by Brendon Nafziger
, DOTmed News Associate Editor | January 11, 2011
A .30-06 round rips through a leg -- but one made of rubber, plastic and other flesh-like materials. It's actually an imaging phantom propped up against a wooden board beneath a series of targets in a leafy firing range.
The shooting was part of an experiment described in an article published online Tuesday in the journal Radiology, where researchers are hoping to use multidetector computed tomography (MDCT) scans and imaging analysis software to work up bullet trajectories or bomb locations based on gunshot or shrapnel wounds.
The researchers argue that using CT scans to analyze bullet trajectory could help scientists better understand what injuries are more likely to be fatal or lead to disabilities. Current clinical reports often don't capture trajectory damage, the researchers said.
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The analysis could also help forensic researchers determine locations of snipers, understand events at a crime scene, and even undertake data mining from battlefield injury reports to develop better protective gear for soldiers.
"Investigators want to know where the sniper was and where the bomb blast originated," said lead author Dr. Les R. Folio, with the Uniformed Services University in Bethesda, Md., in a statement. "MDCT allows us to see the path and help determine these answers."
The researchers said earlier studies have looked at using CT images to analyze ballistic wound paths, but that this is the first field test to confirm CT's ability to measure trajectory angles.
In the study, a shooter fired six rounds into two imaging dummy legs from 50 yards. The researchers then took CT scans of the two legs, and had radiologists calculate angles using a Cartesian coordinate system and also a PACS angle tool.
When matched up against results from a clinometer, an instrument that measures angles, attached to the rifle, the results were fairly accurate, the researchers said. Based on analyses with a PACS angle tool, they said they are 95 percent confident that future angle determinations made by the system won't differ from actual shooting angles by more than 4.5 degrees. Calculations based on coordinate systems were somewhat less accurate, with 95 percent confidence that future angles aren't more than 6.5 degrees off.
"Overall, calculated angles show less agreement with the actual gunshot angles when the wound path involves bone, as additional bony missiles create larger exit sites, which result in greater observer subjectivity in coordinate-based determinations," the researchers wrote.
Combining both methods, though, produced the highest accuracy: 95 percent confidence that the angles weren't off by more than 4.02 degrees.
The researchers acknowledged that the study's small size means more work is needed, and that further studies might need to simulate sniper fire from various altitudes, as well as the likely greater complexity of bullet wounds in dynamic, moving persons, rather than static dummies.
But ultimately they hope the research could lead to an "automated system for wound path localization relative to fixed anatomic landmarks and trajectory calculation, with minimal or no observer input," which could save time for radiologists and give better preoperative information to surgeons.