Dr. Bradley is Director of MRI at Long Beach Memorial Medical Center in Long Beach, CA, and Professor of Radiology at the University of California, Irvine, in Orange, CA. Dr. Dietrich is Professor of Radiological Sciences and Director of MRI at the University of California, Irvine, in Orange, CA. She is also a member of the editorial advisory board of this journal.

A s we enter the new millennium, it is apparent that one major disease has benefited little by our improved ability to image it: acute stroke. Recently, however, the increased availability of EPI diffusion/perfusion imaging has given us a new and improved look at the physiology underlying the extension of infarction following an initial vascular occlusion. We are now able to distinguish reversible cytotoxic edema from irreversible infarction, and to identify the "ischemic penumbra" (i.e., the area of brain at risk for extension of the initial infarction).

A recent phase III clinical trial of a new neuroprotective agent used the volume of the lesion, as seen on EPI diffusion imaging, as an entry condition. Efficacy was defined by the difference between the volume of the abnormality on the initial diffusion image and the volume of the abnormality on the final T2-weighted image. This finding was significant because, for the first time, objective MR measurements were used instead of subjective stroke rating scales.

Undoubtedly, our success in improving the ability to visualize subtle physiologic changes resulting from infarction will lead to the introduction of new neuroprotective agents. We will soon be able to actually save brain tissue, rather than the alternative of merely teaching the stroke patient how to function as best he can with the remaining brain tissue. Neuroprotective agents also will play a similar role in salvaging the brain of infants who have suffered anoxic-ischemic insults.

We look forward to the role MRI will play in the introduction and implementation of these new neuroprotective agents. The potential ability to save brain tissue represents the most significant effect MRI has had on patient outcome since its introduction almost two decades ago.