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Essentials of forensic post-mortem MR imaging in adults - PubMed

Review

Essentials of forensic post-mortem MR imaging in adults

T D Ruder et al. Br J Radiol. 2014 Apr.

Abstract

Post-mortem MR (PMMR) imaging is a powerful diagnostic tool with a wide scope in forensic radiology. In the past 20 years, PMMR has been used as both an adjunct and an alternative to autopsy. The role of PMMR in forensic death investigations largely depends on the rules and habits of local jurisdictions, availability of experts, financial resources, and individual case circumstances. PMMR images are affected by post-mortem changes, including position-dependent sedimentation, variable body temperature and decomposition. Investigators must be familiar with the appearance of normal findings on PMMR to distinguish them from disease or injury. Coronal whole-body images provide a comprehensive overview. Notably, short tau inversion-recovery (STIR) images enable investigators to screen for pathological fluid accumulation, to which we refer as "forensic sentinel sign". If scan time is short, subsequent PMMR imaging may be focussed on regions with a positive forensic sentinel sign. PMMR offers excellent anatomical detail and is especially useful to visualize pathologies of the brain, heart, subcutaneous fat tissue and abdominal organs. PMMR may also be used to document skeletal injury. Cardiovascular imaging is a core area of PMMR imaging and growing evidence indicates that PMMR is able to detect ischaemic injury at an earlier stage than traditional autopsy and routine histology. The aim of this review is to present an overview of normal findings on forensic PMMR, provide general advice on the application of PMMR and summarise the current literature on PMMR imaging of the head and neck, cardiovascular system, abdomen and musculoskeletal system.

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Figures

Figure 1.
Figure 1.

Comparison between antemortem and post-mortem MR images: antemortem coronal whole-body T1 weighted (a) and short tau inversion–recovery (STIR) (b) images of an elderly patient suffering from aneurysm of the ascending aorta (not visualized on this image). (c, d) Post-mortem coronal whole-body T1 weighted (c) and STIR (d) images of the same patient after fatal rupture of the aneurysm with hemopericardium and pulmonary fluid accumulation. Note the absence of motion artefacts and the anatomical detail on the post-mortem images in comparison to the ante-mortem images.

Figure 2.
Figure 2.

Position-dependent sedimentation on axial T2 weighted post-mortem MR images: (a) intravascular sedimentation typically exhibits fluid–fluid levels (arrows). Cellular components of blood settle in the dependent areas as a dark hypointense layer, whereas bright hyperintense fluid components are seen in a non-dependent position. (b) Fluid–fluid levels (arrows) may be disturbed by the presence of post-mortem clots (area within the dotted lines in the right and left atrium). (c) Position-dependent sedimentation (arrows) is also visible in the lungs (area within the dotted lines), but the differentiation between sedimentation and other coexisting fluid accumulations, such as pulmonary oedema, is challenging.

Figure 3.
Figure 3.

Temperature dependence of post-mortem MR images: coronal whole-body T1 weighted images of two different cadavers (a) with body temperature of 24 °C and (b) with a body temperature of 4 °C. On T1 weighted images, image contrast deteriorates at body temperatures of 10 °C or lower.

Figure 4.
Figure 4.

Post-mortem gas (a, b) coronal whole-body T1 weighted post-mortem MR images at two different levels in a case with significant intracardiac (a, arrow), intravascular (b, arrows), intrahepatic (circled by dotted line) and intestinal gas (arrowheads).

Figure 5.
Figure 5.

Metal artefacts on post-mortem MR. (a) Axial CT image at the level of the base of the skull with a metallic hair clip (circled by the white dotted line) behind the right ear. (b) Detailed view of a coronal whole-body short tau inversion–recovery image of the same case with extensive signal loss and distortion (circled by the white line) on the right side of the head and neck induced by the same hair clip. (c) Axial T2 weighted PMMR image of the skull with a small metal artefact in the left frontal lobe (arrow) caused by a non-ferromagnetic ballistic projectile.

Figure 6.
Figure 6.

The forensic sentinel sign: coronal whole-body short tau inversion–recovery (STIR) image in a case of blunt force trauma featuring several pathological fluid accumulations, which are also referred to as “forensic sentinel sign” (circled by white dotted lines). Fluid accumulations are highly conspicuous on STIR sequences and may be used as an indicator of pathology.

Figure 7.
Figure 7.

Post-mortem imaging of the brain: axial T1 weighted post-mortem MR image of the brain with typical hyperintensity of the basal ganglia.

Figure 8.
Figure 8.

Diffusion tensor imaging (DTI) fibre tractography provides an effective means to visualize brain injury. (a) Axial T2 weighted post-mortem MR (PMMR) image of a brain with acute hypertensive intracranial haemorrhage (note fluid–fluid level in the right posterior ventricle). (b) Same image complemented by DTI fibre tractography to visualize the effect of the massive cerebral haemorrhage with displacement and disruption of fibre tracts. (c) Axial T2 weighted PMMR image of a brain with a gunshot injury. (d) Same image complemented by DTI fibre tractography illustrating the extensive destructive power of a ballistic projectile.

Figure 9.
Figure 9.

Post-mortem images of the decomposed brain: comparison between an axial post-mortem CT (PMCT) image (a) and axial T1 weighted (b) and T2 weighted (c) PMMR images of a brain in a moderate stage of decomposition. PMMR displays anatomical details and relationships well into the process of decomposition and with tissue contrast that is superior to PMCT.

Figure 10.
Figure 10.

Cardiac post-mortem MR (PMMR) image of an acute myocardial infarction of the posterior wall: short axis T2 weighted PMMR image of the heart (near the apex). The post-mortem imaging findings of acute myocardial infarction (circled by white dotted line) are comparable to those in clinical cardiac MR and consist of focal necrosis surrounded by perifocal myocardial oedema with increased signal intensity on T2 weighted images.

Figure 11.
Figure 11.

Post-mortem MR (PMMR) angiography: left column features non-contrast axial T1 weighted images of the abdomen (a), the aortic arch (b) and the pulmonary arteries (c), the right column features post-contrast T1 weighted fat-saturated images of the same levels. (a) Note the striking expansion of the inferior cava vein on the post-contrast image. (b) PMMR angiography clearly displays the intimal rupture (arrow) in this case of aortic dissection. (c) Position-dependent sedimentation of contrast medium is a current limitation of PMMR angiography. Note contrast-fluid levels in both ascending and descending aorta (arrows). This artefact is also visible (but to a lesser degree) in the inferior cava vein in (a).

Figure 12.
Figure 12.

Assessment of coronary artery disease on non-contrast post-mortem MR: three sets of T2 weighted images of a heart with full field images and detailed images. Chemical shift artefacts (circled by continuous white line on all images) appear as light and dark signals on opposite sides of vascular structures within the epicardial fat, and their presence indicates vessel patency. These artefacts must not be confused with position-dependent sedimentation. Chemical shift artefacts are not present if the vascular lumen is filled by erythrocytes (a, dotted line) or in the presence of arteriosclerotic plaques, which may be visible as paired dark bands (c, dotted line).

Figure 13.
Figure 13.

Assessment of heart weight: four-chamber view post-mortem T2 weighted MR image and short-axis view topogram of the heart. Heart weight can be estimated by single area measurements on four-chamber view of the heart. The circumferential area (in squared centimetres) of the left ventricle at mid-level corresponds to approximately one-tenth of the heart weight, as measured at autopsy (caveat: area measurements on the figure are in squared millimetres).

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