gms | German Medical Science

Objective: Incorporated metallic foreign bodies are still a problem when an MRI is needed. This applies especially for acute gunshot injuries, which are considerer in most cases as a contraindication. The objective of our study was to determine the behavior of different standard ammunition in a magnetic field to aid decision-making in clinical practice, and to assess their impact on image quality.

Methods: 7 different projectiles (1 strong ferromagnetic, 1 weak ferromag. and 5 non- ferromag.) were examined using a soft tissue model (M. masseter of a pig). Standardized MRI protocols with different puls sequences were performed at 1, 1.5 and 3T. Additionally a CT scan was done before and after every MRI to evaluate for rotation and movement of the projectiles.

Results: Non-ferromagnetic projectiles showed no potential risk of secondary dislodgement, but image quality varied widely (from very good to moderate), depending on the exact composition of the projectiles. The weak ferromag. Projectile also caused no problem, while the strongly ferromag. projectile dislodged, so being a contraindication for MRI-Scan.

Spin echo sequences were far superior to any other puls sequence used, but the strength of the magnetic field (1–3 T) did not have a relevant influence on image quality and artefact extent.

Conclusion: Acute Gunshot injuries with an incorporated projectile are no absolute contraindication for MRI, as long as the type of projectile and their behavior in a magnetic field is known. Nevertheless, knowledge of the projectile is also essential, to know the extent of the expected artefacts caused by it. Certain sequences should be avoided (GRE/T2*/SWI) to keep image quality at a maximum. For the future, manufactures should be encouraged to produce MRI compatible ammunition, at least for special purposes (e.g. police).