Safety of MRI-guided vascular interventions

Longer electrically conducting parts are needed for various instruments such as pacemakers, defibrillators, deep brain stimulators and interventional instruments. Magnetic resonance imaging in the presence of these instruments can be potentially harmful, due to resonance effects and heating of conducting wires. A review of the literature revealed that neither manufacturers of pacemakers and defibrillators nor the FDA consider these medical instruments to be MR-safe, despite the fact that there are some reports about MR scanning of pacemaker patients without critical incidents. MR-guided angiographic interventions require not only high quality real-time imaging, but also MR compatible and MR-safe instruments. Consequently, metallic guidewires as used for angiographic interventions were examined during in vitro experiments in the MR environment. Heating of guidewires > 70 degrees was reported during in vitro experiments. Our own in vivo experiments using commercially available metallic guidewires observed heating to up to 35 degrees at the guidewire tip, despite the cooling effect of blood flowing around the guidewire. Moreover, we saw the development of sparks at the end of the guidewire if it was bent inside of the MR scanner and touched to the animal. But it was not possible to reliably repeat these heating results. We conclude that longer metallic parts have to be avoided inside the MR scanner to guarantee patient safety. In order to exploit more sophisticated technologies such as active tip tracking, solutions without the need for conducting wires have to be further developed before interventional MR can safely move into the clinical setting.