Estimating the time of death with infrared tympanic thermometer: a new prospective study in France

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.

Next-generation time of death estimation: combining surrogate model-based parameter optimization and numerical thermodynamics

The postmortem interval (PMI), i.e. the time since death, plays a key role in forensic investigations, as it aids in the reconstruction of the timeline of events. Currently, the standard method for PMI estimation empirically correlates rectal temperatures and PMIs, frequently necessitating subjective correction factors. To address this shortcoming, numerical thermodynamic algorithms have recently been developed, providing rigorous methods to simulate postmortem body temperatures. Comparing these with measured body temperatures then allows non-subjective PMI determination. This approach, however, hinges on knowledge of two thermodynamic input parameters, which are often irretrievable in forensic practice: the ambient temperature prior to discovery of the body and the body temperature at the time of death (perimortem). Here, we overcome this critical limitation by combining numerical thermodynamic modelling with surrogate model-based parameter optimization. This hybrid computational framework predicts the two unknown parameters directly from the measured postmortem body temperatures. Moreover, by substantially reducing computation times (compared with conventional optimization algorithms), this powerful approach is uniquely suited for use directly at the crime scene. Crucially, we validated this method on deceased human bodies and achieved the lowest PMI estimation errors to date (0.18 h ± 0.77 h). Together, these aspects fundamentally expand the applicability of numerical thermodynamic PMI estimation.

Individualised and non-contact post-mortem interval determination of human bodies using visible and thermal 3D imaging

Determining the time since death, i.e., post-mortem interval (PMI), often plays a key role in forensic investigations. The current standard PMI-estimation method empirically correlates rectal temperatures and PMIs, frequently necessitating subjective correction factors. To overcome this, we previously developed a thermodynamic finite-difference (TFD) algorithm, providing a rigorous method to simulate post-mortem temperatures of bodies assuming a straight posture. However, in forensic practice, bodies are often found in non-straight postures, potentially limiting applicability of this algorithm in these cases. Here, we develop an individualised approach, enabling PMI reconstruction for bodies in arbitrary postures, by combining photogrammetry and TFD modelling. Utilising thermal photogrammetry, this approach also represents the first non-contact method for PMI reconstruction. The performed lab and crime scene validations reveal PMI reconstruction accuracies of 0.26 h ± 1.38 h for true PMIs between 2 h and 35 h and total procedural durations of ~15 min. Together, these findings broaden the potential applicability of TFD-based PMI reconstruction.

Establishing the time since death (TSD) is vital in many forensic investigations. By combining thermometry, photogrammetry and numerical thermodynamic modelling, the TSD can be determined non-invasively for bodies of arbitrary shape and posture with an unprecedented accuracy of 0.26 h ± 1.38 h.

Infrared thermography as a modality for tracking cutaneous temperature change and post-mortem interval in the critical care setting

PURPOSE

To evaluate the potential use of cutaneous facial temperature change as measured by an infrared camera as a marker of postmortem interval (PMI) in the minutes immediately following death.

METHODS

This was a prospective, observational pilot study using a convenience sample of all deaths which occurred in a room in an Intensive Care Unit equipped with a ceiling mounted thermal camera. Cutaneous temperature measurements were taken from 60 min antemortem to as long as possible postmortem.

RESULTS

A total of 134 separate measurements was taken from 5 patients, with 65 occurring antemortem, and 69 occurring post-mortem. The longest recorded post-mortem time was 130 min. A Kruskal-Wallis ANOVA testing the hypothesis that there was a difference in facial temperature at each of the different timepoints showed significance (p = 0.029). Post-Hoc comparisons were then performed to compare median temperature values at each timeframe to the baseline value. Compared to baseline, there was a significant difference in facial temperature at 30, 60, and 90 min (p = 0.007, p = 0.01, p = 0.016) (Table 2).

CONCLUSION

There is a statistically significant cutaneous facial temperature change in patients immediately following death as measured by a thermal camera. There is potential for infrared thermography to identify changes immediately before and after death in environments where traditional temperature measurement cannot be accomplished. More work needs to be done to confirm whether a precise postmortem interval (PMI) could be derived from these values.

Estimation of the time since death based on body cooling: a comparative study of four temperature-based methods

The estimation of the time since death is an important task in forensic medicine that mainly relies on body cooling in the early post-mortem period. The rectum has been traditionally used to determine the central core temperature after death, though the external auditory canal has been proposed as an alternative site by several authors. The objective of this study was to assess the ability of four body temperature-based methods (Henssge's rectal nomogram, Henssge's brain nomogram, and Baccino's both interval and global formulae based on ear temperature) to estimate the post-mortem interval (PMI). PMI calculations were carried out based on ear and rectal temperature measurements performed with a reference metal probe on 100 inpatient bodies with an average PMI of 4.5 ± 2.5 h. For practical purposes, ear temperature measurements were applied to Henssge's brain nomogram. All methods could be applied to 81 cases, since high body temperatures prevented the rectal nomogram method from being used in most of the remaining cases. The actual PMI was within the time interval (95% CI) provided by the rectal nomogram method in 72.8% of cases, and in 63.0% to 76.5% of cases when using ear temperature-based methods. The proportions of adequate estimates did not differ statistically between the different methods. When the methods failed to provide a reliable time interval, all except the brain nomogram tended to underestimate the PMI. Similar results were obtained in the subgroup of normothermic patients at the time of death (n = 63), confirming that the PMI calculations had not been biased by the inclusion of patients with thermoregulation disorders. Our findings are in accordance with the published literature which suggests that ear temperature-based methods are as reliable as those based on rectal temperature for estimating the early PMI and that they may be used as quick, simple, and non-invasive methods at the scene, although caution should be taken in interpreting their results given their high error rates. However, further research including field studies is recommended to confirm their practical relevance in forensic casework.

Is infrared thermometry suitable for the determination of the time since death based on ear temperature? A comparative study of two measurement methods

Infrared thermometry has been proposed as an interesting alternative to probe thermometers for recording ear temperature in cadavers to estimate the postmortem interval (PMI), but it has still to be validated in this setting. Our objective was to compare the performance of an infrared thermometer to that of a reference probe thermometer for measuring ear temperature. Temperature measurements were performed on 100 cadavers (mean PMI: 4.5 ± 2.5 h) using the infrared and the probe thermometers. The repeatability of the measurements, their correlation, and the agreement between both methods were evaluated. We showed a good repeatability of the measurements with the infrared thermometer (Lin's concordance correlation coefficient (CCC) = 0.93 [0.72;0.98] for the right ear; CCC = 0.94 [0.75;0.98] for the left ear), and there was a strong and significant correlation between measurements provided by the two instruments (p < 0.001). However, a poor agreement was found between both methods, with a systematic underestimation of about 2 °C of the ear temperature when measured with the infrared thermometer. Data from auricular infrared thermometry should not be applied to algorithms developed for probe thermometers to estimate the PMI. Further research is needed to develop a reliable algorithm specifically based on infrared thermometry.