Who cannot undergo Magnetic Resonance Imaging (MRI)?

Contraindications to MRI (Magnetic Resonance Imaging)

Patients with cardiac pacemakers, implantable cardioverter-defibrillators (ICDs), and certain ferromagnetic metallic implants cannot undergo MRI due to risk of device malfunction, heating, and potential movement or dislodgment of metallic objects. 1

Absolute Contraindications

Implanted Electronic Devices

• Cardiac pacemakers and ICDs are the most common absolute contraindications, accounting for approximately 0.08% of referred patients 2
• These devices pose risks of lead heating (the major safety concern), inappropriate pacing, device reprogramming, and potential patient harm 3
• According to the FDA, there are currently no truly "MRI-safe" or "MRI-compatible" standard pacemakers or ICDs, though MRI-conditional devices now exist 1, 3
• Other implanted electrical devices are also contraindicated 4

Ferromagnetic Metallic Implants

• Aneurysm clips are an absolute contraindication due to risk of movement in vital neural structures 4
• Shrapnel or metallic foreign bodies in biologically sensitive areas (particularly near vital neural, vascular, or soft-tissue structures) account for 0.23% of contraindicated referrals 2, 5
• Ferromagnetic bullets and shrapnel, especially steel-containing projectiles, can rotate and move in response to magnetic torque 5
• Stainless-steel or non-titanium implants may preclude MRI, particularly when located near the area being imaged 1

Relative Contraindications

Patient-Related Factors

• Severe claustrophobia affects 3-7% of patients, with up to 37% experiencing moderate to severe anxiety that necessitates procedure termination in 5-10% of cases 6
• The lengthy scan time (45-60 minutes for MRI versus 3-5 minutes for CT) significantly exacerbates claustrophobic symptoms 1, 6
• First-trimester pregnancy is considered a relative contraindication, accounting for 0.03% of referred patients 2

Contrast-Related Issues

• Severe allergy to gadolinium contrast agents prevents contrast-enhanced MRI 1
• Renal insufficiency or compromised renal function contraindicates gadolinium administration due to nephrotoxicity risk 1

Implants Generally Safe for MRI

The following are NOT contraindications and can safely undergo MRI:

• Coronary artery stents 3
• Prosthetic cardiac valves 3
• Metal sternal sutures 3
• Mediastinal vascular clips 3
• Epicardial pacing wires 3
• Most orthopedic devices and surgical hardware 4
• Tantalum mesh, surgical wire, skin staples, and most surgical clips 4

Important Clinical Considerations

Pre-Screening Requirements

• Rigorous screening is essential as 0.41% of all referred patients have absolute contraindications despite well-known recommendations 2
• Institutions placing implants should provide documentation to patients and physicians regarding MRI compatibility 2

Managing Claustrophobia

• Oral benzodiazepines (alprazolam 0.25-0.5 mg or intranasal midazolam 1-2 mg) are first-line anxiolytics for claustrophobic patients 6
• Screen for benzodiazepine contraindications including respiratory depression and alcohol use 6
• Ensure patients have transportation home and monitor for excessive sedation 6
• Consider large-bore MRI machines before resorting to open MRI systems 6

Artifact Considerations

• Metal implants create varying degrees of artifact depending on composition, mass, orientation, and position 4
• Ferromagnetic implants (particularly certain ACL reconstruction screws) can cause extensive signal loss and non-interpretable images 7
• Calcification detection remains problematic with MRI 1