Can a patient with a retained bullet (foreign body) in their chest undergo a Magnetic Resonance Imaging (MRI) scan?

MRI Safety in Patients with Retained Bullets

A patient with an old bullet in her chest can likely undergo MRI safely, but this depends critically on whether the bullet is ferromagnetic—most modern civilian bullets are non-ferromagnetic and MRI-safe, but radiographic screening with X-ray or CT must be performed first to assess bullet composition and exclude ferromagnetic projectiles that could move or heat dangerously near vital structures. 1

Determining Bullet Composition Before MRI

The key decision point is identifying whether the retained bullet is ferromagnetic or non-ferromagnetic, which can be accomplished through radiographic assessment:

• Radiography and CT can reliably predict bullet composition by examining specific imaging characteristics 1
• Non-ferromagnetic bullets appear intact without deformation or debris trails on imaging 1
• Ferromagnetic bullets demonstrate a characteristic debris trail and deformation of the primary projectile on radiographs and CT 1
• This imaging-based assessment allows triage of patients who were previously denied MRI simply because bullet composition could not be determined 1

Safety Profile by Bullet Type

Non-Ferromagnetic Bullets (MRI-Safe)

Most modern civilian ammunition is non-ferromagnetic and poses minimal risk:

• Non-ferromagnetic bullets showed no torque forces or movement at 1.5T MRI in testing 1
• These projectiles produce only mild to moderate metal artifacts that do not preclude diagnostic imaging 2, 1
• Heating above the FDA limit of 2°C was not observed in any projectiles tested at 1.5T 1
• Image quality with non-ferromagnetic bullets ranges from very good to moderate depending on specific composition 3
• Field strength (1T to 3T) has no relevant influence on safety or image quality 3

Ferromagnetic Bullets (MRI Contraindication)

Ferromagnetic bullets pose significant risks and are contraindicated for MRI:

• Four of 21 metallic specimens tested demonstrated marked ferromagnetism, with three manufactured outside the United States 2
• Ferromagnetic bullets readily rotated within gelatin phantoms in response to magnetic torque 2
• These projectiles create severe MR artifacts and image distortion that limit diagnostic utility 2
• The presence of ferromagnetic projectiles in or near vital anatomic structures (heart, great vessels, neural tissue) is an absolute contraindication for MRI due to potential secondary dislodgement 3

Clinical Algorithm for Decision-Making

Follow this stepwise approach:

1. Obtain chest radiograph or review existing CT imaging to identify the bullet and assess for ferromagnetic characteristics 1

2. Look for these specific imaging features:

   • Debris trail surrounding the bullet = ferromagnetic (MRI contraindicated) 1
   • Bullet deformation or fragmentation = ferromagnetic (MRI contraindicated) 1
   • Intact bullet without debris = likely non-ferromagnetic (MRI likely safe) 1

3. Assess anatomic location:

   • Bullets near the heart, great vessels, or other vital structures require extra caution even if non-ferromagnetic 2
   • Bullets embedded in soft tissue away from critical structures pose lower risk 2

4. Consider time since injury:

   • "Old" bullets (your patient's scenario) are typically encapsulated by fibrous tissue, which reduces but does not eliminate movement risk for ferromagnetic projectiles 2

5. If imaging characteristics suggest non-ferromagnetic composition and the bullet is not immediately adjacent to vital structures, MRI can proceed safely 1, 3

Critical Caveats and Pitfalls

Avoid these common errors:

• Never assume all bullets are MRI-safe—approximately 19% of tested bullets were ferromagnetic 2
• Steel-containing bullets, air gun pellets with steel cores, and foreign-manufactured ammunition have higher ferromagnetic rates 2, 4
• The absence of shell casings (common in clinical practice) previously prevented composition determination, but imaging characteristics now allow this assessment 1
• Intracranial shrapnel (presumably steel) creates significant artifact and poses higher risk than bullets in other locations 2
• Even non-ferromagnetic bullets create artifacts that may limit diagnostic quality in the immediate vicinity of the projectile 2, 1

Practical Recommendation for Your Patient

For a patient with an old bullet in the chest:

• Obtain or review chest radiograph/CT to assess bullet characteristics 1
• If imaging shows an intact bullet without debris trail, MRI is likely safe at 1.5T 1
• Document the bullet's distance from the heart and great vessels 2
• If any uncertainty exists about ferromagnetic properties or the bullet is immediately adjacent to vital cardiac or vascular structures, alternative imaging (CT) should be used instead 2, 3
• Consider starting at 1.5T rather than 3T if MRI proceeds, though field strength does not significantly affect safety for non-ferromagnetic projectiles 3