Screening High-Risk Implants & Foreign Bodies

Screening High-Risk Implants & Foreign Bodies

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Active Implantable Medical Devices

Active devices have a power source or electrical function. Risks include malfunction, unintended stimulation, lead-tip heating, displacement and therapy interruption. Identify the entire implanted system, not just the visible generator: manufacturer, model, leads, implantation date, revisions and abandoned components. Obtain current manufacturer instructions and the responsible team's clearance before controlled-zone entry.

Pacemakers and defibrillators

MR Conditional labeling applies to an approved system under specified conditions. A generator card does not establish that every lead is approved. The device team determines dependence, battery status, programming, monitoring and postscan checks. Some non-MR-conditional systems can undergo MRI through specialized clinical protocols after multidisciplinary review; they are not all automatically MR Unsafe. Abandoned, fractured or epicardial leads add complexity and potential heating risk and require escalation. The assistant neither declares these systems safe nor assumes that every such patient is permanently barred from all MRI.

Neurostimulators and implanted pumps

Deep brain, spinal cord and vagal stimulators have model-specific restrictions on field strength, coils, anatomy, RF exposure and device state. Some allow body-coil transmission; others do not. Verify all components and follow the exact labeling. Programming is performed by the appropriate trained team. Do not assume switching a device off removes heating risk.

Implanted pumps may have MR-conditional procedures and postscan checks. A temporary motor stall or therapy interruption can be clinically important, especially for intrathecal baclofen. Determine the product-specific plan and clinical support before scanning. Do not interrupt a critical infusion casually.

Cochlear implants and external devices

Cochlear-implant requirements vary: some require magnet removal or a specified splint/headwrap, while others permit scanning with the magnet retained without those measures. Identify the model rather than applying one headwrap rule to every recipient. Remove external sound processors as instructed. For wearable pumps and glucose monitors, obtain current labeling for the exact product; many must be removed, but recently approved exceptions exist. The clinical team plans alternative monitoring or therapy and replacement when removal is required.

Passive Metallic Implants: Risks, Torque, and Heating

Passive implants contain no internal electrical power source. Primary hazards involve mechanical displacement (translational force and rotational torque), thermal heating, and image artifacts.

Intracranial Aneurysm Clips

A ferromagnetic clip can experience dangerous displacement or torque near a cerebral vessel. Do not infer the material from a brand family or a year alone. An unknown clip requires investigation and must not be cleared by the assistant. Retrieve the exact manufacturer/model, operative evidence and current MR labeling for qualified review. A prior uneventful MRI does not by itself establish safety. If records remain unavailable, the responsible MR physician determines whether any further assessment is appropriate under the formal policy; the assistant does not improvise a test or clear entry.

Heart Valves and Annuloplasty Rings

Prosthetic heart valves (mechanical and bioprosthetic) and annuloplasty rings contain metallic structural rings. Extensive clinical testing has demonstrated that many prosthetic heart valves have MR Conditional labeling. The hydrodynamic anchoring force exerted by the contracting heart muscle and tissue endothelization far exceeds the magnetic forces exerted by a 1.5T or 3.0T field. However, relevant model and clearance information must still be documented in the clinical safety record.

Orthopedic Hardware

Total hip arthroplasties, total knee replacements, intramedullary rods, and spinal fusion screws are typically fabricated from titanium, cobalt-chromium, or austenitic surgical stainless steel. Once fibrous tissue integration or osseointegration occurs (depending on the procedure and patient), mechanical risk still requires evaluation under the labeling and local policy. The primary concerns are localized RF heating during long spine sequences and severe magnetic susceptibility artifacts that distort diagnostic anatomy.

Cutaneous Tattoos and Permanent Makeup

Dark cosmetic pigments and amateur tattoos frequently incorporate metallic salts, particularly ferrous iron oxides. The oscillating RF magnetic field induces circular eddy currents within the conductive pigment particles. Patients may experience tingling, stinging, or first- to second-degree cutaneous burns.

• Mitigation: Explain that unexpected warmth or pain must be reported immediately. Follow the MR safety team's plan for the tattoo and use only approved cooling aids; do not improvise wet conductive materials in contact with coils or cables.

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Investigating Possible Metallic Foreign Bodies

Ask about penetrating injuries, bullets, shrapnel and metal striking the eye. Occupational welding or grinding alone is not an automatic indication for orbital radiographs. Clarify whether there was a relevant injury, medical attention, possible globe penetration and documented removal. A prior uneventful MRI is not sufficient evidence that an orbital fragment is absent.

The 2026 ACR manual calls for orbital evaluation when there is a history of potentially ferromagnetic orbital trauma for which medical attention was sought, or otherwise high suspicion of globe penetration. Evaluation can use a single orbit radiograph with more views as needed, or a radiologist's assessment of adequate prior thin-section CT obtained after the event. Do not prescribe a universal Waters-plus-lateral series or promise a 0.1-mm detection threshold. The radiologist selects and interprets the study.

For fragments elsewhere, risk depends on composition, size, location near vulnerable structures, time since injury, possible fixation and RF exposure. Investigation precedes entry; a superficial fragment in muscle is not identical to a fragment near the eye or spinal cord. Ferromagnetic detection is an adjunct and cannot establish the absence or safety of every internal foreign body.

Screening Scenario

A patient brings a modern pacemaker card but reports an older retained lead. Pause the workflow, document the lead history and contact the technologist and device/safety team. Do not clear the patient from the generator card alone, and do not announce a permanent MRI ban. The complete system and clinical setting require assessment.