Magnetic resonance imaging in acute stroke

In this issue of Neurology are two articles describing further experience with magnetic resonance diffusion weighted imaging (DWI) and perfusion weighted imaging (PWI) in acute ischemic stroke.1,2 Both add to the growing body of evidence from clinical observation and animal experiments documenting that these new MRI techniques show abnormalities in regions of acute cerebral ischemia earlier than either conventional MRI or CT. We would like to discuss the use of MRI as a diagnostic test for acute ischemic stroke in the context of the practice of clinical neurology. We will not discuss the use of MRI for clinical research or treatment trials because the requirements for a diagnostic test under these circumstances are quite different. In the practice of medicine, the usual purpose of a diagnostic test is to improve the accuracy of the initial clinical diagnosis. The goal of improved diagnostic accuracy is not an end in itself, but a means to improve patient outcome by allowing selection of the most appropriate therapy. Thus, the value of a diagnostic test is determined not only by its accuracy but by demonstrating that the information it provides can be used for selecting the most effective patient management. Even in circumstances where no proven treatment exists, more accurate diagnosis can prevent the use of inappropriate treatment and provide prognostic information which is of value to patients and their families. A new diagnostic test is useful if it can replace a more invasive or expensive test or if it provides information that can be shown to improve …