Heavy metal in radiology: how to reliably differentiate between lodged copper and lead bullets using CT numbers.

BACKGROUND: The in situ classification of bullets is of interest in forensic investigations when the bullet cannot be removed. Although computed tomography (CT) is usually performed on shooting victims, visual assessment, or caliber measurements using CT can be challenging or infeasible if the bullets are deformed or fragmented. Independent from the bullet's intactness, x-ray attenuation values (CT numbers) may provide information regarding the material of the bullet. METHODS: Ethical approval was not required (animal cadavers) or waived by the ethics committee (decedents). Copper and lead bullets were fired into animal cadavers, which then underwent CT scanning at four energy levels (80, 100, 120, and 140 kVp). CT numbers were measured within regions of interest (ROIs). In addition to comparing CT numbers, the dual-energy index (DEI), representing the ratio between the CT numbers of two energy levels, was calculated. The most appropriate method was applied for decedents with fatal gunshot wounds. RESULTS: CT numbers demonstrated no significant difference between copper and lead bullets, and false classifications can easily occur. DEI calculations revealed significant differences between the two groups of bullets. The 120/140 DEIs calculated from the maximum CT numbers obtained from ROIs at the edge of copper versus lead bullets presented a significant difference (p = 0.002) and a gap between the CT numbers of copper and lead bullets and was successfully applied for the decedents. CONCLUSIONS: This study presents a viable method for distinguishing copper and lead bullets in situ via CT and highlights the potential pitfalls of incorrect classifications.

Visualization and material-based differentiation of lodged projectiles by extended CT scale and the dual-energy index.

Computed tomography (CT) scans of gunshot wounds and their high sensitivity in detecting osseous lesions has often been reported in the literature. However, studies concerning in situ examinations of lodged projectiles with CT to determine the ammunition used are lacking. Projectile visualizations are hampered in standard CT due to the presence of metal artifacts and the limited range of Hounsfield units (HU). The use of special reconstruction algorithms can overcome these limitations. For instance, using extended CT scale (ECTS) reconstruction supports detailed visualizations of metallic objects. In addition to projectile visualizations, X-ray attenuation measurements (CT numbers) of metallic objects can be used to differentiate materials in CT. This study uses real forensic cases to demonstrate that-depending on the degree of deformation-a detailed visualization of lodged projectiles using ECTS can provide useful information regarding the ammunition used and allows accurate caliber measurements. Independent from the degree of deformation, the in situ classification of bullets, even fragmented bullets, according to their metallic components is feasible by dual-energy index (DEI) calculations. The assessment of a lodged projectile with CT images provides useful information on the case; thus, a close examination of lodged projectiles or bullet fragments should be a part of the overall radiological examination for cases of penetrating gunshot wounds.

Identification of Bullets Based on Their Metallic Components and X-Ray Attenuation Characteristics at Different Energy Levels on CT.

OBJECTIVE. This study aimed to identify bullets on the basis of their metallic components and to distinguish between ferromagnetic and nonferromagnetic bullets using CT. MATERIALS AND METHODS. Eight ferromagnetic, steel-jacketed lead bullets, four nonferromagnetic, non-steel-jacketed lead bullets, and four nonferromagnetic solid bullets composed of copper or copper and zinc alloys which we refer to here as "Cu(Zn) bullets," were scanned by CT at 80, 100, 120, and 140 kVp. Attenuation values (in Hounsfield units) were measured on an extended CT scale (ECTS) in the core and at the edge of the bullets and were used to calculate the dual-energy index (DEI). RESULTS. Although all nonferromagnetic bullets significantly differed from ferromagnetic bullets, the significant differences were solely attributed to the higher DEI of solid Cu(Zn) bullets compared with that of all-lead bullets. The lead bullets with ferromagnetic, steel-containing jackets did not differ from the lead bullets with nonferromagnetic, non-steel-containing jackets on the basis of DEIs obtained from core and edge measurements. Solid Cu(Zn) bullets could be clearly distinguished from lead bullets regardless of the metallic components of the jackets using DEI calculations from CT numbers on an ECTS. The DEIs based on the dual-energy pair 120 and 140 kVp appear to be the most appropriate for distinguishing between these two types of bullets. CONCLUSION. This study provides new scientific knowledge regarding metals and their characteristics at different tube voltage levels. The abilities of clinically approved dual-energy CT allow differentiation of bullets composed of low-atomic-number (Z) metals from bullets composed of high-Z metals via DEI calculations from CT numbers on an ECTS.