A review of visualization techniques of post-mortem computed tomography data for forensic death investigations

Abstract

Postmortem computed tomography (PMCT) is a standard image modality used in forensic death investigations. Case- and audience-specific visualizations are vital for identifying relevant findings and communicating them appropriately. Different data types and visualization methods exist in 2D and 3D, and all of these types have specific applications. 2D visualizations are more suited for the radiological assessment of PMCT data because they allow the depiction of subtle details. 3D visualizations are better suited for creating visualizations for medical laypersons, such as state attorneys, because they maintain the anatomical context. Visualizations can be refined by using additional techniques, such as annotation or layering. Specialized methods such as 3D printing and virtual and augmented reality often require data conversion. The resulting data can also be used to combine PMCT data with other 3D data such as crime scene laser scans to create crime scene reconstructions. Knowledge of these techniques is essential for the successful handling of PMCT data in a forensic setting. In this review, we present an overview of current visualization techniques for PMCT.

Keywords: 3D printing; Postmortem computed tomography; Reporting; Segmentation; Virtual reality; Visualization.

Fig. 1

Polygon model describing the surface of an anthropologist’s skull, based on data extracted from a CT scan. Polygon meshes consist of points called vertexes that are interconnected by their edges to form polygons or faces

Fig. 2

PMCT scan of the neck, visualized in different windows. (a) soft tissue window; (b) lung window; (c) bone window; (d) brain window. Note that the material obstructing the airways is only visible in image b, the lung window, and does not appear in any of the other images

Fig. 3

MPR of a suicidal gunshot injury with the entry wound on the right and the exit wound on the left side. The reconstruction follows the path of the bullet through the brain. (a) coronal view; (b) axial view

Fig. 4

Different types of complex 2D reconstructions. a Curved MPR of an individual’s dentition, simulating an orthopantomogram that can be compared to antemortem images. b Rib unfolding that can be used in the rapid assessment of multiple rib fractures (c). Skull unfolding showing surgical plates and screws after surgical intervention

Fig. 5

Different volume visualizations of the same PMCT dataset. a Averaging visually mimics the appearance of a plain radiograph. b MIP highlighting structures with high x-ray density such as bone. The high-density material visible in this image is debris that is located underneath the body. c MinIP visualizing the gas distribution inside the body and excluding the air surrounding the body

Fig. 6

VRT of a suicidal shotgun injury demonstrating visualization using different transfer functions. (a) Surface visualization. (b) Bone visualization. (c) Visualization of radio dense material in blue

Fig. 7

Cinematic rendering of a suicidal gunshot injury to the head. The rendering demonstrates increased perceived realism through the physically correct calculation of optical effects such as shadowing. a View from the left showing the exit wound. b Frontal view with skull fracture. c View from the right with entry wound

Fig. 8

Segmented data. a Sagittal view of a PMCT dataset. b Segmented spine. Each vertebra, disc, and the sacrum has been semiautomatically segmented and color-coded

Fig. 9

Visualization of drug containers on PMCT in a case of body backing. VRT of soft tissue and bone was mixed with a polygon rendering resulting from segmentation of the drug containers

Fig. 10

Visualization of a hanging using multiple layered cinematic renderings (bone, muscle body, and surface). Using this method, the bony structures of the neck and the rope can be visualized at the same time despite the fact that the rope has a Hounsfield density similar to that of the soft tissue. Painted transparencies on different layers allow exposure of underlying structures such as the hyoid bone

Fig. 11

Annotated images. a Visualization of hemothorax and tension pneumothorax by color-coding of different structures. Heart (green), lungs (blue), and blood (red). b Combined VRT and polygon rendering displaying dislodged bone fragments. Additional annotations highlight the bullet path as well as a smaller projectile fragment. c Cinematic rendering of fractures of the ribs and clavicular bone, annotated using different-colored arrows

Fig. 12

3D-printed skull extracted from a CT scan using FDM printing