The role of neuroimaging in acute stroke.

Background: There is a need for early recognition, diagnosis, and therapy in patients with acute stroke. The most important therapies are thrombolysis or aspirin in hyperacute ischemic stroke and, for secondary prevention, antiplatelet agents, statins, ACE inhibitors (for lowering blood pressure), warfarin, and carotid endarterectomy or stenting. Imaging technology has a crucial role to play in the diagnosis and treatment of stroke. In recent years, significant advances have been made due to the availability of physiological imaging using a variety of techniques, ranging from computerized tomography (CT) to magnetic resonance imaging (MRI), which enable clinicians to define brain anatomy and physiology in greater detail than ever before.

Objective: In this article we discuss the imaging techniques currently available for patients with acute stroke, with an emphasis on the utility of these techniques for diagnosis and refining patient selection for early interventions. This is placed in the context of the needs of developing countries.

Discussion: Although noncontrast CT (NCCT) remains the most commonly used imaging modality to differentiate between ischemic and hemorrhagic stroke, to identify early CT changes, and to rule out stroke mimics, it is not sensitive enough to identify the infarct core or the mechanism of ischemic stroke. MRI, including magnetic resonance angiography (MRA), is the most useful imaging modality for the evaluation of acute stroke; it provides information about the mechanism as well as the vascular territory of the stroke. MRI also provides complete information about the status of tissue through diffusion-weighted imaging (DWI) and about arterial patency by means of MRA. DWI shows acute lesions within minutes of onset of ischemia, while MRA can evaluate extracranial as well as intracranial vessels Evaluation of the proportion of penumbra infarcted tissue is another issue to be considered when instituting thrombolysis, and its clinical usefulness is being assessed in a number of ongoing trials. Penumbral tissue can be identified by perfusion MRI. CT perfusion (CTP) is an emerging alternative, providing similar information about the penumbra and infarct core. A combined approach of NCCT, CT angiography (CTA), and CTP is now being employed at many centers and is known as multimodal CT imaging (MMCT). MMCT provides information about the pathophysiology of acute stroke which is comparable to that provided by MRI, and the technique has the potential to refine patient selection for thrombolysis.