Picturing multiple sclerosis: conventional and diffusion tensor imaging.

Magnetic resonance imaging (MRI) has provided an unparalleled window into understanding multiple sclerosis (MS). Through recognition of relatively specific characteristics of MS, MRI has become an integral part of patient initial evaluation and long-term management. MRI has now been integrated into the formal diagnostic criteria, whereby new lesions can fulfill either dissemination in space or dissemination in time criteria. Long-term MS therapies significantly reduce the development of new lesions as measured by MRI, and clinical trial methodology now routinely uses MRI as the primary outcome in Phase I/II MS trials. Despite the advantages provided by MRI, conventional imaging indicates only the presence of injury to the central nervous system, providing little information on either the severity of injury or its later recovery. Several advanced imaging methodologies such as diffusion tensor imaging (DTI) provide a greater dynamic range for evaluating tissue integrity. DTI has provided useful insights into the pathogenesis of MS, both within lesions as well as within the white matter which appears normal on conventional imaging. Evidence from animal models suggests that DTI may differentiate axonal injury from demyelination and therefore may be useful in the evaluation of neuroprotective therapies.