Objective: To characterize the RF-induced heating profile of the St. Jude Infinity lead within an IMRIS using a configuration that emulates intraoperative functional MRI during stimulation through a temporarily externalized DBS lead.

Background: Functional MRI is a powerful tool with the potential to further reveal the mechanistic underpinnings of both the efficacy and side-effects of DBS. Unfortunately, MRI-related RF-induced heating remains a major safety concern and careful magnet-specific testing is necessary prior to clinical studies.

Method: Testing was conducted in accordance with ASTM standards using a 1.5T Siemens Espree (Erlangen, Germany) integrated IMRIS (Winnipeg, Manitoba, Canada) with a TxRx head coil. The leads (model 1331) were secured within a polyacrylic, gel-filled container that approximated a patient’s head and torso, which was oriented to emulate surgical positioning. Two lead configurations were evaluated (straight versus looped), with three fluoroptic sensors (model m3300, Luxtron, CA, USA) used to record temperature. Four sequences were used: 1) 3-plane scout localizer; 2) Transverse Fast Low Angle Shot (FLASH); 3) Coronal T2-weighted TSE; and 4) 2d GE EPI. The T2 served as a high-RF control and was not intended for patient use. During the EPI, the lead’s proximal end was connected via a long, shielded cable to a copper Faraday cage in the control room. There, an Infinity IPG, gated by a scanner-triggered, custom Arduino-based device was used to deliver stimulation (0.5 or 4.0mA; 90 µs, & 130 Hz).

Results: Figure 1 [Figure 1] shows temperature changes recorded for the EPI and T2 sequences. As anticipated, the RF-intense T2 (head exposure: 1.3 W/kg) resulted in a marked temperature rise (> 5 deg. C), while the low-powered (0.1 W/kg) yielded no discernible temperature change under any condition (i.e., lead configurations or DBS amplitude).

Conclusion: Each sequence intended for use during in vivo scanning showed minimal temperature changes (<1 deg C), supporting the safety of those sequences under the under the strict configurations applied. These data represent a significant step for advancing future intraoperative studies to characterize lead directionality on BOLD activity and further correlate those data with post-operative efficacy and side-effects.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-radiofrequency-rf-induced-heating-profile-of-an-externalized-directional-dbs-lead-using-functional-imaging-sequences-in-an-intraoperative-magnetic-resonance-imaging-suite-imris/