Examination of postmortem changes in the lungs, trachea, and bronchi in a rat model imaged with small-animal computed tomography

Abstract

Objectives: As less autopsies are performed, the need for postmortem computed tomography (PMCT) as an alternative is increasing. It is important to know how postmortem changes over time are reflected on CT, in order to improve the diagnostic capability of PMCT and replace forensic pathology evaluations such as time of death estimation.

Methods: In this study, we examined temporal changes on postmortem chest CT images of a rat model. After acquiring antemortem images under isoflurane inhalation anesthesia, the rats were euthanized with a rapid intravenous injection of anesthetics. From immediately after death to 48 hours postmortem, chest images were acquired using small-animal CT. The 3D images were then evaluated on a workstation to measure the antemortem and postmortem air content in the lungs, trachea, and bronchi over time.

Results: The air content in the lungs decreased, but the air content of the trachea and bronchi temporarily increased 1-12 hours postmortem, then decreased at 48 hours postmortem. Therefore, the measurement of trachea and bronchi volumes on PMCT could be an objective way to estimate the time of death.

Conclusions: While the air content of the lungs decreased, the volume of the trachea and bronchi temporarily increased after death, indicating the potential to use such measurements to estimate time of death.

Keywords: Computed tomography; Forensic radiology; Postmortem change; Trachea volume.

Figure 1

Cross-sectional computed tomography (CT) scan The top image shows the level of tracheal bifurcation, the middle image shows the level of subtracheal bifurcation, and the bottom image shows the base of the lung. Compared with 0 hours, the bronchi expanded 1–12 hours postmortem, then shrank after 24 hours. After 48 hours, the air content decreased and pulmonary edema and congestion were confirmed.

Figure 2

3D image analysis identifies only the trachea and bronchi Compared with 0 hours, the left and right bronchi are thicker at 12 hours postmortem, and peripheral bronchi are clearly identifiable. The air contents of the trachea and bronchi were: 0.2745, 0.3009, 0.3538, 0.5079, 0.4504, and 0.2397 mL at 0, 1, 6, 12, 24, and 48 hours postmortem, respectively.

Figure 3

Air content in the lungs, trachea, and bronchi over time (A) Lungs and (B) trachea and bronchi The air content of the lungs decreased significantly after death (*P<0.05), whereas the air content of the trachea and bronchi increased significantly 1–12 hours postmortem compared with 0 hours (*P<0.05). After 48 hours, the air content significantly decreased (**P<0.05).

Figure 4

Fluid in the trachea and bronchi The bronchus on the ventral side of the right lung (arrow) shows loose air due to fluid accumulation 48 hours postmortem.