Stroke is a leading cause of death in Western countries, with a mortality rate higher than most forms of cancer and now the commonest cause of long-term adult disability. Stroke diagnosis and management were revolutionized by the widespread introduction of computed tomographic (CT) scanning in the 1970s. CT scanning sensitively excludes cerebral hemorrhage, but early ischemic changes can be subtle. In the first few hours after stroke onset, when acute therapies such as thrombolysis are being considered, CT is often normal, although acute ischemic changes have become better recognized in recent years. Conventional magnetic resonance imaging (MRI) became widely available in most countries a decade after the advent of CT scanning, but has had a limited role in stroke diagnosis and management. Although MRI provides far better imaging of posterior fossa structures and facilitated non-invasive angiography (MRA), its sensitivity in acute stroke is not much better than CT. Other functional imaging techniques such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) have been valuable research tools, but have not been of routine clinical use in the management of stroke.

Since the 1990s, the increasingly widespread availability of echoplanar MRI technology facilitated the introduction of diffusion-weighted imaging (DWI), perfusion imaging (PWI) and magnetic resonance spectroscopy (MRS). Diffusion-weighted imaging allows the hyperacute evaluation of the ischemic core within minutes of stroke onset and the distinction between acute and chronic ischemic lesions.