FORT CAMPBELL, Ky. - After a mortar exploded next to Spec. James Saylor last year in Afghanistan, he underwent a series of scans to see how the explosion affected his brain. Standard CT scans showed no obvious signs of damage, but his symptoms were impossible to ignore.

At 31, the father of two was quick to anger and had vivid nightmares and short-term memory loss. So his doctors at the Army's Fort Campbell tried a brain-imaging procedure more commonly used to study dementia and found decreased levels of blood flow in some areas of his brain.

"What's interesting here is that we are seeing things here that we can't see in their standard CT scan" or MRI, said Maj. Andrew Fong, chief of radiology at the post's Blanchfield Army Community Hospital.

The scan, called single-photon emission computerized tomography, or SPECT, produces data about the level of perfusion, or blood flow inside the brain, which is rendered in colors from red and white to blue and gray. The results helped doctors confirm their diagnosis of a brain injury and determine treatment.

Since 2000, the military estimates more than 200,000 service personnel have mild traumatic brain injuries, or concussions, which have become the signature wound from extended guerrilla wars. But the military is finding these wounds created by improvised explosive devices can be as hard to catch as they are to treat.

While normal CT scans can find contusions and brain bruising, more sophisticated technology is needed to help radiologists and neurologists determine more subtle changes to the brain, Fong said.

Fong said that while the SPECT scan had been used to study dementia and Alzheimer's, it was underused in the military. Fort Campbell is one of only two military installations to use the scan to study traumatic head injuries and concussions caused by war, he said.

In the scans, colors correspond to the level of blood flow, with white and red showing areas of high perfusion and darker areas showing low perfusion. Some more active areas of the brain naturally are "hotter" than other parts and age can also slow down blood flow, Fong said.

"When you are younger, like a lot of our soldiers are, you expect a lot of perfusion - a lot of activity because their brains are fresh," he said.

But as Fong started looking at soldiers who were coming back from war with brain injuries, he saw large areas of their brains that were less active than normal.

Pointing to a dark area in one image, he notes doctors have been seeing several soldiers who have less blood flow in the temporal lobes. Once he started discussing the scans with David Twillie, director of Fort Campbell's brain-injury center, they wondered whether the scans were showing them the effects of a blast injury. The temporal lobes sit behind the eye sockets on either side of the brain and are in the path of the shock waves made by blasts, Fong said.

In addition to his brain injury, Saylor was also diagnosed with post-traumatic stress disorder. He has been taking medications for his nightmares, which were at times vivid enough that his wife, Tiffany, had to wake him up because he was fighting in his sleep.

"You relive what you've been through, over and over," he said. "You see other things that could have happened. It's a constant battle."