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

Abstract

Patients with deep brain stimulation (DBS) implants are often denied access to magnetic resonance imaging (MRI) due to safety concerns associated with RF heating of implants. Although MR-conditional DBS devices are available, complying with manufacturer guidelines has proved to be difficult as pulse sequences that optimally visualize DBS target structures tend to have much higher specific absorption rate (SAR) of radiofrequency energy than current guidelines allow. The MR-labeling of DBS devices, as well as the majority of studies on RF heating of conductive implants have been limited to horizontal close-bore MRI scanners. Vertical MRI scanners, originally introduced as open low-field MRI systems, are now available at 1.2 T field strength, capable of high-resolution structural and functional imaging. No literature exists on DBS SAR in this class of scanners which have a 90 rotated transmit coil and thus, generate a fundamentally different electric and magnetic field distributions. Here we present a simulation study of RF heating in a cohort of forty patient-derived DBS lead models during MRI in a commercially available vertical openbore MRI system (1.2 T OASIS, Hitachi) and a standard horizontal 1.5 T birdcage coil. Simulations were performed at two major imaging landmarks representing head and chest imaging. We calculated the maximum of 0.1g-averaged SAR (0.1g-SARMax) around DBS lead tips when a B1 + = 4 T was generated on an axial plane passing through patients body. For head landmark, 0.1g-SARMax reached 220188 W/kg in the 1.5 T birdcage coil, but only 1411 W/kg in the OASIS coil. For chest landmark, 0.1g-SARMax was 2417 W/kg in the 1.5 T birdcage coil and 32 W/kg in the OASIS coil. A paired two-tail t-test revealed a significant reduction in SAR with a large effect-size during head MRI (p < 1.510-8 , Cohen's d = 1.5) as well as chest MRI (p < 6.510-10 , Cohen's d = 1.7) in 1.2 T Hitachi OASIS coil compared to a standard 1.5 T birdcage transmitter. Our findings suggest that open-bore vertical scanners may offer an untapped opportunity for MRI of patients with DBS implants.

Safety and image quality at 7T MRI for deep brain stimulation systems: Ex vivo study with lead-only and full-systems

“…As a result, researchers have resorted to application of MRI beyond the currently approved labeling of the device based on RF heating assessment through phantom experiments or numerical simulations. These studies, however, have focused on 1.2T, 1.5T and 3T scanners due to their clinical prevalence [ 10 , 58 – 62 ]. This work presents the first study of MRI safety in patients with DBS implants at 7T, and as such, provides a frame of reference to compare risks and benefits of ultra-high field MRI in this patient population.…”

Vertical open‐bore MRI scanners generate significantly less radiofrequency heating around implanted leads: A study of deep brain stimulation implants in 1.2T OASIS scanners versus 1.5T horizontal systems

“…In a preliminary simulation study with three simplified DBS lead models, we showed that a vertical butterfly coil generated 4‐ to 14‐fold lower SAR at tips of implanted leads compared to a horizontal birdcage coil 11 . Later, we extended the study to include 40 lead models based on images of patients with lead‐only DBS systems which confirmed a significant reduction in RF heating 12 . Here, we report results of an expanded study on 90 patient‐derived DBS lead models including both lead‐only and fully implanted systems.…”

“…11 Later, we extended the study to include 40 lead models based on images of patients with lead-only DBS systems which confirmed a significant reduction in RF heating. 12 Here, we report results of an expanded study on 90 patient-derived DBS lead models including both lead-only and fully implanted systems. New patients were recruited from a second DBS center to account for the surgeon-dependent variability in routing of DBS leads.…”

Intraoperative MR Imaging during Glioma Resection

“…cardiac pacemaker and electrode). [94][95][96][97][98][99][100] MR unsafe corresponds to materials that are dangerous in MR environments, such as surgical scissors and forceps. [101][102][103][104] Preventing eddy current-induced complications in the patient Consideration must be given to eddy currents, which are generated in nearby conductors, including the largest eddy current generated in an MR scanner, which is a shield panel placed inside the gradient coil, which is part of the MR scanner, and when there is ferrous, eddy current is not the only cause of heat generation but also there is so-called antenna effect and current inflow.…”