Study design, materials and methods
We prospectively recruited InterstimTM II model implanted patients requiring lumbar/spine or pelvis 1.5 T MRI. Patients completed validated questionnaires and a survey regarding their usual SNM sensation pre MRI scan. The implantable pulse generator (IPG) was interrogated and impedances and battery life were assessed pre and post MRI. Patients were monitored during MRI study. An MRI-related adverse events questionnaire was completed post MRI. Validated questionnaires were completed 1 month after the MRI to assess for any changes in SNM therapeutic efficacy. Descriptive statistics were calculated.
Interpretation of results
In this study, we found that no subjects with implanted SNM devices had any significant adverse events from undergoing 1.5 T lumbar MRI. Additionally, SNM therapeutic efficacy did not change 1 month post-MRI. A main safety concern of SNM with MRI is device heating during scanning due to transmitted radiofrequency power. Utilizing a phantom model, Quirouet et. al. demonstrated the risk of device heating is very low for lumbosacral 1.5 T MRI with an intact SNM system or with a fractured lead . We utilized multiple instruments to measure safety and therapeutic efficacy before and after. SNM devices were switched off before undergoing MRI, patients were periodically interviewed throughout the scan and none terminated the scan due to intolerance. No patients verbalized any sensation of heating during the MRI scan. However, when prompted about symptoms after the scan, 2 patients recalled a warm sensation and 1 patient reported mild discomfort near the IPG during the MRI. Otherwise, following the scan, no patients reported pain or discomfort.
As a number of patients undergo SNM explantation to facilitate MRI, it is important to recognize that many patients explanted do not pursue SNM re-implantation. As shown recently by Lloyd et al., only 10% of explanted patients pursued subsequent re-implantation . Therefore, the results of our study have the potential to improve device management surrounding MRI by establishing evidence of the ability to perform MRI near implanted SNM devices. Furthermore, our findings can translate into improved healthcare efficiency and reduced costs, by, providing a basis for reducing device explants to accommodate MRI, as well as enabling the implantation of devices in appropriate patients who know they may require future MRI studies.