Diffusion Tensor Imaging

Diffusion tensor imaging (DTI) yields images of nerve fiber tracts; different colors indicate the organization of the nerve fibers. Here, a tract originating at the cerebellum is superimposed on a structural-MRI image of a cross section of the brain.

Conventional imaging techniques, such as structural MRI, reveal major anatomical features of the brain -- gray matter, which is made up of nerve cell bodies. But neuroscientists believe that some diseases may be rooted in subtle "wiring" problems involving axons, the long, thin tails of neurons that carry electrical signals and constitute the brain's white matter. With DTI, researchers can, for the first time, look at the complex network of nerve fibers connecting the different brain areas. Lim and his colleagues hope this sharper view of the brain will help better define neurological and psychiatric diseases and yield more-targeted treatments.

In DTI, radiologists use specific radio-frequency and magnetic field-gradient pulses to track the movement of water molecules in the brain. In most brain tissue, water molecules diffuse in all different directions. But they tend to diffuse along the length of axons, whose coating of white, fatty myelin holds them in. Scientists can create pictures of axons by analyzing the direction of water diffusion.

Brain blast: Scientists found that people who suffered concussions as the result of a blast had a more diffuse pattern of brain injury (shown in red) than those whose concussions resulted from a blow to the head or an acceleration injury.
Credit: David Moore et al.

Neuroscientists have begun using DTI to study a host of disorders, including addiction, epilepsy, traumatic brain injury, and various neurodegenerative diseases. For instance, DTI studies have shown that chronic alcoholism degrades the white-matter connections in the brain, which may explain the cognitive problems seen in heavy drinkers. Other DTI projects are examining how the neurological scars left by stroke, multiple sclerosis, and amyotrophic lateral sclerosis (better known as Lou Gehrig's disease) are linked to patients' disabilities.

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