MRI Safety with Anal Plugs
Remove the butt plug before entering the MRI scanner—any metallic implant or foreign body must be screened for MRI safety classification (MRI unsafe, MRI conditional, or MRI safe) before imaging, and anorectal foreign bodies containing ferromagnetic materials pose serious risks of displacement, heating, and injury in the magnetic field. 1
Primary Safety Concerns
The fundamental issue is whether the device contains any metallic components that could interact with the MRI's powerful magnetic field:
- All metallic items must be removed from patients before MRI, including dental prostheses, jewelry, and clothing with zippers or buttons 1
- Ferromagnetic materials can become dangerous projectiles when exposed to static magnetic fields ranging from 0.147 to 4.7 T, with documented serious injuries including facial trauma from oxygen tanks becoming missiles 2, 3
- Thermal injuries can occur from radiofrequency heating of metallic objects during scanning, even with appropriate precautions 1, 4
MRI Safety Classification System
All implants and devices must be categorized before MRI exposure 1:
- "MRI unsafe" = absolute contraindication—never scan 1
- "MRI conditional" = relative contraindication requiring specific conditions (field strength limits, positioning requirements) 1
- "MRI safe" = no contraindication—can proceed 1
The specific type, location, and material composition must be verified through manufacturer documentation or online resources (such as mrisafety.com) before scheduling 1
Practical Approach
Pre-Screening Protocol
- Use a standardized checklist to screen for implants, ports, catheters, metallic implants, vascular stents, coils, active implants, cardiac pacemakers, and any foreign bodies 1
- Obtain plain radiographs (anteroposterior and lateral views of chest, abdomen, and pelvis) if there is any suspicion of retained foreign bodies to identify position, shape, size, and material before proceeding 1
- Digital examination should occur AFTER imaging when foreign bodies are suspected, to prevent accidental injury to the examiner from sharp metallic objects 1, 5
Material Considerations
Most commercially available anal plugs are made from:
- Silicone, rubber, or plastic = typically MRI safe (no ferromagnetic properties) 6
- Metal components (stainless steel, aluminum, or decorative elements) = require specific safety verification 6
- Unknown composition = must be removed as a precautionary measure 3, 7
Common Pitfalls to Avoid
- Never assume non-metallic appearance equals safety—some materials contain embedded metallic particles or components not visible externally 2, 3
- Do not rely solely on patient reporting—patients may not know the exact composition of devices 2, 7
- Avoid delaying removal until the scan room—screening must occur during the pre-MRI safety questionnaire phase 1
Clinical Decision Algorithm
- Ask directly about the presence of any anal device during the standardized MRI safety screening 1
- If present, determine material composition from manufacturer documentation 1
- If any metallic components exist, verify MRI safety classification with manufacturer 1
- If composition is unknown or unverifiable, the device must be removed before entering the MRI suite 3, 7
- If the device is confirmed MRI safe (non-ferromagnetic), imaging may proceed, though removal is still preferable to avoid potential artifacts 1
Additional Safety Considerations
Beyond magnetic field interactions, other risks include:
- Image artifacts from any implant can create signal voids and geometric distortions, potentially compromising diagnostic quality 1
- Patient discomfort during prolonged scanning (5-50 minutes depending on protocol) may be exacerbated by retained devices 1
- Emergency access concerns—if complications arise during scanning, the presence of a foreign body complicates rapid intervention 1, 3
The safest approach is removal before entering the MRI environment, regardless of material composition, to eliminate all potential risks and ensure optimal image quality. 1, 3, 7