Magnetic resonance imaging with implanted neurostimulators: An in vitro and in vivo study

OBJECTIVE: The goal was to assess the safety of magnetic resonance imaging (MRI) with implanted neurostimulators, in an in vitro and in vivo study. METHODS: Two different implantable pulse generators (IPGs) (ITREL II and 3; Medtronic, Minneapolis, MN) and different leads (separately and connected to an IPC) were tested in three different MRI scanners (0.2, 0.25, and 1.5 T). Measurements of the induced voltages (using an external oscilloscope) a nd the induced heat (using an infrared camera) were performed in an in vitr o study. Finally, 38 patients with implanted neurostimulator systems (leads and IPGs) underwent MRI in 50 examinations, with continuous monitoring by a physician with uninterrupted visual and vocal contact with the patient. T wenty-five patients were studied prospectively, with documented printouts o f the parameter settings before and after MRI. RESULTS: An induced voltage of 2.4 to 5.5 V was measured in the experimenta l configuration with a lead connected to an IPC. The voltage was higher wit h the leads alone, compared with the leads connected to the IPG, and was de pendent on the MRI scanner, the sequences, and the type of lead. No heat in duction was observed in any part of the hardware. No change of pulse shape or change of IPC parameters was observed during MRI. No adverse effects occ urred in patients with chronically implanted deep brain leads connected to an IPC. CONCLUSION: MRI can be safely performed in patients with implanted neurosti mulation systems with the tested deep brain leads connected to an IPC (ITRE L II and 3), with running parameters. No heat induction was detected, and t he experimentally measured induced voltage did not seem to harm the patient s. Only the reed switch of the IPGs was activated; the other parameters rem ained unchanged. Further investigations must be performed to study the loca l electrical effects in larger plate electrodes; these effects might cause slight discomfort. There is no danger with any type of electrode during MRI examinations if the electrodes lie outside the region of interest. These o bservations are restricted to the tested devices. A conscientious estimatio n of the risks and benefits of MRI for patients with implanted devices is r ecommended. If the type of device is not known to the examiner, MRI should still be considered to be contraindicated.