Are flexometallic (flexible metal) tubes safe to use in Magnetic Resonance Imaging (MRI) environments?

Flexometallic Endotracheal Tubes in MRI: Safety Assessment

Flexometallic (armored) endotracheal tubes containing metal wire reinforcement are generally contraindicated in the MRI environment due to significant risks of heating, displacement, and potential airway injury from ferromagnetic forces.

Primary Safety Concerns

Ferromagnetic Projectile Risk

• All ferromagnetic objects must be prevented from entering the MRI scanner area as they become dangerous projectiles in the magnetic field 1, 2
• The American College of Radiology mandates comprehensive screening for all ferromagnetic materials before MRI suite entry 2
• Metallic objects experience deflection forces in static magnetic fields ranging from 0.147 to 4.7 Tesla 3

Thermal Injury Risk

• Electrical conductive materials in contact with tissue can cause severe burns when exposed to radiofrequency magnetic fields during MRI scanning 1
• Metal-containing materials must be removed to prevent thermal injuries, similar to the requirement for removing transdermal patches with metallic components 1, 2
• Temperature increases can occur in metallic implants during MRI, though the degree varies by material composition 4, 5

Displacement and Movement Risk

• Ferromagnetic materials experience translocation and rotation forces within the MRI magnetic field 5
• Even materials that appear stable may move during MRI sequences, particularly those with steel components 5
• Stainless steel components showed marked position changes even in lower field strength testing 5

Specific Evidence on Metal Tubes and Wires

Wire-Reinforced Devices

• Gold-plated stainless steel ventilation tubes with wire components demonstrated significant position changes in 7 Tesla MRI testing 5
• Wire components should be removed before MRI to prevent injury, as recommended for ENT ventilation tubes 5
• Retained epicardial pacing wires (cut short at skin) have been studied and found relatively safe at 1-1.5 Tesla, but this does not extrapolate to endotracheal tubes in direct airway contact 6

Material Composition Matters

• Of 127 metallic implants tested, only 66 were completely nonferromagnetic, while 29 showed minimal deflection 3
• Titanium, gold, and platinum alloys demonstrate better MRI compatibility than stainless steel 3, 5
• Pure gold implants showed the least movement in high-field MRI compared to other materials 5

Clinical Decision Algorithm

Absolute Contraindications

• Any endotracheal tube containing ferromagnetic wire reinforcement should not be used in MRI 1, 2
• Standard flexometallic tubes typically contain stainless steel wire spirals, making them unsuitable 5

Alternative Approaches

• Use MR-safe or MR-conditional endotracheal tubes specifically designed and tested for MRI environments 2, 7
• Consider non-wire-reinforced tubes made entirely of non-metallic materials for MRI procedures 2
• Verify the MRI safety classification (MR Safe, MR Conditional, or MR Unsafe) for any airway device before use 2, 7

If Metal-Containing Tube Already in Place

• Do not proceed with MRI if a standard flexometallic tube is present 2
• Replace with an MR-safe alternative before imaging 2
• Document the specific tube model and verify manufacturer specifications for MRI compatibility 7

Critical Pitfalls to Avoid

• Never assume a tube is MRI-safe based solely on "non-ferromagnetic" claims without specific testing data 3
• Do not rely on low-field strength safety data when using 1.5T or 3T clinical scanners 5
• Avoid the misconception that small amounts of metal are always safe—even millimeter-sized fragments can pose risks near vital structures 8
• Remember that heating effects may occur even without visible displacement, particularly with conductive loops 1, 4

Special Considerations for Anesthesia

• Electronic monitoring devices attached to or near the endotracheal tube must also be MRI-compatible 2
• Temperature probes and other monitoring equipment require MR-safe alternatives 2
• Emergency airway equipment in the MRI suite must be entirely MRI-compatible, including laryngoscope blades 2

The safest approach is to use only endotracheal tubes explicitly labeled as MR-safe or MR-conditional by the manufacturer, with documented testing at the specific field strength of your MRI scanner 2, 7.