Metallic ballistic fragments: MR imaging safety and artifacts

Area of Science:

• Medical Imaging
• Materials Science
• Forensic Science

Background:

• Metallic foreign bodies, such as bullets and shotgun pellets, can cause artifacts in magnetic resonance imaging (MRI).
• The magnetic properties of these metallic objects can influence their behavior within an MRI scanner.
• Understanding the ferromagnetism of bullets is crucial for interpreting MRI scans and ensuring patient safety.

Purpose of the Study:

• To evaluate the ferromagnetism of various bullets and shotgun pellets.
• To assess the impact of ferromagnetic bullets on magnetic resonance imaging (MRI) quality.
• To review clinical cases of patients with retained metallic foreign bodies undergoing MRI.

Main Methods:

• In vitro testing of metallic specimens (bullets and pellets) for ferromagnetism using magnetic deflection.
• Assessment of artifact generation in spin-echo and gradient-echo MRI sequences.
• Review of seven patient cases with retained metallic foreign bodies imaged with MRI.

Main Results:

• Four out of 21 tested bullets demonstrated marked ferromagnetism, likely due to steel content or impurities.
• Ferromagnetic bullets caused severe MRI artifacts and image distortion.
• Nonferromagnetic bullets and pellets produced mild to moderate artifacts.
• Most patients (6/7) with retained metallic foreign bodies experienced only mild MRI artifacts; intracranial shrapnel caused significant artifact.

Conclusions:

• Ferromagnetic bullets can cause substantial MRI artifacts, unlike most nonferromagnetic pellets and bullets.
• While most retained metallic foreign bodies are safe for MRI, caution is advised, especially with ferromagnetic materials or those near critical structures.
• Further investigation into bullet composition and its impact on medical imaging is warranted.