Current Clinical Applications of Diffusion-Tensor Imaging in Neurological Disorders

Abstract

Diffusion-tensor imaging (DTI) is a noninvasive medical imaging tool used to investigate the structure of white matter. The signal contrast in DTI is generated by differences in the Brownian motion of the water molecules in brain tissue. Postprocessed DTI scalars can be used to evaluate changes in the brain tissue caused by disease, disease progression, and treatment responses, which has led to an enormous amount of interest in DTI in clinical research. This review article provides insights into DTI scalars and the biological background of DTI as a relatively new neuroimaging modality. Further, it summarizes the clinical role of DTI in various disease processes such as amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease, Alzheimer's dementia, epilepsy, ischemic stroke, stroke with motor or language impairment, traumatic brain injury, spinal cord injury, and depression. Valuable DTI postprocessing tools for clinical research are also introduced.

Keywords: diffusion-tensor imaging; diffusion-tensor imaging scalar; neurological disorders; postprocessing.

Fig. 1. DTI scalar images derived from diffusion-tensor images with 20 gradient directions. The FA is a DTI scalar that represents axonal integrity and is strongly related to fiber integrity. The AD is related to axonal damage. The RD is probably a DTI marker of myelin, with an increased RD value suggestive of myelin damage in white matter tissue. The MD is a measure of the average molecular motion. The size and integrity of cells affects the MD, which is known to be related to necrosis, edema, and cellularity. The MO is a probabilistic tractography measure for crossing white matter fibers. AD: axial diffusivity, DTI: diffusion-tensor imaging, FA: fractional anisotropy, MD: mean diffusivity, MO: mode, RD: radial diffusivity.

Fig. 2. Frontal-habenula-cerebellar and frontal-cerebellar tracts. The long fiber pathway connecting the frontal cortex via the habenula to the cerebellum (left) and the frontal-cerebellar tracts (right) were tracked using 3-T, 64-direction diffusion-tensor imaging data, analyzed using DSI Studio software.

Fig. 3. Diffusion-tensor tractography in a patient (a female aged 74 years) with left hemiparesis after suffering an infarction in the right corona radiata (arrow in lower left figure) and basal ganglia (arrow in upper right figure). The right CST exhibited marked decreases in the number of fibers [n=234 on the right (blue) and n=876 on the left (red)] and in fractional anisotropy (0.4267 and 0.5483, respectively), but the continuity of the right CST was preserved throughout its course. CST: corticospinal tract, L: left, R: right.

Fig. 4. Three levels of damage to the left AF. DTI of the AF (left column) and T2-weighted magnetic resonance images (right column) show three types of AF (blue, right AF; red, left AF) categorized according to the severity of damage. In type A, fibers of the AF are severely damaged and thus are not visualized in DTI reconstructions. In type B, the AF is disrupted between Wernicke's and Broca's areas. In type C, the AF is preserved around the brain lesion. The arrow indicates disruption of the left AF around the stroke lesion. AF: arcuate fasciculus, DTI: diffusion-tensor imaging.