Diffusion tensor imaging and its application to neuropsychiatric disorders

Abstract

Magnetic resonance diffusion tensor imaging (DTI) is a new technique that can be used to visualize and measure the diffusion of water in brain tissue; it is particularly useful for evaluating white matter abnormalities. In this paper, we review research studies that have applied DTI for the purpose of understanding neuropsychiatric disorders. We begin with a discussion of the principles involved in DTI, followed by a historical overview of magnetic resonance diffusion-weighted imaging and DTI and a brief description of several different methods of image acquisition and quantitative analysis. We then review the application of this technique to clinical populations. We include all studies published in English from January 1996 through March 2002 on this topic, located by searching PubMed and Medline on the key words "diffusion tensor imaging" and "MRI." Finally, we consider potential future uses of DTI, including fiber tracking and surgical planning and follow-up.

FIGURE 1

Difference between unrestricted (isotropic) and restricted (anisotropic) diffusion within the brain. The shape of the tensor ellipsoid is determined by the strength of the diffusion along three principal directions (its eigenvectors). In nonrestrictive media such as cerebrospinal fluid, where diffusion is equal in all directions, the tensor can be visualized as a sphere. In restrictive media such as white matter, where diffusion is different in all directions, the tensor can be visualized as an ellipsoid.

FIGURE 2

Visualization of diffusion tensors. The blue lines represent the in-plane component of the principal diffusion direction; the other colors show the magnitude of the out-of-plane component, with orange/red indicating maximal diffusion. The white and green arrows point to the corpus callosum and the anterior commissure, respectively, two major fiber tracts with the largest in-plane diffusion component, while the blue and pink arrows indicate the cingulate and uncinate fasciculi, fibers with the biggest out-of-plane diffusion component.

FIGURE 3

Three-dimensional tractography of a normal subject, showing the anterior (white) and posterior (blue) portions of the corpus callosum as well as the left and right (yellow and green) corticospinal tracts. These tracts pass through an axial section of the lateral ventricles.