1.6. Forensic safety of MRI in gunshot victims

Purpose Multi-detector computed tomography (MDCT) has proven to be of value for the reconstruction of trajectories of projectiles and the assessment of the injuries. However for the depiction of soft tissue injury MRI is superior to MDCT and MRI may be of value to assess trajectories through soft tissue. In a clinical setting there are guidelines for the application of MRI in patients with projectiles or fragments and with certain precautions MRI is safe for these patients. However this has not been studied from a forensic point of view. Subjects and method To assess the behaviour of three projectile types in a 1.5 and 3 T MRI system, projectiles were placed in seven gelatine phantoms with mechanical characteristic of human muscle tissue. Projectiles were placed with and without a simulated trajectory. Before and after exposure to the magnetic field the gels were scanned on CT assess of the projectiles. Results The ferromagnetic projectiles tend to rotate parallel to the z -axis of the magnetic field and 5 out of the 7 projectiles moved through the phantom, either through the simulated trajectory or a new trajectory. This was observed in both the 1.5 and 3 T system. Due to extensive susceptibility artefacts the anatomy around the projectile was not visible. Conclusion Ferro-magnetic projectiles rotate and migrate in a gelatine phantom. It is very likely these projectiles will also migrate in a human body in a MRI system. Therefore we conclude that MRI is not forensic safe in these instances.