What are the contraindications for a patient undergoing a Magnetic Resonance Imaging (MRI) scan?

MRI Contraindications

The major contraindication to MRI is the presence of specific ferromagnetic and/or conducting implants such as cardiac pacemakers, although MRI can be performed safely in patients with pacemakers under rigorous safety conditions. 1

Absolute Contraindications

Ferromagnetic Implants and Devices

• Most electronic implants are absolute contraindications, as they become dangerous projectiles in the magnetic field and can cause severe tissue damage 2, 3
• Certain older cerebrovascular clips pose significant risk due to ferromagnetic properties 2
• Ferromagnetic foreign bodies, particularly intraorbital metallic fragments, are absolute contraindications 2
• Any endotracheal tube containing ferromagnetic wire reinforcement (such as standard flexometallic tubes with stainless steel wire spirals) must not be used in MRI 2

Device Classification System

• Devices classified as "MRI unsafe" represent absolute contraindications and cannot be scanned under any circumstances 3
• All implants must be evaluated according to MRI safety classification: MR Safe, MR Conditional, or MR Unsafe 2

Relative Contraindications

Cardiac Devices

• Pacemakers and implantable cardioverter-defibrillators are relative contraindications, though some newer models may be MR conditional 2
• When MRI is medically necessary in pacemaker patients, scanning can be performed under highly controlled conditions with device interrogation before and after, continuous monitoring, and full resuscitation equipment available 4
• Common pitfall: Leadwire overheating can cause distal tip temperatures up to 57°C, sufficient to cause myocardial tissue damage, increase capture threshold, or complete loss of pacing 5

Contrast-Related Contraindications

• Known allergic reactions to gadolinium are contraindications to gadolinium-based contrast agents 1
• Severe renal insufficiency or acute renal insufficiency due to hepato-renal syndrome contraindicates gadolinium administration 2
• GFR <30 mL/min/1.73m² increases risk of nephrogenic systemic fibrosis with gadolinium contrast 6

Mandatory Screening Requirements

Pre-Scan Evaluation

• All individuals must be thoroughly screened for ferromagnetic materials before entering the MRI suite, including patients and accompanying persons 2
• Remove all metallic items: jewelry, watches, credit cards, clothing with metallic components (zippers, underwire bras), and dental prostheses 2, 3
• Transdermal medication patches containing metal must be removed to prevent thermal burns 2

Standardized Checklist Approach

• Use a written questionnaire followed by oral questioning to identify implants, ports, catheters, metallic implants, vascular stents, coils, active implants, cardiac pacemakers, and foreign bodies 3, 7
• Obtain plain radiographs (anteroposterior and lateral views of chest, abdomen, pelvis) if there is any suspicion of retained foreign bodies 3
• Screen for respiratory depression risk and alcohol use before administering benzodiazepines for claustrophobia 6

Special Considerations

"MRI Conditional" Devices

• These devices require specific conditions to be met: field strength limits (typically 1.5T or 3T), positioning requirements, and specific scanning parameters 3
• Always verify the exact conditions under which a conditional device can be safely scanned 3

Thermal Injury Prevention

• Electrical conductive materials in contact with tissue can cause severe burns from radiofrequency magnetic fields 2
• Heating effects may occur without visible displacement, particularly with conductive loops 2
• Patients should wear cotton clothing free of metal components to prevent thermal burns 2

Pregnancy

• While not an absolute contraindication, MRI safety during pregnancy requires careful consideration and appropriate protocols 8

Critical Safety Measures

Emergency Preparedness

• Document emergency protocols for cardiac arrest, magnet quench, and fire in the MRI suite 2
• All emergency equipment must be MRI-compatible, including laryngoscope blades, oxygen tanks, and resuscitation equipment 2
• Common pitfall: Oxygen tanks and other ferromagnetic equipment can become lethal missiles—the most serious reported injury occurred when an oxygen tank struck a patient's face 7

Monitoring Requirements

• MRI-compatible monitoring equipment must be used for sedated patients, with pulse oximeters and capnographs positioned far from the magnetic coil 2
• Avoid monitoring wires in sedated or restrained patients to prevent thermal injuries 2