Diffusion tensor imaging (DTI), which reveals the location of the delicate neural fibers that transmit signals in the brain, is providing insight into how the living brain shares information.
While magnetic resonance imaging (MRI) produces vivid pictures of large brain structures and functional magnetic resonance imaging (fMRI) reveals which areas are most active at a given moment, DTI reveals how the structures of the living brain communicate, a process that produces what we experience as consciousness.
“DTI is the best way we have so far to look at the wiring of the brain—at the connections among neurons—noninvasively,” says Gregory Sorensen, an associate professor of radiology at Harvard Medical School.
DTI works by monitoring the diffusion of water in the brain. Normally, water molecules diffuse randomly. When they do not, they must be bumping into something, such as the myelin-coated axons that transmit signals in the brain and spinal cord. By monitoring this nonrandom movement, DTI infers the location of those fibers and manufactures vivid images that depict their path.
From Strokes to Schizophrenia
By creating roadmaps of the brain’s information highways, DTI provides insight about strokes, tumors, and traumatic brain injury.
“DTI can show the effect of a stroke much sooner than other types of nuclear magnetic resonance imaging,” says Van Wedeen, also an associate professor of radiology at Harvard. “It can show which tissue is likely to die without prompt intervention. It provides a marker for how bad the stroke is, and it’s a hugely valuable guide to tracking the progression of stroke.”
For brain tumors, neurosurgeons often use MRI to map the patient’s brain so they can avoid cutting into vital structures, but soon they may use DTI as well to locate axons that must not be cut during surgery.
DTI also provides insights into psychiatric problems such as schizophrenia, which may be caused by faulty neural transmissions rather than conspicuous structural abnormalities. For example, Kelvin O. Lim, a psychiatry professor at the University of Minnesota Medical School, has traced the memory and cognitive problems of schizophrenia to axons near the hippocampus, a brain structure crucial for the creation of short-term memories.