Is a covert metal Common Bile Duct (CBD) stent compatible with Magnetic Resonance Imaging (MRI) in an adult patient with a history of biliary obstruction or other conditions requiring stenting?

MRI Compatibility of Covered Metal CBD Stents

Covered metal biliary stents are generally MRI-compatible and safe for imaging, though they produce susceptibility artifacts that may affect image quality and target delineation, with the magnitude of artifacts depending on stent material composition.

Material-Specific MRI Safety Profile

The MRI compatibility of covered metal CBD stents varies significantly by material composition:

• Nitinol stents (the most common material for covered biliary stents) produce minimal to moderate susceptibility artifacts, with decreased T2* signal extending up to 5.1 mm at 1.5T and 8.5 mm at 3T from the stent edge 1

• Platinum-cored nitinol stents demonstrate similar artifact profiles to pure nitinol, with artifacts remaining within acceptable limits for diagnostic imaging 1

• Stainless steel stents produce the largest susceptibility artifacts and should be avoided when future MRI imaging is anticipated 1

• Polyethylene stents show no MRI artifacts but are not typically used as covered metal stents 1

Clinical Implications for Imaging

The artifacts produced by covered metal biliary stents have practical consequences:

• Susceptibility artifacts dominate over gradient-induced and RF-induced artifacts in all metal stent types 1

• For sequences with higher bandwidth per voxel (>275 Hz/voxel at 1.5T; >500 Hz/voxel at 3T), B0-related susceptibility artifacts become negligible (<0.2 voxels) 1

• In vivo studies demonstrate that changes in B0 and T2* induced by the stent exceed typical anatomical variations when the stent is positioned at 30° or greater angle to the main magnetic field 1

Safety Considerations

All modern covered metal biliary stents (nitinol and platinum-cored nitinol) are considered MR-conditional and safe for scanning at standard field strengths (1.5T and 3T). 1

Key Caveats:

• While safe for the patient, image quality degradation may limit diagnostic utility in the immediate stent vicinity 1

• If radiotherapy planning is anticipated, additional safety margins (5-8 mm) should be incorporated to ensure adequate target coverage due to artifact-induced uncertainty 1

• The specific stent manufacturer's MRI safety information should always be verified, as individual product specifications may vary

Practical Recommendations

When MRI imaging is needed in patients with covered metal CBD stents:

• Proceed with MRI without hesitation for standard diagnostic purposes, as these stents are MR-conditional 1

• Use sequences with higher bandwidth per voxel to minimize susceptibility artifacts 1

• Expect artifact-related signal loss within approximately 5-8 mm of the stent at 3T 1

• Document stent material type (preferably nitinol or platinum-cored nitinol) to predict artifact magnitude 1