Diffusion tensor imaging at 1.5T MRI just was not practical. While MRI at 1.5T could generate diffusion tensor maps, it required lengthy scan times to get resolution decent enough to eliminate noise and reveal fiber bundle tracking. The increased signal-to-noise ratio at 3T makes it possible to produce fiber tracking maps in two to three minutes. As a result, DTI at 3T is becoming a standard part of imaging patients with neurological disease.

The technique capitalizes on the anisotropic movement of water in brain white matter. While water diffuses randomly in gray matter, it moves in only one direction in white matter: parallel to the orientation of the fibers. By determining the degree of anisotropy and by tracking the path of white matter fibers, DTI and tractography help radiologists examine the overall architecture of white matter and assess the integrity of the fibers in a variety of brain pathologies, including multiple sclerosis, AIDS, and Alzheimer's disease, as well as in psychiatric disorders and trauma.

DTI can evaluate any structure whose internal fibers are anisotropic, including muscle. DTI assesses neurological conditions in several ways. The diffusion tensor, which mathematically models diffusion in 3D, elicits measurements of relative and fractional anisotropy (FA) in MS and AIDS, and anisotropy imaging looks at alterations in the aging brain.

In recent clinical investigations, reductions in anisotropy have been seen in areas of brain and spinal cord that have been subjected to traumatic injury and in psychiatric conditions such as schizophrenia and depression. A pair of studies reported at the 2007 annual meeting of the RSNA relate findings on DTI with the site and degree of impairment following traumatic neurological injury.

In one study, from the University of Maryland Medical Center, DTI parameters were significantly decreased at all sites of spinal cord injury, and the most pronounced reductions occurred in patients who had hemorrhagic cord contusion. DTI differed even in patients who exhibited no signs of contusion on conventional MR scans. The research compared imaging results from 50 patients who had neck trauma and 11 normal volunteers.

In the other study, from the Walter Reed Army Institute of Research, in Bethesda, MD, DTI detected cerebral compromise following mild traumatic brain injury that remained hidden on standard anatomical MRI. The study evaluated imaging examinations performed on 11 soldiers who had sustained mild traumatic brain injury while serving in Iraq. At three-month follow-up, FA was lower than baseline values in four soldiers who also had signs of deteriorating attention span, executive function, and memory on standardized neuropsychological tests. However, FA was higher in seven soldiers whose neuropsychological function improved.

A preliminary study from the People's Republic of China suggests that DTI may identify an abnormality in the microstructure of white matter in patients who fail to respond to drug treatment for depression. FA was significantly lower in frontal white matter in nine patients with major depression who did not respond following eight weeks of therapy with a selective serotonin-reuptake inhibitor.