Perfusion CT: Is it Clinically Useful?

Abstract

Combining perfusion CT (CTP) with CT angiography (CTA) and noncontrast CT (NCCT) provides much more information about acute stroke pathophysiology than NCCT alone. This multimodal CT approach adds only a few minutes to the standard NCCT and is more accessible and rapidly available in most centres than MRI. CTP can distinguish between infarct core and penumbra, which is not possible with NCCT alone. A small infarct core and large penumbra, plus the presence of vessel occlusion on CTA may be an ideal imaging ‘target’ for thrombolysis. To date, multimodal CT has predominantly been assessed in hemispheric stroke due to its limited spatial coverage. This will become less of an issue as slice coverage continues to improve with new generation CT scanners. Apart from the concepts above, more specific CTP and CTA criteria that increase (or decrease) probability of response to thrombolytic treatment are yet to be determined. Nonetheless, CTP thus has the potential to improve patient selection for thrombolysis. Introduction Noncontrast CT (NCCT) remains the most widely used imaging modality for acute ( 1 – 3 ). There is now little doubt that MRI is a superior imaging modality to NCCT for diagnosis of acute stroke, being substantially more sensitive without compromising specificity ( 4 ). However, most stroke patients around the world do not have immediate access to MRI ( 1 ). In contrast, multislice CT scanners are now widely available. Multislice CT scanners allow assessment of vessel status with CT angiography (CTA), as well as cerebral perfusion CT perfusion (CTP). These sequences can be performed immediately following NCCT scanning and add only a few minutes to the examination ( 5 ). There is emerging evidence that such ‘multimodal’ CT imaging provides somewhat similar information to MRI about acute stroke pathophysiology, and is clearly more sensitive than NCCT at identifying early ischaemic change in the hyperacute stages of stroke ( 6 – 8 ). Furthermore, multimodal CT may, as has been suggested for MRI, be able to refine patient selection for thrombolysis ( 6 , 9 – 11 ).