Forensic imaging of projectiles using cone-beam computed tomography

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Abstract

In patients with gunshot injuries, it is easy to detect a projectile within the body due to the high-density of the object, but artefacts make it difficult to obtain information about the deformation and the exact location of the projectile in surrounding tissues. Cone-beam computed tomography (CBCT) is a new radiological imaging modality that allows radio-opaque objects to be localised and assessed in three dimensions. The full potential of the use of CBCT in forensic medicine has not yet been explored.

In this study, three different modern projectiles were fired into the heads of pig cadavers (n = 6) under standardised conditions. Tissue destruction and the location of the projectiles were analysed separately using CBCT and multi-slice computed tomography (MDCT).

The projectiles had the same kinetic energy but showed considerable differences in deformation behaviour. Within the study groups, tissue destruction was reproducible. CBCT is less severely affected by metallic artefacts than MDCT. Therefore CBCT is superior in visualising bone destruction in the immediate vicinity of the projectile and projectile deformation, whereas MDCT allows soft tissue to be evaluated in more detail.

CBCT is an improved diagnostic tool for the evaluation of gunshot injuries. In particular, it is superior to MDCT in detecting structural hard-tissue damage in the immediate vicinity of high-density metal projectiles and in identifying the precise location of a projectile in the body.

Introduction

In forensic medicine, like in other medical fields, radiological procedures are used as non-invasive tools for the evaluation of injuries. Recent years have witnessed enormous technological advances in radiological imaging [1]. Whereas in the past conventional X-rays provided only two-dimensional images of bony structures, computed tomography (CT) and magnetic resonance imaging (MRI) are today routine radiological procedures that help generate three-dimensional reconstruction images. Even commercially available personal computers can create and analyse three-dimensional models. In many cases, complex anatomical structures and pathological changes can thus be displayed more clearly than previously.

The term “virtual autopsy” is used to describe a well-established routine procedure for the documentation of fractures, injury patterns or the location of metallic foreign objects in forensic medicine [2]. When, for example, conventional autopsies cannot be performed for religious reasons or because of the presence of bacterial or viral infections, post-mortem examinations can thus be carried out without invasive investigations. In these cases, both CT and MRI are today used [3], [4]. Medical images can, however, be adversely affected by artefacts, which are caused by high-density foreign objects such as dental restorations, osteosynthesis implants or gunshot projectiles [5], [6], [7], [8].

Gunshot projectiles mainly consist of metals alloys of varying density. They can contain a variety of materials that show differences in their deformation and fragmentation behaviour. Correspondingly, two factors influencing the ballistic behaviour of a projectile are velocity and barrel length.

Whether a projectile will deform or fragment upon striking a target depends on flight velocity, rotational velocity, and material composition. Depending on the material properties of the projectile, a suitable imaging modality should be selected in order to identify the exact location of the projectile and assess the condition of surrounding anatomical structures. It is usually impossible to detect a projectile by visual inspection alone since the size of the entry wound is no larger than the diameter of the projectile and the projectile path may be altered as a result of contact with bone and other tissues. Although full metal-jacketed projectiles are often used in handguns, major efforts have been undertaken to increase the amount of energy that is imparted to the target. For this reason, especially projectiles that are fired from handguns exit the body only rarely. Metallic projectiles are radio-opaque and can thus be detected by all radiological examinations.

Cone-beam CT (CBCT) is a recently introduced imaging technique that uses an X-ray beam and a detector system that move around the part of the body under examination. The main advantage of CBCT over MDCT is that it is associated with considerably fewer metal artefacts and is thus able to localise metallic foreign objects [9]. To our knowledge, there are no studies comparing the usefulness of CBCT and MDCT in the investigation of gunshot injuries caused by different types of projectiles. The focus of our study was on imaging projectiles and projectile deformation in situ and visualising patterns of destruction caused by different projectiles.

Section snippets

Material and methods

Three distinctly different types of projectiles were used in the study.

Results

All projectiles deformed as a result of their interaction with tissues. Material composition played a key role in the degree of deformation. The reproducibility of deformation varied between projectiles. Whereas Hydra-Shok® projectiles showed major differences in deformation, Action 4 projectiles deformed in an almost identical way. The results of partial metal-jacketed projectiles lay in between the other two types of projectiles.

Hydra-Shok® projectiles mushroomed on impact along the

Discussion

In the pig model, CBCT allows patterns of gunshot injuries to be evaluated on the basis of accurate three-dimensional images that are almost unaffected by artefacts resulting from the presence of projectiles.

Virtopsy is a method that has been developed to approach forensic issues in a non-invasive manner using imaging modalities. When telemedical systems are used, true-to-scale images can be exchanged and analysed at different sites [10]. For this reason, three-dimensional imaging methods are

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