It happened in a fraction of a second.
On Jan. 29, 2006, a roadside bomb detonated next to the vehicle carrying ABC News anchor Bob Woodruff in Iraq. The shock wave from the explosion propelled jagged shrapnel and rock, traveling at a deadly velocity, toward his head.
In less time than it takes to read this sentence, his brain was forever changed.
Woodruff awoke more than a month later, only to begin a long road to recovery. His journey is one that is shared by an estimated 80,000 to 90,000 Americans each year who suffer traumatic brain injury, or TBI.
While at least some degree of recovery is possible for many of these patients, the progress back to the people they once were is gradual and uncertain.
And many do not make it back.
Mark Ashley is president of the Centre for Neuro Skills and is on the board of directors of the Brain Injury Association of America. He says the way that a traumatic brain injury progresses relates to the brain's layered structure.
Running through these layers is an intricate system of delicate nerves and blood vessels, all crucial to the brain's proper functioning.
When the head is hit with a great deal of force, Ashley says, "Each of the different layers -- because they are of different densities and different weights -- travel at different speeds."
Thus, Ashley says that in many ways, the effect of such a force can be compared to that seen in a city during an earthquake -- except that instead of pipes and underground cables, the connections being sheared are the fragile connections of nerves and vessels between the layers of the brain.
Most vulnerable to these forces is the network of tissues that connect the right side of the brain to the left -- what Ashley calls the "wires" that allow the connection of one part of the brain to the other.
When a trauma, such as that created by an explosion, disrupts this living switchboard, the effects on the brain can be drastic.
"As these wires become detached, now we end up with widespread damage throughout the brain," Ashley said.
In the initial days and weeks after a traumatic brain injury, the first hurdle a patient must face is the simple act of survival.
While a patient with a brain injury, such as a stroke, may be medically stable within 24 hours to 48 hours, Ashley says, a person with moderate to severe brain injuries "may be critically ill for days or weeks."
Kit Callahan has a firsthand familiarity with such an experience.
Callahan sustained a traumatic brain injury when he was assaulted in 1993. The assault left him with massive head injuries, and he remained in a coma for weeks.
When he finally awoke, he faced a new challenge: learning how to communicate and move his body now that his brain had suffered irreparable damage.
"The hardest part for me was just learning to walk and talk again," he said. "My speech is obviously no longer what it used to be."
"If you had known me before, you would have known I have a great singing voice," he said.
The comment is a self-effacing joke -- a feat requiring brainpower that would have been impossible to muster during the early phases of his recovery, when even simple communication was impossible.
"Saving a patient's life is only just the beginning," said psychiatrist Gregory O'Shanick, medical director of the Center for Neurorehabilitation Services in Midlothian, Va.
The good news, O'Shanick says, is that if a patient begins to recover, the rate of recovery seen in the months after injury is often rapid.
"Think about the injury as being your birth," he said. "If you look at the development from infancy as kind of a backdrop, the first part of recovery in that first six months is going to be meteoric."
In this phase, with any luck, the patient regains the ability to feed himself or herself, walk with assistance, and perform other basic tasks. Some gross motor skills and basic movements may also return.
To family members, the progress may be heartening, but this rapid rate of improvement, in most cases, does not last.
About six months after many traumatic brain injuries occur, patients begin to experience a slowdown in improvements.
Rehabilitation at this phase normally involves developing safety awareness and balance, cognitive rehabilitation to improve memory, and dealing with impulsivity and multitasking.
Patients may also be able to refine their motor skills, develop more sophisticated cognitive skills, articulate more effectively, and control their impulses.
However, constant care is still needed.
"When you take a look at recovery of function, you have to look at it case by case," Ashley said. "Approximately 5 [percent] to 20 percent of individuals who have sustained a mild TBI or concussion will have one or more symptoms that last a year or longer."
"These patients are entering a lifelong period of attention, concentration, memory, fatigue, cognitive and emotional disabilities."
After the first few years following injury, the improvement curve in most cases becomes completely flat; patients rarely improve past this point.
"What you see as problems at two years after injury are generally seen as permanent," O'Shanick said.
However, a few patients can recover from their injuries enough to continue their lives to a certain degree.
Abigail Baglione, a senior at NYU, was out with friends on the night of Sept. 20, 2000. It was a typical night on the town until the car they were riding in was broadsided by another vehicle.
Baglione, who was sitting in the front passenger-side seat, received the brunt of the impact.
The brain injury she sustained from the crash impaired her ability to think and learn.
"Awareness and realization takes a long time," she said. "It was really hard, and I went through periods of depression."
Yet, the damage to her brain was limited in severity. Perhaps most important, her sense of motivation, which many TBI patients lose after their injuries, was not affected.
"I really, really wanted to go back to school, so I made that happen," she said.
Her return to NYU was a challenge. Baglione was in her senior year when the accident occurred; finishing her final two semesters took two extra years.
Nonetheless, she graduated in May 2003, and is currently at NYU working toward her master's degree in social work.
She says she still suffers from fatigue and takes stimulants to stay awake and focus. She also says that she learns more slowly now, and that her organization skills are not as keen as they used to be.
But she realizes her condition could have been much worse.
"I am really lucky," she said.
Statistics suggest Baglione is fortunate, indeed.
"The vast majority of individuals who have had a traumatic brain injury, five to seven years post-injury, will not have returned to work," Ashley said.
Some patients, he adds, may never recover past the minimally conscious state they entered after their injury.
But for "success stories," such as Baglione's, a question remains: Can patients recover completely?
"I've never seen that happen in 26 years of treating 11,000 patients," O'Shanick said. "Can they get close? Yes. But do they have to make concessions? Yes."
Sometimes, though, even small steps toward recovery can make a big difference to loved ones.
On a Monday morning in March, Woodruff's wife, Lee, pulled back the curtain in his room to find him fully conscious for the first time in a long time. He was sitting up in bed with bright eyes.
He turned to his wife and said, "Sweetie, where have you been?"
As Woodruff continued his recovery from this point, he began a life forever changed by his injury, but not without hope.
"It's about regaining cognitive skills, but also about managing loss, as well as acceptance and finding your own new place in the world," said Susan Connors, president and CEO of the Brain Injury Association of America.
"My hope is that others who sustain brain injuries show the same kind of courage that Bob and the Woodruff family have."