Is using a GE HDx head coil for MRI appropriate for a patient with a Medtronic InterStim sacral neurostimulator?

MRI Head Coil Use with Medtronic InterStim: Safety Assessment

Using a GE HDx head coil for MRI is appropriate for a patient with a Medtronic InterStim sacral neurostimulator, provided the device is MRI-conditional and proper safety protocols are followed, including turning off the device before scanning and ensuring the scan parameters remain within manufacturer specifications.

Device-Specific MRI Compatibility

The appropriateness depends critically on which InterStim model the patient has implanted:

Older InterStim Systems (Pre-2020)

• Only approved for 1.5T head scans as of 2012 1
• Head coil use is explicitly within labeled indications
• Body regions other than the head were historically contraindicated

Newer InterStim Systems (Post-August 2020)

• InterStim II and Micro devices with SureScan leads: Full-body MRI-conditional at both 1.5T and 3T 1
• Head scanning with appropriate coils is well within safety parameters
• Real-world data shows safety even for non-head body regions 2

Critical Safety Considerations for Head Coil Use

The head coil itself is appropriate because:

1. Anatomical distance: The head coil is positioned far from the sacral implant site, minimizing electromagnetic interference and RF heating risks 1

2. Lower risk profile: Head scans generate less concern than imaging near the device location 3

3. Clinical evidence: Multiple studies demonstrate safety of MRI in InterStim patients, with the vast majority of complications occurring only during body scans near the device 2, 3

Mandatory Pre-Scan Protocol

Before proceeding with any MRI (regardless of coil type):

• Verify device model and MRI-conditional status - this is non-negotiable 1, 4
• Turn device OFF before entering scanner 2, 3
• Check for contraindications: fractured leads, lead extenders, or abandoned leads 5
• Confirm scan parameters within manufacturer specifications:
  • Field strength (1.5T vs 3T compatibility)
  • Spatial gradient limits (typically 1000-4000 Gauss/cm) 6
  • Specific absorption rate (SAR) limits
  • Maximum scan time restrictions 6

Common Pitfalls to Avoid

Do not assume all InterStim devices have the same MRI compatibility - older models have significant restrictions 1. The metadata showing "GE HDx Head coil" tells you about the coil but reveals nothing about whether proper device interrogation occurred.

Surface coil interference: While head coils are generally safe, note that surface coils can interfere with some implanted sensors (though this applies to cardiac devices, not sacral neurostimulators) 5

Patient monitoring: Even for head scans, patients should be monitored during imaging and queried about sensations at the implant site 3. In one study, 2 of 191 MRI scans (1%) resulted in transient electrifying pain or heat at the implant site 2.

Post-Scan Requirements

• Reprogram device to previous therapeutic settings 3
• Verify device function: Check impedances and battery life 3
• Assess therapeutic efficacy at follow-up 3

Evidence Quality Note

The safety data comes primarily from observational studies rather than randomized trials, but consistently shows favorable safety profiles when manufacturer guidelines are followed 2, 3. The most robust study included 55 patients with 191 total MRI scans, finding only 2 transient complications (1%) 2.

The head coil is appropriate, but only if the underlying device compatibility and safety protocols are confirmed first. The coil type is less important than verifying the device model and following manufacturer-specific MRI conditions 1, 4.