Ballistic Injury Imaging: The Basics

Abstract

Purpose

As of 2007, there were estimated to be at least 750 million firearms in worldwide circulation, of which 650 million of them were owned by civilians (Weiss et al. in Severe lead toxicity attributed to bullet fragments retained in soft tissue. BMJ Case Reports, 2017). Of these, approximately 270 million are in the United States, equating to 84 guns per 100 Americans [based on 2016 population statistics (assuming the number of firearms remained stable over the intervening 9 years)] and resulting in 84 997 nonfatal injuries and 36 252 fatalities in the United States in 2015. With statistics like these, it stands to reason that victims of gunshot wounds (GSW) will be imaged by most radiologists at least once in their careers. This article seeks to increase radiologists’ knowledge of the pathophysiology of GSW and will review the mechanism of ballistic injury and relate these to commonly encountered imaging findings.

Important Points

Ballistic injuries are a combination of the direct injury caused by the bullet along its path through the tissues and the shockwave created around that path as the bullet expends its energy. CT is the gold standard in ballistic injury assessment. MRI is not contraindicated in patients with retained ballistic fragments, but should be used with caution. The number of entry/exit wound and the number of retained ballistic fragments should be an even number, or there is a missing surface wound or a missing bullet. Retained lead in joints can result in plumbism and arthropathy.

Summary

As most radiologists will encounter a ballistic injury in the course of their careers, an understanding of this unique mechanism of injury and its complications will aid in both imaging interpretation and patient care.

Appendix 1

Head and cervical spine protocol
Oral contrast	None
IV contrast	None
Start location	Series (1) Foramen magnum Series (2) Foramen magnum
End location	Series (1) Vertex Series (2) T2
Interval	Series (1a) Axial 2.5 mm (for post fossa) then Axial 5 mm (1b) Axial 2.5 mm Series (2a) Helical 0.635 mm × 0.625 mm (2b) Helical 2.5 mm × 1.25 mm
SFOV	Series (1) Head Series (2) Small Body
DFOV	25 cm
Detector width	20 mm
kV	Series (1)140 kVp from foramen magnum to petrous ridge 120 kVp from petrous ridge to vertex Series (2) 140 kVp
mA	Series (1)335 mA from posterior arch of C1 to petrous ridge 300 from petrous ridge to vertex Series (2) auto mA
Tube rotation	Series (1) 1.0 s Series (2) 0.8 s
Scan delay	None
Algorithm	Standard and bone
Reformats:	Coronal and Sagittal 2.0 mm × 1.0 mm c-spine on Bone and Standard

Chest, abdomen and pelvis protocol
Oral contrast	None
IV contrast	100cc @ 3.0 cc/s
Start location	Series (1a) Supraclavicular fossa Recon (2a) Lung Apex Series (1b) Dome of diaphragm
End location	Series (1a) mid kidney Recon (2a) Costal phrenic angles Series (1b) Ischial tuberosities
Interval	Series (1a) 0.625 mm × 0.625 mm Recon (2a) 2.5 mm × 1.25 mm Series (1b) 0.625 mm × 0.625 mm
SFOV	Large
DFOV	Series (1a) (1c) and (2) Smallest possible DFOV that will include skin all the way around at largest part of area being scanned Series (1b) Smallest DFOV that includes everything inside ribs
Detector width	40 mm
kV	120
mA	Auto
Tube rotation	0.6 sec
Scan delay	Series (1) smart prep Series (2) 70 seconds
Algorithm	Series (1a) Standard recon (2) lung Series 1b) Standard
Reformats	Series (1a) Axial (2.5 mm × 1.2), Coronal (3 × 3) and Sagittal (3 × 3), Oblique (2 × 1) through the Aortic Arch Series 1a) Axial (2.5 mm × 1.2), Coronal (3 × 3) and Sagittal (3 × 3)