Towards a rapid diagnosis of highly decomposed bodies in PMCT: The QuickRAI

The Radiological Alteration Index (RAI) is a scale developed to quantify the degree of putrefaction in corpses using post-mortem CT scans. It is based on a staging system with four grades (0 to III) corresponding to the gaseous infiltration of seven tissue sites (heart, liver, subcutaneous pectoral tissue, left innominate vena, third lumbar vertebra, abdominal aorta, and kidney). The total RAI, obtained by summing the scores of each site, ranging from 0 (fresh body) to 100 (highly decomposed body). In the field of forensic anthropology, it has been shown that age-at-death estimation based on bone density measurements from post-mortem CT scans (PMCT) is not applicable to highly decomposed bodies with a RAI score ≥ 80. In this context, we analysed the RAIs of 200 post-mortem CT scans to identify criteria that would allow for the quicker identification of bodies high putrefied bodies (with a RAI ≥80), without calculating the total score. We developed a decision tree that allows for the determination of a RAI< 80 in 2 steps. Our results showed a significant correlation between a grade III in three specific sites (the kidney, subcutaneous pectoral tissue, and L3 vertebra) and a RAI ≥ 80. Our two-step method involves only examining one site with late-stage putrefaction and another with early-stage putrefaction. The QuickRAI demonstrated performance equivalent to the gold standard (RAI) for identifying highly decomposed bodies (RAI ≥ 80), with almost perfect agreement (Cohen's kappa = 0.98) and excellent diagnostic accuracy (sensitivity 1, specificity 0.96, PPV 0.91, and NPV 1). This observation allows for the quick identification of bodies in which putrefactive alterations affect all tissues, including bone. Then, the QuickRAI could simplify the age estimation process on PMCT and facilitate research efforts in this field.