The purpose of this tutorial is to acquaint the radiologist with the pathophysiologic cascade of hemodynamic and metabolic events that occur during stroke and to correlate them with MRI signal in different sequences. An additional objective is to connect this knowledge with neuroimaging including MR spectroscopy, Perfusion MRI and Diffusion MRI to be able to delineate the two main tissue subtypes that characterize ischemic stroke, namely:

• The already irreversibly damaged tissue (‘core’).
• The at-risk tissue (‘penumbra’), which represents the main target for therapy.

Introduction

Cerebrovascular disease is the third leading cause of death (after heart disease and cancer) in the United States; it is also the most prevalent neurologic disorder in terms of both morbidity and mortality. The term cerebrovascular disease denotes any abnormality of brain caused by a pathologic process of blood vessels. “Stroke" is the clinical designation that applies to these conditions, particularly when symptoms begin acutely.

The treatment of acute ischemic stroke remains a major challenge. Although early intra-arterial thrombolysis does benefit many patients, it can have serious harmful effects. Additionally, thrombolysis can be used in only a few percent of cases due to the restricted time-window and limited selection criteria.

Currently, criteria for thrombolytic therapy patient selection are not entirely satisfactory. Specifically, the differentiation of patients who harbor viable ischemically challenged neural tissue from those with completed infarcts who will not benefit from additional therapy remains an enigma.