Update on diffusion tensor imaging in Alzheimer's disease.

With estimates of more than 5 million people with Alzheimer's disease (AD) now living in the United States and an increasing prevalence of the disease among the aging population, there is an urgent need for the development of reliable biomarkers for early diagnosis and evaluation of potential therapeutic interventions. Structural MR imaging, the focus of the most intense research in this area to date, has identified characteristic patterns of macroscopic atrophy within larger groups of patients who have clinically probable AD, particularly within the medial temporal lobes. These changes are thought to reflect underlying neuronal cell death, and as a result are consistently demonstrated only in the late stages of the disease. Paralleling the development of new molecular markers for AD pathology in nuclear medicine are a number of encouraging results in the application of functional, perfusion, and diffusion imaging which point to a growing role for MR imaging in the evaluation of AD. This article surveys current research on the use of diffusion MR imaging for the evaluation of patients who have mild cognitive impairment and AD, and summarizes the important unifying results that are beginning to emerge on the potential role for diffusion imaging in practice.