Assessing RF heating of deep brain stimulation implants in high-field open-bore MRI systems

There is a steady growth in the use of implantable electronic devices for therapeutic applications in the U.S. and globally. The neurostimulation devices market was valued at $3.68 billion in 2015, with the fastest annual growth in deep brain stimulators (DBS) at 12.7%. This rapid increase in clinical applications of DBS parallels the large availability and need for magnetic resonance imaging (MRI). About 80% of patients with an implanted neurostimulation device will require an MRI within five years of implantation, but safety concerns due to RF heating of implants prevent most such patients from receiving these scans. Although there are few MR-conditional DBS devices available, they require restrictive imaging conditions that have proven hard to implement. This limitation has led almost two-third of hospitals to refrain from performing MRI on patients with DBS implants. The current MR labeling of DBS devices, as well as all MRI studies on the radiofrequency heating of conductive implants has been limited to horizontal (closed-bore) MRI systems. No literature exists on the safety of DBS imaging in vertical MRI scanners, which generate a fundamentally different electric and magnetic field distribution and are now available at 1.2 T field strength capable of high-resolution structural and functional studies. To make MRI accessible to patients with DBS devices, the proposed experiments will test the hypothesis that vertical MRI systems with a 90° rotated radiofrequency field orientation generate substantially less heating and image artifact around leads of DBS devices with realistic clinical configurations. In preliminary studies, a commercially available vertical coil (Oasis, Hitachi) generated 20-fold less local specific absorption rate of energy deposition at the tips of DBS leads in four patient-derived realistic models of isolated leads and fully implanted DBS systems compared to the standard birdcage body coil. These results, if verified in larger patient cohort