Bullet characterization using Photon-Counting detector CT: A phantom study with intact bullets

OBJECTIVES: Photon-counting detector CT (PCD-CT) is expected to substantially improve and expand CT-imaging applicability due to its intrinsic spectral capabilities, increased spatial resolution, reduced electronic noise, and improved image contrast. The current study aim is to evaluate PCD-CT efficacy in characterizing bullets based on their dimensions, shape, and material composition. MATERIALS AND METHODS: This is an observational phantom study examining 11 unfired, intact bullets of various common calibers, placed in ballistic gelatin. Ultra-high resolution and spectral images were acquired on a clinical PCD-CT-scanner. CT-measurements of the dimensions (length and diameter) were independently determined by 2 readers and compared to previously obtained manual caliper measurements. Bullet shape (round nose, flat nose, or spitzer bullet) was assessed using 3D-volume rendered (3D-VR) CT-image reconstruction. Bullet composition was examined based on dual-energy ratios (DER) which were color-coded accordingly and overlaid on high resolution CT-images. RESULTS: Compared to caliper measurements, mean differences (SD) in bullet diameter were + 0.40 mm (0.16) and + 0.38 mm (0.13) for readers 1 and 2; mean differences in length were + 0.49 mm (0.19) and + 0.45 mm (0.20). The observed proportion of accurately categorized 3D-VR reconstructions was 90.9 % (10/11) for both readers with moderate interrater agreement (Cohens ?: 0.59, P = 0.004). DER color-coded images showed clear distinction between jacket and core and enabled correct identification of bullets with and without jackets. CONCLUSIONS: These results indicate that PCD-CT is a promising tool for reliable radiological characterization of bullets.