RF heating of deep brain stimulation implants in open‐bore vertical MRI systems: A simulation study with realistic device configurations

Abstract

Purpose Patients with deep brain stimulation (DBS) implants benefit highly from MRI, however, access to MRI is restricted for these patients because of safety hazards associated with RF heating of the implant. To date, all MRI studies on RF heating of medical implants have been performed in horizontal closed‐bore systems. Vertical MRI scanners have a fundamentally different distribution of electric and magnetic fields and are now available at 1.2T, capable of high‐resolution structural and functional MRI. This work presents the first simulation study of RF heating of DBS implants in high‐field vertical scanners. Methods We performed finite element electromagnetic simulations to calculate specific absorption rate (SAR) at tips of DBS leads during MRI in a commercially available 1.2T vertical coil compared to a 1.5T horizontal scanner. Both isolated leads and fully implanted systems were included. Results We found 10‐ to 30‐fold reduction in SAR implication at tips of isolated DBS leads, and up to 19‐fold SAR reduction at tips of leads in fully implanted systems in vertical coils compared to horizontal birdcage coils. Conclusions If confirmed in larger patient cohorts and verified experimentally, this result can open the door to plethora of structural and functional MRI applications to guide, interpret, and advance DBS therapy.

The effect of device configuration and patient’s body composition on image artifact and RF heating of deep brain stimulation devices during MRI at 1.5T and 3T

“…This oversimplified approach to MRI safety assessment is concerning for two reasons. First, as RF heating is highly sensitive to implant's configuration and its orientation with respect to MRI electric field (14)(15)(16)(17)(18)(19)(20)(21)(22), and as trajectory of DBS leads is substantially variant among patients (23), basing safety inferences on few tested configurations can expose a large number of patients to undue risk. Second, conclusions drawn from studies in single-material box-shaped phantoms may not apply to the realistic cases, as the distribution of electromagnetic fields depend upon the geometry and composition of the sample.…”

Effect of Device Configuration and Patient's Body Composition on the RF Heating and Nonsusceptibility Artifact of Deep Brain Stimulation Implants During MRI at 1.5T and 3T

“…Such off‐label studies have relied on in‐home safety assessments mostly performed in ASTM‐like phantoms (ie, the box‐shaped phantom filled with a single material), and with a limited number of DBS device configurations 14,15 . This oversimplified approach to MRI safety assessment is concerning for two reasons: First, RF heating is highly sensitive to the configuration of an implant and its orientation with respect to MRI electric field 10,16–20 . As trajectories of DBS leads are substantially variant among patients, basing safety inferences on a few tested configurations can expose a large number of patients to undue risk 21 .…”

RF heating of deep brain stimulation implants during MRI in 1.2 T vertical scanners versus 1.5 T horizontal systems: A simulation study with realistic lead configurations

“…As the orientation and phase of MRI incident electric field along the trajectory of an elongated implant has a substantial effect on the local SAR at the electrode tips [1,[3][4][5][6][7][8], we hypothesized that vertical scanners generate a statistically different RF heating compared to horizontal systems. Our hypothesis is based on a preliminary study of RF heating of DBS implants in three (3) realistic patient models which showed 4-to 14-fold reduction in the maximum local SAR around DBS electrodes in a vertical 1.2 T coil compared to a horizontal 1.5 T coil [2]. Here we extend our previous work to include a cohort of 20 patient models with bilateral DBS leads (40 lead models in total) with realistic trajectories.…”

“…Vertical scanners, originally introduced as low-field open-bore systems, are now available at high field strength capable of high-resolution structural and functional studies. No literature (except our recent work [2]) exists on RF heating of DBS implants inside this class of scanners which have a 90 rotated transmit coil and thus generate a fundamentally different distribution of electric and magnetic fields inside patient's body. As the orientation and phase of MRI incident electric field along the trajectory of an elongated implant has a substantial effect on the local SAR at the electrode tips [1,[3][4][5][6][7][8], we hypothesized that vertical scanners generate a statistically different RF heating compared to horizontal systems.…”