Correlation of CT measurements of total body gas volume and hounsfield units with post-mortem interval

Background: Accurate estimation of the post-mortem interval (PMI) may be a matter of crucial importance in forensic investigations. A preliminary investigation to assess whether longitudinal changes in organ Hounsfield units (HU) and total body gas volume (TBGV), as measured from serial PMCT scans, correlate with postmortem interval (PMI). Materials and Methods: Eight euthanised lambs each had five whole body CT scans performed over seven days and measurements were taken from the brain, heart, lungs, liver, kidneys and spleen. HU tissue density was measured directly from the PMCT images, while TBGV was calculated using ImageJ software. A random effect model was fitted with the subject fitted as a random intercept. Ethical and Animal Welfare approval was obtained. Results: The average increase in TBGV was 422 ml/Kg with a change of 77 ml/Kg per day. For each additional post-mortem day, the HU of the brain, heart, lung, liver and spleen decreased by per day since death, while HU for the kidneys increased by day since death. Conclusion: Expect for the kidney where it increased, there was clear and progressive decrease in tissue densities and for all organs there was an increase in TBGV over time. However, the overlap in values between cases indicates that more work is required before either HU or TBGV can be developed as non-invasive methods to reliably determine time of death in humans.