Background and purpose: Gunshot injuries have been considered a contraindication for MRI because of the risk of secondary dislodgement of retained metallic foreign bodies. The objective of our study was to provide a systematic overview of the behaviour of projectiles and fragments in order to aid decision-making regarding the use of MRI in clinical practice.
Materials and methods: Ferromagnetic (n = 2) and non-ferromagnetic (n = 5) projectiles and fragments that were lodged in soft tissue (porcine masseter muscles) were examined using standard protocols at 1, 1.5 and 3 T, to simulate clinical situations as realistically as possible. CT was performed before and after every MRI to assess rotation and movement. Artefacts and image quality were analysed using Likert-type scales.
Results: Ferromagnetic projectiles were of poorer quality and showed larger artefacts and did not provide benefit for clinical practice compared to images of non-ferromagnetic material. Image quality of non-ferromagnetic projectiles varied widely (from very good to moderate) depending on the composition of the projectiles. Field strength (1 T to 3 T) had no relevant influence on image quality.
Conclusions: Non-ferromagnetic projectiles are not a contraindication for MR imaging since there is no potential risk of secondary dislodgement. Image quality and the extent of artefacts, however, strongly depend on the type of ammunition used. The presence of ferromagnetic projectiles in or near vital anatomic structures is a contraindication for MRI because these objects may exhibit movement in response to magnetic fields. Knowledge of the type of projectile used appears to be important in order to guide patient management before an examination is performed. So, the production and use of projectiles suitable for MRI should be favored in the future, knowing that this will be hard to fulfil.
Keywords: Artefacts; Gunshot injuries; MRI; Projectiles; Safety.
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