Imaging-guided acute ischemic stroke therapy: From "time is brain" to "physiology is brain".

The number of potential patients who are actually treated for acute ischemic stroke is disappointingly low, and effective treatments are making a minor impact on this major public health problem. Imaging is not regularly used to identify the ischemic penumbra, a key concept in stroke physiology, though it is capable of doing so in a clinically relevant manner. Evidence is accumulating that identification of the ischemic penumbra and making treatment decisions on the basis of its presence provide substantial benefit to patient outcomes. Moreover, the same studies suggest that an unexpectedly large proportion of patients are suitable for therapy well past the traditional time windows because of the existence of a substantial ischemic penumbra. Modern MR imaging and CT systems, now widely available, are capable of answering the most relevant physiologic questions in acute ischemic stroke. This capability presents new opportunities and responsibilities to neuroradiologists to make appropriate imaging readily available and to have the imaging data rapidly processed and interpreted. In this article, acute ischemic stroke therapy, including the role of imaging in current medical practice, is reviewed, and an evidence-based alternative to contemporary acute ischemic stroke therapy is suggested.