Modern diagnostic imagining techniques are gaining popularity in forensic medicine. Denmark has been involved in the development of this use of imaging techniques from the beginning. The Institute of Forensic Medicine at the University of Southern Denmark acquired a helical computed tomography (CT) scanner in 2006. This thesis presents our research on post-mortem CT (PMCT) and addresses the following research questions: 1. In how many cases can the cause of death be established by PMCT, and what characterises these cases? 2. What is the inter-method variation between autopsy and PMCT with regard to disease and injury diagnoses? 3. Can PMCT be used as a screening tool for selecting cases for autopsy, and can PMCT in some cases substitute for autopsy? 4. What is the inter-observer variation in PMCT? Who should evaluate the images? 5. How much new information is obtained by the histological examination of tissue samples? 6. Can PMCT be used for Abbreviated Injury Scale (AIS) scoring and Injury Severity Scoring (ISS) of traffic fatalities? 7. How can coronary PMCT angiography (PMCTA) be used for optimising clinical CT of the coronary arteries? 8. How can PMCT contribute to forensic autopsies? MATERIALS AND METHODS: This thesis investigated 900 forensic cases that were CT-scanned and autopsied at the Institute of Forensic Medicine, University of Southern Denmark, from 2006-2011. The scanner was a Siemens Somatom Spirit dual-slice CT-scanner with a Siemens Syngo MultiModality workstation. Contrast enhancement was not used. Autopsies were performed according to the Danish government's official guidelines. PMCT and autopsy findings were interpreted independent of each other. Diagnoses, including the cause of death and histology findings, were registered in a computer database (SPSS) together with information about the deceased and the case. We also estimated whether an autopsy could have been omitted according to a set of predetermined criteria. RESULTS: 1. Cause of death: Agreement about the cause of death was found in 66% of cases. No cause of death could be found by PMCT in 45% of cases, compared with only 15% of cases by autopsy. The agreement between PMCT and autopsy was highest in cases of accidents (85%) and lowest in cases of natural deaths (48%). 2. Inter-method agreement: A total of 70% of non-injury diagnoses and 65% of injury diagnoses were obtained by both autopsy and PMCT. PMCT was unable to detect some important non-injury diagnoses (coronary stenosis, coronary thrombosis, acute myocardial infarction, fibrotic myocardial scar, pulmonary embolism, oesophageal varices, and non-perforated gastrointestinal ulcerations). PMCT was good at detecting major haemorrhages, air and fluid collections, fatty liver, hyper- and hypotrophy, neoplasms, cysts, gallstones, kidney stones, aneurysms, and cerebral haemorrhages. PMCT was superior to autopsy in detecting fractures in the facial skeleton, spine, and extremities, but it was less reliable in detecting injuries in the inner organs, small haematomas, and aortic transections. 3. PMCT as a screening tool: It was estimated that PMCT could substitute for autopsy in at least 15% of cases, but in 6% of these cases, an important autopsy finding would be missed. There were more accidents and fewer natural deaths among the cases where an autopsy could be omitted. 4. Inter-observer variation: The inter-observer variation of PMCT injury diagnoses between a forensic pathologist and a radiologist was evaluated in a study of 67 traffic fatality victims with 994 AIS injury diagnoses. The study showed a substantial inter-observer agreement (kappa=0.65). The radiologist diagnosed more injuries than the pathologist, especially injuries in the spine and face. The radiologist diagnosed more injuries in the skeletal system, and the pathologist diagnosed more injuries in the organs and soft tissues. The difference between the two observers was smallest for lesions with a high AIS severity score. 5. Importance of histology: The histological examination confirmed the autopsy findings in 59% of all cases. Important new information was obtained in 23% of cases, and some, but less important, new information was obtained in 15% of cases. There were significantly fewer important microscopic findings (7%) in cases where it had been estimated that an autopsy could be substituted by PMCT. 6. PMCT used to assess the AIS score and ISS: This question was investigated in a study of 52 traffic fatalities. On average, there was 94% agreement between PMCT and autopsy in the detection of lesions, with kappa-values varying from 0.39 to 1.00 among the different AIS anatomical regions. When different severity scores were obtained, PMCT detected more lesions with a high severity score in the facial skeleton, pelvis, and extremities, whereas autopsy detected more lesions with high scores in soft tissues, the cranium, and ribs. In 85% of these traffic fatalities, there was no or moderate variation in the ISS (kappa=0.53). When the difference was higher, it was usually because an aortic rupture had been overlooked by PMCT. 7. Post-mortem coronary angiography: A new method was presented in which an autopsy heart was investigated with optical coherence tomography (OCT) and scanned in a chest phantom with dual-energy CT. A contrast agent that solidified after cooling was injected into the coronary arteries. The OCT and CT images were compared with their corresponding histological sections. A procedure for ensuring the correct alignment of the images was also developed. 8. Contribution of PMCT to forensic autopsy: PMCT findings in cases of fire, identifications, traffic fatalities, drowning, bolus deaths, and homicides are presented. Three case studies are summarised: detection of tablet residues in the stomach, detection of a congenital displacement of the second cervical vertebra in a newborn, and an investigation of the sacral bone from the medieval Danish King Canute the Saint. DISCUSSION: 1. Cause of death: Unenhanced PMCT could not detect several important natural causes of death, including many cardiovascular diseases, but could identify the cause of death in many cases where death was caused by injury, most likely because fractures, large haemorrhages, and pneumothoraces could be detected by PMCT relatively easily and because many deaths were caused by severe, and therefore easily identifiable, injuries. 2. Inter-method variation: PMCT was superior to autopsy in some cases, such as in diagnosing fractures, investigating areas not dissected in the autopsy, and detecting pneumothorax and other pathological gas collections, but PMCT also had some significant weaknesses, especially in the diagnosis of pathological lesions (mainly cardiovascular diseases). Several researchers have suggested strategies to overcome these diagnostic limitations, including the use of CT-guided biopsy and post-mortem angiography. 3. PMCT as a screening tool: It was possible to select some cases in which PMCT could replace autopsy. Our study included only cases selected for autopsy and should be supplemented with a study on cases not selected for autopsy. In some cases autopsy must always be performed, e.g., if an extensive histological investigation is needed or in automobile drivers to exclude natural diseases that may have caused the accident. Autopsy is mandatory by Danish law if homicide is suspected. 4. Inter-observer variation: The inter-observer variation was low, but the radiologist diagnosed more injuries than the pathologist. It is recommended that the pathologist consult a radiologist for the evaluation of CT images. 5. Importance of histology: The importance of histology and the possibility to supplement PMCT with needle biopsies were discussed. 6. PMCT used for AIS scoring and for assessment of the ISS: We found a high correlation between AIS scores obtained by autopsy and PMCT. Autopsy was best for AIS scoring of soft tissues, the cranium, and ribs, while PMCT was best for AIS scoring of the facial skeleton, pelvis, and extremities. There was moderate agreement between ISS obtained with autopsy and PMCT. Rupture of the aorta was often overlooked by PMCT, resulting in ISSs that were too low. A combination of autopsy and PMCT provided the most accurate information. 7. Post-mortem coronary angiography: The method presented can be used to determine whether CT evaluation of the coronary arteries with plaque characterisation is possible in preparation for a clinical study. 8. The contribution of PMCT to forensic autopsy: PMCT permits investigation of anatomic regions that are not routinely dissected by autopsy and depicts the anatomy in situ. PMCT provides digital documentation that is easily stored and transmitted, thereby facilitating audit and review by others, and provides images that are more aesthetically suited for court presentation than autopsy photographs. The importance of PMCT in gunshot cases, identifications, stab wounds, strangulation, drowning, intoxications, fire deaths, and pathological gas collections was discussed. The CT investigation of the bones belonging to King Canute the Saint was discussed.