Go Go

Figure 14.8 Comparison of predicted times determined by 1H-MR spectroscopy versus times based on forensic evidence for the four human cases. Predicted PMIs are shown with an error range of ±2 standard deviations, while identity (predicted = forensic) is represented as a straight line. Reproduced with permission from Scheurer et al. (2005)

Figure 14.8 Comparison of predicted times determined by 1H-MR spectroscopy versus times based on forensic evidence for the four human cases. Predicted PMIs are shown with an error range of ±2 standard deviations, while identity (predicted = forensic) is represented as a straight line. Reproduced with permission from Scheurer et al. (2005)

ing body temperature and decomposition is undisputed. However, in order to take these factors into account, it is necessary to consider additional information, e.g. from weather reports, etc. In forensic practice, the influence of temperature has been studied in detail (Friedrich, 1986; Althaus and Henssge, 1999; Al-Alousi et al., 2001; Campobasso et al., 2001), particularly the effect of temperature on specific processes, e.g. the degradation of muscle tissue, the increase of potassium in the vitreous humor, etc. Many authors also studied the effect of ventilation, humidity and clothing (Mann et al., 1990; Campobasso et al., 2001; Henssge 2002) and tried to classify the extent of the influence of these factors on the decomposition rate. Experience shows that the overall decomposition rate in tissues of human bodies stored at 4°C is significantly slower than at 20°C. However, since the changes observed by 1H-MRS include two different mechanisms, i.e., autolysis and heterolysis, it is not at all obvious that the time courses of the metabolites from the two processes are affected in the same way by variations of the temperature. This is at the same time a complication as well as a chance. If the two processes proceed independently, the interpretation of the calibration curves would get much more complicated and, in turn, independent calibration curves for autolysis and heterolysis would contain additional information that could, in principle, be used to estimate the influence of the ambient temperature. In an ongoing study the influence of temperature on brain decomposition tissue is investigated with sheep heads in order to extend the sheep model.

Although it is generally accepted that internal factors may change the progress of decomposition, the influence of most of them is not well documented. Among them are antemortem diseases, which in some cases may even provoke death, such as diabetes or alcoholism. In contrast, the influences of drugs such as antibiotics have been proven to be insignificant for the later postmortem period since they are degraded within a short time (Daldrup et al., 1982). The influence of other drugs is still unclear (Wagner, 1967). The cause of death can promote decomposition by facilitating bacterial colonization, i.e. in the form of injuries of the skin or enhanced blood fluidity in asphyxia. Systematic studies of the influence of the different factors are difficult, because they interfere and can hardly be standardized.

While it is obvious that calibration curves cannot be obtained with human cases, it is nevertheless necessary to validate the curves obtained from the sheep model with human cases at specific points of time. As described in the previous section, it is unlikely that the time of death can be determined exactly in a body that is only found several days or weeks after death. A delay in locating a human body is often due to limited or non-existent social contacts, which makes an exact determination of the PMI very difficult. Since restriction of the PMI is often based on criminal evidence that is not immediately available when the body is found, bodies have to be included in a study with the hope that a further restriction of the time span is possible. To date, 40 human bodies from the Institute of Forensic Medicine have been investigated by means of in situ 1H-MRS of the brain - in many of these cases it is not possible to restrict the possible PMI to a short period in time, therefore it is necessary to acquire a larger number of bodies in future.

Despite the fact that many factors such as ambient temperature influence the results and that a gold standard is almost missing in human cases, the simple concept of a non-invasive and simultaneous observation of multiple metabolites during decomposition of the brain is promising. Since MRI is increasingly used to examine bodies in forensic investigations (Thali et al., 2003; Yen et al., 2004), the additional effort and expense to obtain a 1H-MR spectrum of the brain are acceptable and can provide crucial information on the time of death, particularly during the later postmortem phase.

Was this article helpful?

0 0

Post a comment