Diagnostic accuracy of rib fracture detection in forensic post-mortem photon counting CT.

Background: Recently, post-mortem photon-counting CT (PMPCCT) has been introduced to forensic imaging. Compared to conventional energy integrating post-mortem CT (PMCT), PMPCCT enables ultra-high resolution (UHR) imaging, which is particularly suitable for visualizing fine fractures and fissures. These are often found in rib trauma, which is usually relevant in forensic medicine. The aim of this study was to evaluate the diagnostic accuracy of rib fracture detection using PMPCCT compared to PMCT and forensic autopsy.

Methods: A total of n = 20 bodies that had suffered blunt chest trauma before death and n = 5 non-trauma control cases were investigated. PMCT and PMPCCT were conducted prior to forensic autopsy. Two observers (radiologist and forensic pathologist) analyzed PMCT images (reconstructed with a slice thickness of 0.5 mm in a 512 matrix) and PMPCCT images (reconstructed with slice thicknesses of 0.5 mm and 0.2 mm (UHR) in a 1024 matrix). Imaging diagnosis of rib fractures was compared to autopsy diagnosis as gold standard. The diagnosis of different types of rib fractures assessed at imaging was compared between PMCT and PMPCCT.

Results: Inter-rater agreement between the two observers was good (κ = 0.79). Both PMCT and PMPCCT diagnosed less rib fractures than the autopsy (n = 356 fractures). Compared to PMCT, UHR-PMPCCT demonstrated slightly higher sensitivity (e.g., 92% vs. 82% in observer 1), slightly higher specificity (e.g., 97% vs. 95%), and lower positive predictive value (e.g., 75% vs. 82%) for the diagnosis of all rib fractures. Chi-squared tests showed significant differences (p-value < 0.05 in both observers) between UHR-PMPCCT and PMCT for the diagnosis of incomplete rib fractures with visible dehiscence of one cortical line.

Conclusion: Based on the results, it is questionable whether PMPCCT offers additional forensic value over PMCT for the specific forensic issue of diagnosing rib fractures.