Sacral nerve neurostimulators are used to treat urinary retention, overactive bladder, and constipation. Medtronic produces these devices under the tradename InterStim®. Like a cardiac pacemaker, the InterStim system consists of a small titanium-encased pulse generator and battery implanted subcutaneously in the upper buttocks connected by a thin wire inserted through sacral foramen into the pelvis with terminal electrodes in the region of the S2-S4 sacral nerves.
- Horizontal bore 1.5T systems only
- Head MRI only using a transmit/receive head coil (no RF body coil transmission)
- Gradient slew rate limited to 200T/m/s
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Early model numbers contraindicated for MR imaging can be found in the Medtronic reference below. There is probably no risk to the patient, but MRI might make cause malfunction of the pulse generator. Knee imaging using a transmit-receive coil is not included as an allowed exception, but I would expect this restriction to be lifted in the future as it has for other similar devices.
Medtronic. MRI guidelines for InterStim therapy neurostimulation systems, 2012. (Always check manufacturer's web site for most recent version of this document and current recommendations)
Shellock F. MRISafety.com. (The essential resource providing MR safety information and links for over 5000 implanted devices
Can vagal nerve stimulators be safely scanned?