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 cohorts and validated experimentally, will open the door to a plethora of structural and functional MRI applications to guide DBS therapy. The proposed experiments will develop a virtual family of patient body models (five tissue classes) implanted with DBS devices, perform numerical simulations to calculate radiofrequency heating during MRI in 1.2 T vertical systems (unlabeled) and compare to horizontal systems at 1.5 T (labeled) at different imaging landmarks, verify simulation results using anthropomorphic phantoms, and use verified computational models to develop lookup tables to select imaging parameters that constraint RF heating to less than what happens in a fever (1-3C). Completion of this work will provide, for the first time, a quantitative measure of temperature rise in tissue during MRI of patients with implanted leads in high-field open-bore MRI systems. Open bore MRI was developed to facilitate interventional applications, offering an ideal platform for MR-guided neurosurgery with potentially revolutionizing impact on DBS therapy. The resulting knowledge should also translate to patients with other types of implants, particularly those with intracranial EEG electrode grids, spinal cord stimulators, and electronic cardiac devices.
This project aims to develop computational methodologies that assess, for the first time, the heating of tissue during magnetic resonance imaging of patients with deep brain stimulation devices inside the new generation of high-field open-bore vertical MRI scanners. Results will produce data that will help to determine the safe range of imaging parameters and optimize clinical protocols and will support the development of standards and imaging guidelines that bring MRI accessible to these patients.
