MR of Ballistic Materials : Imaging

The most common ballistic materials available in the urban setting were studied for their MR effects on deflection force, rotation, heating, and imaging artifacts at 1.5 T to determine the potential efficacy and safety for imaging patients with ballistic injuries. The 28 missiles tested covered the range of bullet types and materials suggested by the Cleveland Police Department. The deflection force was measured by the New method. Rotation was evaluated 30 min after bullets had been placed in a 10% (weight per weight) ballistic gelatin designed to simulate brain tissue, with the long axis of the bullet placed parallel and perpendicular to the i axis of the magnet. Heating was measured with alcohol thermometers by imaging for 1 hr alternatively with gradientecho and spin-echo sequences (RF absorption = 0.033 and 0.326 w /kg respectively). Image artifacts on routine sequences were evaluated. All the steel-containing bullets except for the Winchester armor-piercing 38 caliber exhibited deflection. A nonsteel 7.38-mm Mauser also deflected. Deflection range was 514 to 15,504 dynes. Rotation occurred when the bullets were not parallel to the Z axis. Temperature changes were not significant. Deflecting projectiles resulted in obliteration of the image. The artifacts from other projectiles were small but varied by content. The artifact of the Winchester armor-piercing 38-caliber bullet was similar to those without steel. Bullets that contain steel or ferromagnetic contaminates such as nickel can be rotated within the MR unit. Ferromagnetic contaminants do not allow nonsteel bullets to be imaged with confidence; the potential rotation and movement of these missiles results in a relative contraindication to MR, although location within the body and time since injury may be modifying conditions. Missiles with nonaustenitic steel or nickel in the area of interest make images useless, while projectiles without these materials cause minimal image distortion and signal void.