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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 3  |  Issue : 1  |  Page : 1-8

Estimation of Postmortem Interval Using the Radiological Techniques, Computed Tomography: A Pilot Study


Department of Forensic Medicine, National Police University of China, Shenyang, China

Date of Web Publication31-Mar-2017

Correspondence Address:
Jilong Zheng
No. 83, Tawan Street, Huanggu, 110036, Shenyang
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jfsm.jfsm_4_17

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  Abstract 

Estimation of postmortem interval (PMI) has been an important and difficult subject in the forensic study. It is a primary task of forensic work, and it can help guide the work in field investigation. With the development of computed tomography (CT) technology, CT imaging techniques are now being more frequently applied to the field of forensic medicine. This study used CT imaging techniques to observe area changes in different tissues and organs of rabbits after death and the changing pattern of the average CT values in the organs. The study analyzed the relationship between the CT values of different organs and PMI with the imaging software Max Viewer and obtained multiparameter nonlinear regression equation of the different organs, and the study provided an objective and accurate method and reference information for the estimation of PMI in the forensic medicine. In forensic science, PMI refers to the time interval between the discovery or inspection of corpse and the time of death. CT, magnetic resonance imaging, and other imaging techniques have become important means of clinical examinations over the years. Although some scholars in our country have used modern radiological techniques in various fields of forensic science, such as estimation of injury time, personal identification of bodies, analysis of the cause of death, determination of the causes of injury, and identification of the foreign substances of bodies, there are only a few studies on the estimation of time of death. We detected the process of subtle changes in adult rabbits after death, the shape and size of tissues and organs, and the relationship between adjacent organs in three-dimensional space in an effort to develop new method for the estimation of PMI. The bodies of the dead rabbits were stored at 20°C room temperature, sealed condition, and prevented exposure to flesh flies. The dead rabbits were randomly divided into comparison group and experimental group. The whole-body CT scans were performed on the experimental group of rabbits at different PMIs. NeuViz dual-slice spiral CT scanner (made by Neusoft Medical in China, 2 mm × 10 mm high-speed rare earth ceramic detector) is a 360° scan that could obtain two images, capable of providing a wide range of high-speed continuous spiral scan. Max Viewer (Version: 1.0.0131, Neusoft, Shenyang, China) is a CT image viewing software developed by Neusoft Medical. The software can be used to view and process images in various common methods and to measure a number of parameters, such as length, area, angle, and CT values. Statistical analysis was performed using SPSS1 Statistics 19.0 (SPSS, Inc., Chicago, IL, USA). A P ≤ 0.05 was considered statistically significant. We obtained the binomial regression equation of the CT values and the related coefficient (R2). In the future, we suggests that comprehensive analyses of various indicators of different organs could establish a diversified pattern to remedy the deficiencies and make the study of PMI estimation more scientific and enhance the operability.

Keywords: Area ratio, organ average computed tomography value, overall average computed tomography value, postmortem interval


How to cite this article:
Wang J, Zheng J, Zhang J, Ni S, Zhang B. Estimation of Postmortem Interval Using the Radiological Techniques, Computed Tomography: A Pilot Study. J Forensic Sci Med 2017;3:1-8

How to cite this URL:
Wang J, Zheng J, Zhang J, Ni S, Zhang B. Estimation of Postmortem Interval Using the Radiological Techniques, Computed Tomography: A Pilot Study. J Forensic Sci Med [serial online] 2017 [cited 2017 Oct 23];3:1-8. Available from: http://www.jfsmonline.com/text.asp?2017/3/1/1/203551


  Introduction Top


In forensic science, postmortem interval (PMI) refers to the time interval between the discovery or inspection of corpse and the time of death. Forensic workers usually determine PMI mainly based on postmortem changes, such as livor mortis, body temperature, rigor mortis, vitreous humor changes in conjunction with autopsy findings, such as volume of urine in bladder and degree of digestion of stomach contents, and personal experience in forensic medicine. However, many factors could affect determination of PMI, including individual and environmental factors. No matter which of the above methods are adopted, the determination of PMI shall be subject to certain limitations.

Autopsy is an important process to determine the cause of death, but the traditional autopsy methods destroy the body, and the folk customs and other factors related to the integrity of the body lead to very low autopsy rate in our country. Computed tomography (CT), magnetic resonance imaging (MRI), and other imaging techniques have become important means of clinical examinations over the years.[1] In addition, CT and MRI are also successfully applied to in vivo damage inspection, especially for some invisible damages. However, it was not until the year of 2000 that the research team led by Professor Dirnhofer used imaging techniques in autopsy for the first time. As the autopsy using imaging techniques differs from the conventional autopsy, some foreign scholars referred to it as “virtopsy (virtual autopsy)”[2] or noninvasive anatomy for its characteristics, such as noninvasiveness, rapidness, objectivity, and convenience of preserving data. Furthermore, Jackowski et al. Discovered after performing MRI scans on the corpses in eighty cases of myocardial infarction, all the MRI images of acute, sub-acute, Signal on T1- or T2-weighted imaging can not be detected except the ultra-acute myocardial infarction.[3] They considered that radiological techniques can be used for in situ forensic identification of myocardial infarction according to the changes in signal. The experiment results showed that the noninvasive diagnostic modern imaging techniques have great potential for the development of forensic application.[4]

Although some scholars in our country have used modern radiological techniques in various fields of forensic science, such as estimation of injury time, personal identification of bodies, analysis of the cause of death, determination of the causes of injury, and identification of the foreign substances of bodies, there are only few studies on the estimation of time of death.[5] Chinese scholars, Xiao Jian et al. published their study on the spiral CT scan of rabbit model of air embolism death for the first time in 2006.[6] The scan showed that the changes in CT values and the morphological changes in some organs are associated with the estimation of PMI. This study used modern imaging techniques (spiral CT) for dynamic observation of CT imaging changes in an adult rabbit model after death by hanging at different PMIs, and observed structures of the body, organs, and tissues and their internal changes, and finally performed traditional anatomy for macroscopic comparison of the two methods. Meanwhile, with the help of visualization technology, we detected the process of subtle changes in adult rabbits after death, the shape and size of tissues and organs, and the relationship between adjacent organs in three-dimensional space in an effort to develop a new method for the estimation of PMI.


  Subjects and Methods Top


Laboratory animal grouping and method of killing

The rabbits (44 adult rabbits, weighing 2.0–2.5 kg, 22 males and 22 females; all the laboratory animals were provided by the Laboratory Animal Center of Shenyang Medical College) had been stored for 3 days at 25°C–27°C temperature conditions, and then they were hanged to death (A slip knot was fastened on the lower end of a nylon rope to make a slip loop,[7] and the upper end of the rope was hanging on a vertical bar. The slip loop was placed around a rabbit's neck. The rabbit died of asphyxia due to neck compression using its own weight to tighten the loop). The bodies of the dead rabbits were stored at 20°C room temperature, sealed condition, and prevented from exposure to flesh flies. The dead rabbits were randomly divided into comparison group and experimental group. The whole-body CT scans were performed on the experimental group of rabbits at different PMIs (time range, 0–129 h [mean 6 h]). The traditional anatomy was performed on a rabbit randomly selected from comparison group at each PMI. All experimental procedures were performed in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals.

The main instruments

NeuViz dual-slice spiral CT scanner (made by Neusoft Medical in China, 2 mm × 10 mm high-speed rare earth ceramic detector) is a 360° scan that could obtain two images, capable of providing a wide range of high-speed continuous spiral scan. Max Viewer (Version: 1.0.0131) is a CT image viewing software developed by Neusoft Medical. The software can be used to view and process images in various common methods and to measure a number of parameters, such as length, area, angle, and CT values.

Selection of image slices and parameter values

A continuous, thin-slice whole-body scan (0.75 mm slice thickness, 2 mm slice distance, tube voltage 120 kV, current 250 mA, time 1.0 s)[8],[9] was performed on experimental animals in a prone position with a spiral CT scanner at different time points before and after their death. The scanned CT image copies were observed and measured with Neusoft's CT image analysis software Max Viewer on a personal computer (operating system Microsoft Windows XP Professional, a desktop resolution of 1024 × 768).

Taking the selection of brain tissue CT images as an example: We chose three successive cross-section layers of the brain with largest cranial cavity areas, namely, 20 mm above the baseline level (the level of the lower portion of the third ventricle) for the study.[8],[10] We took a cross-sectional CT images, divided the image into four equal parts with two mutually perpendicular straight lines, and selected a certain area (5 mm 2) of the average CT values of the brain in each part. We took four average CT values of each cross-sectional CT images of the brain tissues, selected three cross-sections in total, a total of 12 average CT values, and took the average of them as the average CT value of brain tissues at a specific time point after death. The cranial cavity overall averages, brain tissue averages, and area ratio of brain tissues/whole cranial cavity were measured. We took CT values >0.0 HU when measuring the area of brain tissues and cranial cavity. Lung, heart, liver CT image selection and parameter value selection methods were the same as the brain tissue selection, and we measured average CT values of the heart, area ratio of heart/thoracic vertebrae;[11] average of lung tissues, area ratio of lung tissues/thoracic vertebrae;[12] and average of liver tissues, area ratio of liver tissues/lumbar vertebrae. The selection of the images of the abdominal organs should avoid interference with the ribs and the organs' structure.[13]

Traditional autopsy

After spiral CT scans at different PMIs, an animal was randomly selected from the comparison group for autopsy. The key observation of the autopsy included brain, lung, heart, liver changes which would be compared with spiral CT scan virtual autopsy. Traditional autopsy method was performed with reference to the relevant literature. The experimental procedure was photographed for future reference.

Statistical analysis

Statistical analysis was performed using SPSS1 Statistics 19.0 (SPSS, Inc., Chicago, IL, USA). A P ≤ 0.05 was considered statistically significant.


  Results Top


The computed tomography scan images of whole-body organs of rabbits within 129 h postmortem

Brain

Putrefaction area on CT images showed a low density (CT <0.0 HU), and it was a mixing area of brain tissues and putrefaction gases. The area of the brain tissues of the rabbits was basically unchanged within 0–27 h after death. The putrefaction area first appeared in the base and central regions of the skull 27 h after death. With the development of putrefaction, the contents of the putrefaction gases increased, and the CT values of these areas continued to decrease and gradually approached the CT values of gas. The gas area appeared in the parietal region of the skull 45 h after death, and thereafter, the gas area was increasing continuously. The CT scan images of the brain tissues of rabbit in 129 h after death are shown in [Figure 1].
Figure 1: The brain computed tomography images within 129 h of postmortem interval

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Heart

The area of the heart was basically unchanged from 0 to 27 h after the death of rabbit; the low-density putrefaction area appeared in the heart in succession 27 h after death, the area of the heart began to decrease; the low-density putrefaction, gas area also appeared in the central region of the heart 51 h after death; the area of the heart decreased rapidly since 63 h after death; as the time went on, the low-density putrefaction area continued to expand, and the CT images had gradually shown the remaining part of the atrial and the ventricular wall; the CT images had shown only a portion of remaining heart tissues in the 129 h after death. The CT scan images of the heart in the 129 h after the death of the rabbit are shown in [Figure 2].
Figure 2: The heart computed tomography images within 129 h of postmortem interva

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Lung

Unlike other organs, the area of the lung exhibits characteristic changes of the pulmonary window in different stages after the death of the rabbit.[9] Based on the characteristics of lung CT imaging, it can be divided into three stages: (1) during 0–33 h after death, the area of the lung was relatively unchanged; (2) during 33–87 h after death, the area of the lung decreased quickly, with the extension of PMI; at 45 h after death, the lung separated from the thorax and abdomen and was filled with gases around; (3) during 87–129 h after death, the decrease in the area of the lung was relatively stable; in this stage, the lobes and segments of the lung became blurred, the density of the pulmonary parenchyma increased was nonuniform, and the changes in the pulmonary parenchyma scattered in spots and sheets. The CT scan images of the lung 129 h after the death of the rabbit are shown in [Figure 3].
Figure 3: The lung computed tomography images within 129 h of postmortem interval87

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Liver

During 0–27 h after death, the texture of each liver lobe was uniform, there was no low-density area in the liver, and there was no significant change in the area of the liver. During 27–69 h after death, the area of the liver decreased quickly, with the extension of PMI; at 33 h after death, the liver separated from the thorax and abdomen and was filled with gases around; in this stage, the liver parenchyma area was shrinking continuously. During 69–129 h after death, the decrease in the area of the liver was relatively stable, the structure of each liver lobe became blurred, the density of the liver parenchyma increased was nonuniform, and the liver tissues scattered in spots and sheets; at 129 h after death, the CT images showed that the liver area was filled with gases, and there were only a small amount of connective tissues. The CT scan images of the liver in the 129 h after the death of the rabbit are shown in [Figure 4].
Figure 4: The liver computed tomography images within 129 h of postmortem interval

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The computed tomography parameter values of whole-body organs and the changing trends

The CT values of brain tissues of each rabbit at different PMIs were obtained with image analysis software Max Viewer [Figure 5], wherein the average CT values of the brain tissues decreased generally, and the specific changing trends were to increase first and decrease later, i.e., the high value reached 39.1 HU from the time of death to the 33 h after death, and then the average CT values decreased until 129 h after death when the average CT values of the brain tissues could not be measured; with the extension of PMI, from 39 h after death, the overall average CT values of the cranial cavity decreased gradually and came close to the CT values of gases; the area ratio of brain tissues/cranial cavity was almost unchanged within 27 h after death; from 27 h after death, the area ratio of brain tissues/cranial cavity decreased gradually and came close to “0.”
Figure 5: The trends of brain of computed tomography parameter value within 129 h of postmortem interval (a: The average brain computed tomography value, b: The overall average computed tomography value, c: Brain area/cranial cavity area)

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The CT parameter values of the heart are shown in [Figure 6]. The changing trends of average CT values of the heart tissues were roughly the same as that of the brain tissues, i.e., the average CT values increased after death, and the high value reached 55.0 HU at 39 h after death, and then the average CT values decreased; the area ratio of heart/thoracic vertebrae was basically unchanged within 27 h after death, and the area ratio of heart/thoracic vertebrae decreased gradually from the 27 h after death.
Figure 6: The trends of heart of computed tomography parameter value within 129 h of postmortem interval (a: The average heart computed tomography value, b: Heart area/thoracic cavity area)

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The CT parameter values of the lung are shown in [Figure 7]. The average CT values increased continuously from the 0 to 87 h after death and peaked with −524.2 HU at 87 h after death, and then the average CT values decreased; the area ratio of lung/thoracic vertebrae was basically unchanged within the 33 h after death; during 33–87 h after death, the area ratio of lung/thoracic vertebrae decreased rapidly and then slowed down from 87 h after death.
Figure 7: The trends of lung of computed tomography parameter value within 129 h of postmortem interval (a: The average lung computed tomography value, b: Lung area/thoracic cavity area)

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The CT parameter values of the liver are shown in [Figure 8]. The average CT values of the liver tissues gradually increased after death and peaked with 58.4 HU at 33 h after death and then decreased gradually; the area ratio of liver/lumbar vertebrae was basically unchanged within 27 h after death; during 27–69 h after death, the area ratio of liver/lumbar vertebrae gradually decreased, and the rate of decrease was relatively faster; the rate of decrease in the area ratio of liver/lumbar vertebrae slowed down after 69 h after death.
Figure 8: The trends of liver of computed tomography parameter value within 129 h of postmortem interval (a: The average liver computed tomography value b: Liver area/abdominal cavity area)

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Traditional autopsy

The traditional anatomy was performed on the brain, heart, lung, liver of the rabbits, and the changes in the organs at different intervals after death that could be seen with naked eye were consistent with the CT imaging findings.

The regression analysis of multiple parameters and postmortem interval

Using SPSS1 Statistics 19.0 for curve fitting of different organs' CT parameter values and different PMI time points, we obtained the binomial regression equation of the CT values and the related coefficient (R2) [Table 1]. After t-test, the area ratio of brain tissues/cranial cavity, area ratio of heart/thoracic vertebrae, area ratio of lung/thoracic vertebrae, area ratio of liver/lumbar vertebrae, and overall average CT values of the cranial cavity showed close correlation with PMI (P < 0.001); the average CT values of the brain tissues, overall average CT values of the cranial cavity, average CT values of the heart tissues, and the average CT values of the liver tissues all decreased with the extension of PMI, which showed strong negative correlation with PMI; while the average CT values of the lung tissues did not show any significant correlation with PMI.
Table 1: The regression analysis of different organs of computed tomography parameter value within 129h PMI

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  Discussion Top


Analysis of the parameter values of brain tissues

The average CT values of the brain tissues within 129 h after the death of rabbit showed some negative correlation with PMI. The overall changing trend was decrease, and the specific changes were to increase first and decrease later; the high value reached 39.1 HU at 33 h after death, and then the average CT values decreased until the 129 h after death when the average CT values of the brain tissues could not be measured. The analysis of the autopsy findings suggests that reaching a high value at 27 h after death was related to the parenchymal changes of the brain tissues, which may be postmortem brain tissue decay of the animal, namely, relation with neurons and glial cells swelling, karyopyknosis, Nissl degeneration, and loss of brain tissue water. Then, the decrease in the CT values may be related to brain tissue softening and liquefaction. With the progress of brain tissue softening and liquefaction, rapid bacterial propagation, and decay and degradation of brain tissues, brain cells continued to reduce, decay area continued to expand, and the CT values decreased gradually. The changing trends of overall average CT values of the cranial cavity differed from the changing trends of average CT values of the brain tissues, which is to increase first and decrease later; the overall average CT values of the cranial cavity showed no obvious changes within 57 h after death. The study suggests that the brain tissue decay, cell alteration, and brain tissue softening and liquefaction were happening at the same time and neutralized each other; the average CT values of the whole cranial cavity were relatively constant. After 57 h after death, with propagation of large amounts of putrefying bacteria, putrefaction area and putrefaction gases appeared in large number in the cranial cavity, and the overall average CT values of the cranial cavity rapidly decreased until the values tended to approach the CT values of gas. The area of brain tissues and the area ratio of brain tissues/cranial cavity showed no significant change within 33 h after death; during the 33–63 h after death, CT images showed that low-density putrefaction area and putrefaction gases started to appear in the brain tissues in the base and the central region of the skull, and the brain tissues became foaming organs in general. After 69 h postmortem, the brain tissue CT images showed nonuniformity and multicenter changes. The area ratio of brain tissues/cranial cavity decreased significantly. The analysis suggests that on the one hand, despite the brain tissue hypoxia caused by the interruption of oxygen transport in blood after death of individual rabbit, brain cells and glial cell swelling, karyopyknosis, dissolution, softening of brain tissues, however, there were no putrefaction gases appeared in the early hours after death, and the area of the brain tissues was not affected, so within 33 h postmortem, the area ratio of brain tissues/cranial cavity did not change significantly. After 69 h postmortem, the putrefying bacteria in the brain tissues increased significantly. The brain tissues were gradually decomposed by putrefying bacteria and started to disappear. It produced large amounts of putrefaction gases, and the putrefaction gases constantly replaced the brain tissues. The brain tissue CT values changed significantly shortly after the death of the rabbit and can be effectively used for early-stage PMI estimation, and the regression equation of the overall average CT values of the cranial cavity can be effectively used for advanced stage PMI estimation, and they can be used in conjunction with the parameter changes in the average CT values of the brain tissues and the overall average CT values of the cranial cavity for PMI estimation.

Analysis of the parameter values of heart

During 27 h after death, the average CT values of the heart tissues increased in the beginning. This may be caused by protein denaturation and water loss in the heart. During the subsequent putrefaction stages, the average CT values of the heart tissues decreased constantly. With reference to the traditional autopsy results, this study suggests that this is caused by the autolysis and liquefaction of the heart and the propagation of putrefying bacteria in the heart. The CT images showed low-density area in the organ; with the emergence of putrefaction gases in the organ, the density of the organ decreased rapidly and gradually approaching the CT values of gas. The area ratio of heart/thoracic vertebrae gradually decreased with the extension of PMI, and the area of heart and the area ratio of heart/thoracic vertebrae showed no significant change during 0–27 h after death; the low-density putrefaction area appeared in the central region of the heart in succession in the 27–45 h after death, and the area ratio of heart/thoracic vertebrae began to decrease gradually; after the 45 h postmortem, the area of the low-density putrefaction gas area in the central region of the heart kept increasing, and the CT images gradually showed only the remaining portion of the atria and ventricular wall, and the area ratio of heart/thoracic vertebrae decreased significantly. The analysis suggests that the decay has just begun shortly after the death of the individual, and did not produce a lot of putrefaction gases. Within 27 h after death, the area ratio of heart/thoracic vertebrae did not change significantly, then under the action of large amounts of putrefying bacteria in the blood and the chest, the heart tissues were decomposed by the putrefying bacteria and gradually disappeared. This produced large amounts of putrefaction gases, and the area of the heart decreased.

Analysis of the parameter values of lung

The statistical analysis result suggests that the correlation coefficient between average CT values of lung tissues and PMI was relatively low, the changing trends showed that the average CT values of lung tissues kept increasing after death until reaching the peak during 50–81 h postmortem, and then the average CT values gradually decreased. The analysis suggests that the increase in the average CT values of lung tissues may be due to the protein denaturation and the loss of water in the organ, coupled with the relatively abundant connective tissues of the enveloping membranes and the vasculature in the lung, and with the development of the putrefaction of the lung, the average CT values of lung tissues tended to approach the CT values of gas. In terms of the area ratio of lung/thoracic vertebrae, within 33 h after death, the texture of each lobe and segment of the lung was uniform, normal lung markings were clearly visible, the edges of the lung were close to chest wall, there was no inflating trachea in the lung, and the area ratio of lung/thoracic vertebrae did not change significantly. During 33–87 h after death, the lung separated from thorax and abdomen and was filled with gases around, the region of pulmonary parenchyma kept shrinking, the area of the lung reduced quickly, and the area ratio of lung/thoracic vertebrae decreased significantly; during 87–129 h after death, the lobes and segments of the lung were hardly distinguishable, the density of pulmonary parenchyma increased nonuniformly, there were scattered and patchy pulmonary consolidation, and the area ratio of lung/thoracic vertebrae decreased slowly. The analysis suggests that within 33 h after death, the epithelial cells of individuals' lung tissues and alveoli swelled and degenerated, the CT images did not show any putrefaction gas area, and the area of the lung did not change significantly. With the extension of PMI, large amounts of putrefying bacteria propagated, the putrefaction gases continued to increase in the chest, the catabolism of lung tissues continued under the action of putrefying cells, and the area ratio of lung/thoracic vertebrae decreased rapidly after the 39 h postmortem, and after the 87 h postmortem, the tracheas, blood vessels, and residual connective tissues of the lung were difficult to be broken down, so after the 87 h postmortem, the decrease in the area of the lung was relatively slower. The study showed that the parameter changes in the average CT values of the lung tissues cannot be used for PMI estimation.

Analysis of each parameter value changes in the liver

The average CT values of the liver tissues kept increasing after death and reached the peak during 27–39 h postmortem, and then the average CT values gradually decreased. The analysis suggests that the CT values of the liver showed increasing trend initially. This may be due to the protein denaturation and the loss of water in the liver. The putrefaction area and putrefaction gas area subsequently emerged in the liver tissues, and the CT values of the liver showed decreasing trend. With reference to the traditional autopsy results, this was caused by the liver autolysis, liver liquefaction, and large amounts of putrefying bacteria propagated in the intestines, liver, and biliary system, and the liver tissues continued to be destroyed by the putrefying bacteria, so the area of the liver kept decreasing. The study used the CT values of the liver to establish nonlinear regression equation, and this can accurately reflect the estimation of PMI from the time of death until the disappearance of the liver. Within 129 h after death, the area ratio of liver/lumbar vertebrae gradually decreased with the extension of PMI, and the statistical analysis showed that there is some negative correlation between the two. This indicates that the area ratio of liver/lumbar vertebrae gradually decreased after death and showed certain regularity. Within 27 h after death, texture of each liver lobe was uniform, there was no low-density area in the liver, the frontal edge of the liver stayed close to the abdominal wall, there were a small amount of gases between the rear edge of the liver and the rear abdominal wall, there was no inflating bile duct in the liver, and there was no significant change in the area ratio of liver/lumbar vertebrae. During 27–75 h after death, the liver separated from the thorax and abdomen and was filled with gases around, and the area ratio of liver/lumbar vertebrae significantly decreased. During 75–129 h after death, the liver lobes were hardly distinguishable, there were scattered and patchy liver tissues, and the decrease in the area ratio of liver/lumbar vertebrae was relatively slower. The analysis suggests that within 27 h after death, the liver cells were destroyed by the degeneration, necrosis, and continuous autolysis, but it did not produce large amounts of putrefaction gases, and there was not much change in the area of the liver. After the 27 h postmortem, large amounts of intestinal putrefying bacteria propagated, the putrefaction gases kept increasing in the abdomen, the catabolism of the liver continued under the influence of putrefying cells, and the area ratio of liver/lumbar vertebrae decreased. The residual connective tissues of the liver were difficult to be broken down, so after the 87 h postmortem, the decrease in the area ratio of liver/lumbar vertebrae was relatively slower.


  Conclusions Top


There was a negative correlation between the CT values of different tissues and organs and the PMI, but there were some differences between various tissues and organs. The analysis suggests that this was related to the characteristics of various tissues and organs and the different types and contents of the enzymes in the tissues and organs. The correlation coefficients between area ratio of brain tissues/cranial cavity, overall average CT values of the cranial cavity, area ratio of heart/thoracic vertebrae, area ratio of lung/thoracic vertebrae, and area ratio of liver/lumbar vertebrae were higher than the correlation coefficients between average CT values of brain tissues, average CT values of heart tissues, average CT values of liver tissues, and average CT values of lung tissues, wherein the correlation of the lung tissues was not significant and cannot be used for PMI estimation. The study also found time differences in the changes of different indicators. Some tissues and organs (such as heart and liver) showed significant changes in average CT values within 30 h after death, but some other organs did not show significant changes in the parameters of the area ratio of organs and the overall average CT values of the cranial cavity until the 27 h after death. This shows that there are certain deficiencies in using a single indicator for PMI estimation. In the future, we suggests that comprehensive analyses of various indicators of different organs could establish a diversified pattern to remedy the deficiencies and make the study of PMI estimation more scientific and enhance the operability.

This study chose rabbit as experimental subjects not human corpses, and the experimental study was carried out at fixed temperature and humidity, which is the most important element to affect postmortem changes, whereas the putrefaction of the corpses could be affected by many factors in real cases; we can add different environmental conditions in the next experiment to expand the value of the study; the methods introduced in this study are far from being used for corpses, because the CT examinations is too expensive to be used for PMI estimation; however, the experimental results are encouraging, and they laid an applied foundation for the methods to readily gain widespread recognition in forensic practice. The future study may focus on taking full advantage of radiological techniques, and more efforts should be put into the study of PMI estimation of corpses. Collecting more data and establishing a database could facilitate radiological techniques to be used in forensic pathology practice soon.

Acknowledgment

We would like to thank all staff, especially Professor Xiaodong Zhang from the Laboratory of Forensic Pathology, School of Forensic Medicine, China Criminal Police University, China.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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