Letter: Unforeseen Hurdles Associated With Magnetic Resonance Imaging in Patients With Deep Brain Stimulation Devices.

Abstract

To the Editor: Modern deep brain stimulation (DBS) devices are often advertized as being “whole-body conditional,” and this label is an important consideration when assessing the suitability of DBS for a given patient (eg, a patient who would likely require spinal imaging in the future). However, we found that unforeseen contradictions between DBS vendor guidelines and MRI manufacturer manuals rendered diagnostic “whole-body” (eg, spine) imaging unfeasible at our center, leading to deleterious effects on patient care. As described previously,1 the main risk of MRI on deep DBS patients is heating at the DBS lead tips. To mitigate this risk, DBS vendor guidelines typically include 2 heating-related thresholds that scans must be acquired within: most commonly (1) specific absorption rate (SAR) or, if available, (2) B1 + rms. Of the 2, SAR thresholds are extremely restrictive while the more permissive B1 + rms metric is less established and not universally available. Although these factors have been useful in preventing adverse events, they also have limited MRI for DBS patients.2 At our institution, our previous MRI (1.5T GE-Signa; software: HDxT 23.0_V021406.a) did not offer B1 + rms, and the SAR thresholds specified in DBS vendor guidelines meant that it was only practical to acquire diagnostic quality imaging of the head. Given the demand for MRI in DBS patients—1 study estimating that up to 75% of patients require MRI within 10 years of DBS surgery, the majority (62%) of whom calling for body and/or spine scans3—we performed rigorous phantom testing to ensure the safety of off-label (ie, outside SAR threshold) spinal scans on our GE machine.4 Recently, we upgraded our MRI to the one enabling B1 + rms measurements (1.5T Siemens-Magnetom; software: XA20), theoretically allowing us to leverage a more permissive heating-related threshold and acquire diagnostic scans within DBS guidelines. However, we found that the Siemens system displayed a warning prohibiting scans based on B1 rms values: “The actual B1 rms value may be much higher than the value displayed. Do not scan patients with implants based on this value.” This is in conflict with the recommendations of DBS vendor guidelines, which even acknowledge potential discrepancies between real and predicted B1 + rms: “The actual B1 + rms value may differ slightly from the predicted value… The MRI Guidelines for Medtronic …requires only that the predicted B1 + rms value for the protocol is <2.0 µT.”5 Consequently, our MRI department was unable to perform clinically practical scans for extracranial pathology (eg, for the spine) without breaching DBS vendor guidelines or MRI manufacturer recommendations. The delays caused by this impasse have compromised patient care and ultimately led us back to square 1, in which we had to reproduce our phantom safety experiments using the Siemens MRI to facilitate off-label whole-body imaging. It is important that the DBS and radiology community are aware of the contradictory guidelines set by major MRI and DBS manufacturers, which we have not previously seen described in the literature and the considerable hurdles that they can impose.