Principle and Applications of Diffusion Tensor Imaging

Abstract

Diffusion tensor imaging (DTI) is an emerging magnetic resonance imaging (MRI) technology. Using this technique, we can characterize the way water diffuses inside imaging objects. For example, water molecules inside a cup can diffuse freely in all directions (“free diffusion” or “isotropic diffusion”). On the other hand, water molecules inside living systems often experience numerous “obstacles”, such as protein fibers, membrane, and organelles. If the water diffusion is restricted by these structures it is called “restricted diffusion.” If water molecules are in an environment with highly ordered (or aligned) structure, they tend to diffuse along the structure, resulting in so-called “anisotropic diffusion.” In other words, the water diffusion has “directionality”. The water diffusion, thus, carries a wealth of information on the micro-architecture of the imaging object. Using the DTI, we can characterize the water diffusion process. DTI can answer questions about diffusion like, “is it free or restricted?” or “is it isotropic or anisotropic?” Using the DTI technique, the water diffusion process can be characterized on a pixel-by-pixel basis. Application of the DTI to the brain has revealed that the water diffusion in the brain white matter is highly anisotropic, which is attributed to the highly ordered axonal tracts. The characterization of the anisotropic diffusion can provide detailed information on the white matter architectures, which cannot be obtained by any other radiological tools. In this chapter, we discuss the theory and history of DTI and introduce the state-of-the-art application studies.