DOI:10.2214/AJR.07.2754
AJR 2008; 190:W106-W111
© American Roentgen Ray Society
MDCT Analysis of Projectile Injury in Forensic Investigation
H. Theodore Harcke1,2,
Angela D. Levy2,
John M. Getz3 and
Stephen R. Robinson3
1 Department of Radiologic Pathology, Armed Forces Institute of Pathology,
Washington, DC.
2 Department of Radiology, Uniformed Services University of the Health Sciences,
Bethesda, MD.
3 Office of the Armed Forces Medical Examiner, Armed Forces Institute of
Pathology, Rockville, MD.
Received June 19, 2007;
accepted after revision August 16, 2007.
The opinions or assertions contained herein are the private views of the
authors and are not to be construed as official or as reflecting the views of
the Departments of the Army, Navy, or Defense.
Address correspondence to H. T. Harcke, c/o Michelle Stofa, PO Box 269,
Wilmington, DE 19899
(howard.harcke{at}us.army.mil).
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Abstract
OBJECTIVE. This article illustrates the MDCT postmortem imaging
features that have the potential to enhance forensic investigation and
conventional autopsy.
CONCLUSION. MDCT may guide, direct, or limit forensic autopsy in
projectile injury cases, thereby eliminating the need for a complete invasive
autopsy.
Keywords: forensic autopsy • MDCT • projectile injury
Introduction
MDCT is an effective imaging technique to localize gunshot wound tracks and
aid in the forensic autopsy of gunshot wound victims
[1–3].
Projectiles include a diverse group of metallic objects such as bullets,
components of explosive devices, or secondary projectiles from explosions that
may inflict injury or cause death. In the forensic investigation of death by
suspected projectile injury, determination of the projectile's entry and exit
locations, path, and associated tissue injury is important in the
determination of the cause and manner of death
[4,
5].
The purpose of this article is to illustrate the noninvasive
characterization of projectile wounds on postmortem full-body, thin-section
MDCT images. In all cases, imaging was performed on a 16-MDCT scanner. Images
were interpreted using multiplanar 2D reconstruction, minimum intensity
projection, and 3D volume rendering to critically and accurately analyze the
3D paths and features of projectile injury.
The study was performed with the approval of the institutional review board
of the Armed Forces Institute of Pathology and was HIPAA-compliant. Total-body
MDCT scans were obtained on a LightSpeed 16 (GE Healthcare) within 2–4
days after death. Subjects were scanned at 1.25 x 0.625 mm; pitch,
0.935:1; rotation speed, 0.5 second; and table speed, 17.2 mm per rotation.
Images were viewed and measured on an Advantage Workstation, software version
4.2 (GE Healthcare), using 2D and 3D multiplanar reconstructions.
Projectile Injury
Projectile injury is classified by the location of the entrance and exit
wounds and the course of the projectile path. The projectile path is
customarily described in three directions, defining the direction of
projectile travel. The description indicates whether the projectile enters the
body from anterior or posterior, left or right, and superior or inferior. The
presence or absence of foreign material within the body (e.g., bullet,
metallic fragment, or other material) is always noted and characterized
because recovery of fragments is important for ballistics documentation.
Entrance wounds are usually smaller than exit wounds
[5]. When a bullet has passed
through bone, close examination may show beveling of the bone in the direction
of travel. Beveled edges are directed inward at the bone margin of the
entrance wound and directed outward at the exit wound
[5]. Metallic particles and
bone fracture fragments are an additional indicator of directionality because
they are usually carried along the direction of projectile travel. If a
projectile fragments, pieces of metal will be distributed along the track and
mix with bone fragments (Fig.
1A,
1B,
1C).
Wound tracks through soft tissue are characterized by gas collections or
evidence of tissue and organ damage
[3]. Postmortem gas collections
in a wound track may result from the temporary cavities created when
projectile energy is transmitted to the tissue surrounding the track. Gas may
also be introduced along the track when the projectile passes through an air-
or gas-containing organ, such as lung and bowel. Because gas readily dissects
through tissue planes, scattered gas collections may also be noted in
surrounding tissues. Generalized decomposition also produces tissue gas and
should not be confused with a wound track. A collection of blood and other
body fluids can occur in the wound track or pool away from it (Fig.
2A,
2B).
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Fig. 2A —Gunshot wound to chest. Images show evidence of tissue and
organ damage and bone interaction with bilateral pleural fluid. Axial image of
chest shows wound entrance in right chest wall (arrow). Bullet passes
through posterior mediastinum (arrowhead).
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Fig. 2B —Gunshot wound to chest. Images show evidence of tissue and
organ damage and bone interaction with bilateral pleural fluid. Axial image of
abdomen shows left lower rib fracture at site of exit (arrow).
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Penetrating Wounds
When projectiles enter the body but do not exit, forensic pathologists term
these "penetrating wounds"
[5] (Figs.
3A,
3B,
3C and
4A,
4B,
4C,
4D,
4E). The projectile can remain
intact or be fragmented within the body. Wound track direction can change
depending on the shape and kinetic energy of the projectile and its
interaction with tissue, especially bone. When interpreting postmortem CT
images, it is important to remember that a straight-line path between an
entrance wound and the postmortem position does not necessarily represent the
antemortem path of the projectile because the trajectory may have been altered
by the intervening tissues. Intermediate targets such as bone may produce a
ricochet phenomenon within the body. Moreover, organ size and shape often
change postmortem (for example, lung volume may be altered by a pneumothorax
or hemothorax caused by projectile injury)
[2,
3].
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Fig. 3C —Penetrating projectile injury of head. Sagittal oblique
reconstruction image shows wound path is determined by bone fragments along
right petrous ridge and high-attenuation hemorrhage in wound path
(arrowhead). Projectile struck petrous bone after entry and changed
direction to its final location. Note bone fragments adjacent to right petrous
bone (arrow).
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Fig. 4B —Penetrating projectile wound of head. Sagittal reconstructed
CT image shows projectile wound track passes into posterior fossa through
inferior portion of petrous ridge. Nonlinear path of projectile indicates that
it was diverted by impact on occipital bone.
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Perforating Wounds
When projectiles enter and exit the body, forensic pathologists term these
"perforating wounds"
[5] (Fig.
5A,
5B,
5C,
5D,
5E,
5F). The projectile may exit
without fragmentation, in which case there is residual material, or, similar
to the tracks of penetrating wounds, projectile fragments may be deposited
within the tissue. Analysis of postmortem CT images should always consider the
position of the body at the time of injury, especially when entry and exit
wounds do not match other points on the track, such as fractures. This should
raise suspicion that the postmortem position is significantly different from
the position of the body at the time of injury
[5] (Fig.
6A,
6B,
6C,
6D,
6E).
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Fig. 6D —Perforating gunshot wound of thorax. Three-dimensional
reconstruction image of thorax viewed from posterior shows bone fracture
defects in right sixth rib and medial margin of right scapula. Note
malalignment in autopsy position.
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Combination Wounds and Special Cases
Projectiles that break into several fragments within the body may create
secondary penetrating wounds. In such cases, a single entry wound can become a
series of penetrating wounds with retained fragments along one or more
secondary perforating wounds. One or more fragments may continue and pass
outside the body. Thus, there may be one entry site and more than one exit
site.
"Keyhole fractures" of the skull are a special type of
perforating wound in which the entry and exit are close together. These occur
when the projectile strikes the surface of the calvaria in a tangential
manner. The entry is the smaller part of the keyhole, and the exit is the
larger (Fig. 7A,
7B,
7C,
7D).
Limitations of MDCT Analysis of Projectile Injury in Forensic Investigation
Soft-tissue differentiation between organs and vascular structures is poor
on postmortem CT images because of the lack of IV contrast material.
Consequently, vascular injury is often undetected. However, the detection of
hematomas or gas or fluid collections in the course of a wound track permits
prediction of vascular injury. Postmortem angiography can augment MDCT for the
assessment of vascular integrity
[6].
Gas associated with projectile tracks is variable. The amount of gas within
the projectile path depends on the anatomic structures involved and the
ballistic characteristics of a particular projectile.
Wounds easily visible on gross inspection may be subtle or not present on
MDCT because entry and exit wound characteristics may change due to effects
such as extrinsic pressure from an adjacent body part, clothing, and dependent
postmortem positioning. In some cases, 3D surface rendering may be helpful to
show wounds not easily seen on 2D reconstructions
[2].
MDCT is typically performed with the victim in the supine position.
Projectile tracks are related to the position of the victim at the time of
lethal injury and may be difficult to appreciate in the postmortem supine
position (Fig. 6A,
6B,
6C,
6D,
6E). Specifically, the lungs,
mediastinum, and heart may be shifted significantly during or after death by
hemorrhage or pneumothorax.
Conclusions
Applying essential concepts of projectile trajectory and track analysis to
MDCT permits characterization of penetrating and perforating injuries.
Postmortem MDCT is a noninvasive technique with the potential to enhance
forensic investigation and conventional autopsy.
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Abstract
Introduction
