Forensic shotgun pellet examination - material detection with dual-energy computed tomography

Forensic shotgun wounds are relatively common worldwide. Shotguns are used for legal purposes such as hunting as well as for criminal activities. In addition, shotguns are used by military and law enforcement. Even though shotguns are often lethal from close distances, shotgun wounds require medical attention regardless of the shooting distance. As a result, patients with shotgun wounds are often treated in hospitals, and in lethal incidents, they are examined by forensic pathologists. Radiological imaging, computed tomography (CT) in particular, may constitute a part of the shotgun wound examination in both scenarios. CT may help to identify and locate the pellets and aid in wound characterization. It would be important to detect the pellet material as lead pellets, for example, are heavily toxic, and others, such as steel pellets may, as ferromagnetic, prevent some further imaging modalities such as magnetic resonance imaging from being employed. In this study, we wanted to experiment whether shotgun pellet material could be detected with radiological imaging utilizing dual-energy CT (DECT). Traditionally pellets are manufactured from heavily toxic lead, but due to environmental factors, other pellet materials such as steel, copper, tungsten, and bismuth are getting more and more popular. To conduct this study, various pellet materials were shot into ballistic gelatine blocks. The blocks then underwent DECT. Subsequently, each pellet was automatically segmented, and for these extracted pellets a dual-energy index (DEI) was computed. DEI values of the pellets were compared to determine whether this measure could be used to differentiate between the pellet materials. The DEI values (mean ± standard deviation) were 0.212 ± 0.006, 0.008 ± 0.001, 0.187 ± 0.002, 0.012 ± 0.004, and 0.008 ± 0.002 for steel, lead, copper, tungsten, and bismuth, respectively. The Wilcoxon rank sum test indicated that steel and copper pellets could be reliably differentiated from the other pellet materials. Our study demonstrated that DECT can reliably differentiate steel and copper shotgun pellets from other materials such as lead, tungsten, and bismuth. This capability may provide important additional information in medico-legal investigations and aid trauma centres treating patients with shotgun wounds.