Abstract

We evaluated radiofrequency (RF) heating of various implants embedded in a gel phantom during magnetic resonance (MR) procedures. We examined the dependence of RF heating on variation in speciˆc absorption rate (SAR) and angle between the implant and the static magneticˆeld (B 0 ) and on the displacement of the phantom in the irradiation coil using a 1.5-tesla MR system, and we compared the in‰uence of RF heating on the same implant using a 3.0T MR system.Our results support the occurrence of RF heating of implants made of non-magnetizing metal. We observed greater RF heating when the implant was set parallel to B 0 , embedded at a shallower depth, and placed at the center of the RF irradiation coil. We also conˆrmed that the rise in temperature was proportionate to the increase in SAR. We considered the diŠerence in temperature elevation on depth of embedding to re‰ect the skin-depth eŠect of RF intensity for both the 1.5-and 3.0-T MR systems.

Low dose of continuous – wave microwave irradiation did not cause temperature increase in muscles tissue adjacent to titanium alloy implants – an animal study

“…RF heating of cobalt-chromium alloy implants and titanium alloy implants was evaluated in vitro by Muranaka. The maximum temperature rise of titanium implant was lower compared with cobalt-chromium [33,39]. Our results indicate that, under lower dose microwave irradiation (20 w-40 w), the temperature increase of muscles adjacent to titanium alloy implants was lower than 43°C.…”

“…In the case of implants with thin or sharp edges, electromagnetic field lines are focused along the edge or an end, leading to a high local flux [33], resulting in significant increase in absorption and temperature in tissues. In this study, no significant difference in temperature rise was observed between the ends and the middle part of the implants, due to the small size and good thermal conductivity of the implant.…”

“…It has a lower magnetic permeability and electric conductivity than common magnetic materials, and consequently less absorption of radio frequency (RF) [32]. The findings from studies in vitro indicated that the temperature changes of titanium and titanium alloys in RF electromagnetic field were lower compared with other metallic implants [27,33]. In fact, the safety of shortwave diathermy has been proven in clinical case reports.…”

Effects of Low-Dose Microwave on Healing of Fractures with Titanium Alloy Internal Fixation: An Experimental Study in a Rabbit Model

“…RF heating of cobalt-chromium alloy implants and titanium alloy implants was evaluated in vitro by Muranaka. The maximum temperature rise for titanium implant was obviously lower than that for cobalt-chromium [35,40]. Hence, the current study was based on the assumption that there is no dramatic temperature raise in tissues around titanium alloy implants resulting from a low dose microwave exposure.…”

Functionality of Veterinary Identification Microchips Following Low‐ (0.5 Tesla) and High‐field (3 Tesla) Magnetic Resonance Imaging

“…The degree of thermal effects in MRI depends on numerous factors, such as the magnetic properties of the metal, size and shape of the metallic body, the position of the body relative to the static magnetic field (B 0 ), and specific absorption rate (SAR). Latter in turn differs between MR field‐strengths . In a number of studies it was shown that the local temperature rise can exceed 5°C .…”