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

Abstract

Purpose Patients with active implants such as deep brain stimulation (DBS) devices are often denied access to MRI due to safety concerns associated with the radiofrequency (RF) heating of their electrodes. The majority of studies on RF heating of conductive implants have been performed in horizontal close‐bore MRI scanners. Vertical MRI scanners which have a 90° rotated transmit coil generate fundamentally different electric and magnetic field distributions, yet very little is known about RF heating of implants in this class of scanners. We performed numerical simulations as well as phantom experiments to compare RF heating of DBS implants in a 1.2T vertical scanner (OASIS, Hitachi) compared to a 1.5T horizontal scanner (Aera, Siemens). Methods Simulations were performed on 90 lead models created from post‐operative CT images of patients with DBS implants. Experiments were performed with wires and commercial DBS devices implanted in an anthropomorphic phantom. Results We found significant reduction of 0.1 g‐averaged specific absorption rate (30‐fold, P < 1 × 10−5) and RF heating (9‐fold, P < .026) in the 1.2T vertical scanner compared to the 1.5T conventional scanner. Conclusion Vertical MRI scanners appear to generate lower RF heating around DBS leads, providing potentially heightened safety or the flexibility to use sequences with higher power levels than on conventional systems.

Modifying the trajectory of epicardial leads can substantially reduce MRI-induced RF heating in pediatric patients with a cardiac implantable electronic device

“…In contrast, there is a much larger degree of freedom in placing epicardial leads, giving rise to patient-to-patient variation in epicardial lead trajectories. As the magnitude and phase of the tangential component of MRI incident electric field along a lead's trajectory are shown to be indicators of lead's RF heating (13,14,(17)(18)(19), one would expect to see a large variation in RF heating of epicardial leads; conversely, new opportunities to increase patient safety through surgical modification of lead trajectories.…”

“…The strength of this coupling depends, among other factors, on the relative orientation of the lead with respect to the transmit electric field (E). As such, the trajectory of an implanted lead substantially affects its MR-induced RF heating (10)(11)(12)(13)(14)(15). This has important ramifications for patient safety as surgical guidelines are silent about how to position the excessive length of implanted leads within the body.…”

A workflow for predicting temperature increase at the electrical contacts of deep brain stimulation electrodes undergoing MRI

“…Various approaches have been proposed for predicting the temperature increase at the tip of metallic implants. For example, full‐wave electromagnetic (EM) simulations have been performed using the model of the RF coil, the electrode, and realistic human models 9–15 . Although this approach is valuable for gaining insight into different factors that affect the heating (e.g., electrode trajectory, the effect of implantable pulse generator [IPG]), it usually requires high computational power and expertise.…”

“…For example, full-wave electromagnetic (EM) simulations have been performed using the model of the RF coil, the electrode, and realistic human models. [9][10][11][12][13][14][15] Although this approach is valuable for gaining insight into different factors that affect the heating (e.g., electrode trajectory, the effect of implantable pulse generator [IPG]), it usually requires high computational power and expertise. Even with the availability of both, it is still challenging and time consuming to simulate the full model of a DBS electrode because of the complexity of the conductor geometry and the fine mesh size (∼microns) required.…”

A comparative study of MRI-induced RF heating in pediatric and adult populations with epicardial and endocardial implantable electronic devices

“…Tissue heating from radiofrequency (RF) excitation fields, however, remains a major issue. This "antenna effect" happens when the electric field of the MRI transmit coil couples with an elongated conductive lead, causing the specific absorption rate (SAR) of the RF energy to amplify at the lead's tip [8][9][10]. Consequently, patients with such leads are either contraindicated to receive MRI, or only approved to undergo MRI under strictly controlled conditions.…”