Influence of the ear temperature range on the measurement bias between an infrared thermometer and a reference probe for post-mortem interval determination.

The aim of this study was to assess the influence of the post-mortem outer ear temperature (OET) on the measurement bias previously observed for short post-mortem intervals (PMI) between a commercially available infrared thermometer and a reference metal probe thermometer. To that end, 100 refrigerated bodies were added to our initial cohort to investigate lower OET. In contrast to our previous findings, a very good concordance was noted between both methods. There was still an overall underestimation of ear temperatures with the infrared thermometer, but the average bias was significantly reduced compared to that observed in the initial cohort (1.47 °C for the right ear and 1.32 °C for the left ear). Most importantly, this bias progressively decreased as the OET decreased, becoming negligible for OET lower than 20 °C. These results are in agreement with literature data regarding these temperature ranges. The discrepancy observed with our previous observations may be due to the technical characteristics of the infrared thermometers. The lower the temperatures measured, the more the measurements approach the lower limit of the measuring range of the device and tend to give constant values, resulting in a smaller underestimation of the measurements. Further research is needed to assess the interest of integrating in the already validated OET-based formulae a variable dependent on the temperature measured with the infrared thermometer, to eventually allow infrared thermometry to be used for PMI estimation in forensic practice.