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

Lodged bullets on computed tomography: Three classification procedures for the virtual investigation of bullets or their fragments that cannot be recovered from the living patient

“…Since the reconstruction parameters for clinical CT data are set to aid the diagnostic assessment of injuries for medical treatment, the visual assessment of a radiopaque bullet is very limited on standard CT images. 7 Furthermore, metallic objects cause metal artefacts on CT. Although metal artefact reduction algorithms are routinely applied to improve the image quality and reduce the bright and dark streaks caused by metallic objects, these reconstruction algorithms do not improve the visualisation of a lodged bullet.…”

“…12 Deformed bullets, in turn, may be classifiable according to their deformation pattern; for instance, expanding bullets, such as soft-point and hollow-point bullets, can be inferred if the bullet presents a mushroom shape, while full metal jacket bullets usually remain intact or fragment after striking or perforating bone. 7 The degree of mushrooming can provide further information on the bullet. Bullets from special police ammunition, such as Action 4 bullets (Figure 1), are designed to present only very slight mushrooming because of their specific designs or rather their hollowed cores, which can be delineated on CT as well.…”

“…Distance-measuring tools provided by any standard visualisation software can be used to investigate the bullet dimension in situ. 7,11,19 Since CT data allow the rotation of a captured object on the screen, a lodged bullet can be easily aligned to its short axis and long axis for measurements of the calibre and size, respectively. Reconstructions with small voxels improve the accuracy of the measured results.…”

“…Even if bullets are deformed, the calibre estimations can be quite accurate, with a mean difference of 0.09 mm (standard deviation¼0.31 mm) from the actual calibre. 7 It is important to perform such measurements at an appropriate location on the bullet in order to avoid overestimations; for instance, the calibres of mushroom-shaped bullets must be measured at the rear end of the bullet to obtain a valid result. 7 Calibre measurements of shot pellets, however, are potentially inaccurate: due to their spherical shape, the diameter decreases or increases, depending on the Figure 1.…”

“…7 It is important to perform such measurements at an appropriate location on the bullet in order to avoid overestimations; for instance, the calibres of mushroom-shaped bullets must be measured at the rear end of the bullet to obtain a valid result. 7 Calibre measurements of shot pellets, however, are potentially inaccurate: due to their spherical shape, the diameter decreases or increases, depending on the Figure 1. An intact Action 4 bullet (left side) and a deformed Action 4 bullet with a characteristic slight mushrooming (right side).…”