MRI Safety with Cerebral Aneurysm Clips
Cerebral aneurysm clips are NOT an absolute contraindication for MRI, but require careful assessment of the specific clip model and material composition before proceeding with imaging. The critical distinction is between older ferromagnetic clips (unsafe) and modern non-ferromagnetic clips (safe), with the transition occurring around the year 2000 in most centers 1, 2.
Risk Assessment Framework
Primary Safety Concern
- The main hazard is movement or rotation of ferromagnetic clips due to the main magnetic field, which could dislodge the clip from the aneurysm and cause catastrophic hemorrhage 2.
- Four serious incidents involving aneurysm clips in MRI have been documented in incident databases, underscoring the real-world risk when ferromagnetic clips are exposed to MRI 2.
Known Clip Models
- If the clip model is documented and confirmed to be non-ferromagnetic (made from MP35N, Phynox, Elgiloy, or 316 LVM stainless steel), MRI at ≤3T is safe 3, 4, 5.
- Specific safe clip series include: Yasargil Phynox, Sugita Elgiloy, Vari-Angle McFadden (MP35N), and Yasargil 316 LVM stainless steel clips, which show no or minimal deflection in magnetic fields 4, 5.
- MP35N clips (including 155 different models tested) demonstrate acceptable safety profiles at 3T with minimal magnetic field interactions, temperature increases <1.8°C, and no risk of in situ movement 3.
Unknown Clip Models
- When the clip model cannot be determined from medical records, obtain standard skull x-rays in two planes and use online databases (such as ClipFinder) to identify the clip by comparing radiographic appearance 6.
- Seven specific aneurysm clip models from four different series have been identified as ferromagnetic and NOT MRI-compatible through deflection angle testing 6.
- In the Netherlands and many developed countries, no ferromagnetic clips have been implanted since 2000, providing a temporal cutoff for risk stratification 2.
Clinical Decision Algorithm
For Clips Implanted After 2000
- Proceed with MRI at ≤3T after confirming with the implanting institution that only non-ferromagnetic clips were used during that time period 2.
- Document the verification process in the medical record 2.
For Clips Implanted Before 2000
- Obtain skull x-rays and attempt clip identification using available databases before proceeding 2, 6.
- If identification confirms a non-ferromagnetic clip, proceed with MRI 6, 4.
- If the clip cannot be identified or is confirmed ferromagnetic, MRI is contraindicated—use alternative imaging such as CT angiography or catheter angiography 1.
For Follow-Up Imaging of Treated Aneurysms
- MRA at 3T is the preferred surveillance modality for patients with MRI-compatible clips, offering 95% sensitivity despite some clip-related artifacts 7, 8.
- Catheter angiography (DSA) remains the gold standard when clip artifacts limit MRA interpretation or when precise assessment of clip placement is required 7.
- CTA is limited by significant metallic streak artifacts from clips but can be used when MRI is contraindicated 7, 9.
Important Caveats
Artifact Considerations
- Even non-ferromagnetic clips create local image artifacts that may obscure the area immediately adjacent to the clip, potentially limiting diagnostic utility if the region of interest is near the clip 3, 4.
- Artifact reduction techniques are available to improve visualization of treated aneurysms and parent vessels 9.
Field Strength Limitations
- These safety recommendations apply specifically to 1.5T and 3T whole-body MRI systems with horizontal closed bore superconducting magnets, which represent the majority of clinical scanners 2.
- Higher field strengths require separate safety evaluation 2.
Documentation Requirements
- Care is required in patients with cerebrovascular clips as certain older models remain unsafe in the MR environment, and verification of clip type must be documented before proceeding 1.
- When in doubt about clip compatibility, choose alternative imaging methods to avoid catastrophic complications 1.