Phantom Safety Assessment of 3 Tesla Magnetic Resonance Imaging in Directional and Sensing Deep Brain Stimulation Devices

Abstract

INTRODUCTION MRI is both a crucial clinical and research tool for patients with deep brain stimulation (DBS) devices. However, safety concerns predominantly related to device heating have limited such imaging. Rigorous safety testing has demonstrated that scanning outside of vendor guidelines may be both safe and feasible, unlocking unique opportunities for advanced imaging in this patient population. Currently, however, 3T MRI safety data including advanced MRI sequences in novel directional and sensing DBS devices is lacking. METHODS An anthropomorphic phantom replicating bilateral DBS system was used to assess the temperature rise at the electrode tips, implantable pulse generator, and cranial loop during acquisition of routine clinical sequences (3D T1, GRE T2*, T2 FSE) and advanced imaging sequences including functional MRI (fMRI), arterial spin labelling (ASL) and diffusion weighted imaging (DWI). Measures of radiofrequency exposure specific absorption rate (SAR) and root-mean-square value of the MRI effective component of the RF transmission field (B1+rms) were also recorded as an indirect measure of heating. Testing involved both a new directional and sensing DBS device (Medtronic: B30015 leads and Percept PC neurostimulator) and a previous-generation DBS device (Medtronic: 3387 leads and Percept PC neurostimulator) in combination with a state-of-the-art (Siemens MAGNETOM Prisma) and a previous-generation (GE Signa HDxt) 3T MRI scanner. RESULTS On the state-of-the-art 3T MRI scanner, the new DBS device produced safe temperature rises with clinically used sequences and fMRI but not with other advanced sequences such as DWI and ASL, which also exceeded B1+rms vendor guidelines (i.e.≤2μT). When scanned on the previous MRI scanner, the recent DBS device produced overall lower and slower temperature rises compared to the previous DBS model. Among the sequences performed on this scanner, several (3D T1, DWI, T2 FSE, and ASL) exceeded the approved SAR vendor limit (<1W/kg), but only ASL resulted in an unacceptable temperature rise during scanning of the previous DBS model. CONCLUSION These phantom safety data show that both clinically-used MRI sequences and research sequences such as fMRI can be successfully acquired on 3T MRI scanners with a novel directional and sensing DBS model. As several of these sequences were obtained outside regulatory-approved vendor guidelines, pre-emptive safety testing should be done. As directional leads become increasingly common, improving MRI safety knowledge is crucial to expand clinical and research possibilities.