MRI T-R Coil Placement for Brain MRI in Patients with Sacral Nerve Stimulators
For brain MRI in a patient with a sacral nerve stimulator, the MRI technician should position the standard head T-R coil normally around the patient's head, ensuring the implanted pulse generator (IPG) remains outside the MRI isocenter and following manufacturer-specific MRI conditional labeling for the device.
Pre-Scan Device Management
Before coil placement, critical preparatory steps must be completed:
- The sacral nerve stimulator must be evaluated and deactivated by the implanting physician or trained personnel before entering the MR environment 1, 2, 3.
- Document all device parameters (stimulation amplitude, impedances) prior to deactivation to enable accurate reprogramming after the scan 2, 3.
- Verify the specific device model and its MRI conditional status with the manufacturer, as InterStim II devices are approved only for head MRI, while newer MRI-compatible InterStim models have broader scanning permissions 1, 4.
Coil Positioning Technique
The standard approach for head coil placement applies, with specific safety considerations:
- Position the patient's head in the center of the head T-R coil as you would for any brain MRI, ensuring proper anatomical coverage 1.
- The sacral nerve stimulator IPG (typically implanted in the upper buttock or lower abdomen) must remain well outside the MRI isocenter during brain imaging, which is naturally achieved with standard head positioning 2.
- Use transmit/receive coils rather than body coils when possible to minimize RF exposure to the implanted device 1.
Critical Safety Protocols
Several safety measures must be implemented during coil setup and scanning:
- Continuous patient monitoring is mandatory throughout the procedure, with the patient instructed to report any unusual sensations, pain, or discomfort immediately 2, 3.
- The RF exposure parameters must be strictly controlled according to manufacturer guidelines, as neurostimulators are susceptible to RF heating and gradient field interference 5.
- An MR Authorised Person (typically the supervising radiographer) maintains ultimate operational responsibility for safety during the procedure 5.
Post-Scan Device Verification
After completing the brain MRI:
- The device must be examined and reactivated by qualified personnel, with verification that all parameters match pre-scan settings 2, 3.
- Assess device function through patient feedback and impedance testing to ensure proper operation 3.
- Document any changes in device perception or function, though studies show brain MRI at 1.5T typically causes no functional changes when protocols are followed 2, 3.
Important Caveats
The presence of neurostimulators creates thermal injury risk from RF fields, which is why strict adherence to scanning parameters is essential 5. While older guidelines suggested patients with neurostimulators should not undergo MRI, manufacturer protocols now permit head MRI in many devices if specific safety guidelines are followed 5.
Device removal for MRI should be avoided whenever possible, as only 10% of patients who have devices explanted for imaging ultimately undergo reimplantation 6. This underscores the importance of following proper MRI conditional protocols rather than defaulting to device removal.