ABSTRACT

The methods for deriving perfusion data from dynamic contrast-enhanced CT images outlined in the previous two chapters can be applied to regions of interest (ROI) constructed on the basis of anatomical features visible on the conventional CT images. However, abnormalities of perfusion may not be readily apparent on conventional CT images and therefore the ability to place ROIs over areas of physiological importance is severely limited. If perfusion values are calculated using time-attenuation data derived from individual pixels, it is possible to generate a parametric map depicting blood flow throughout the whole slice of brain chosen for the dynamic study. The spatial resolution of these CT perfusion images is identical to that of conventional CT and thus superior to other techniques such as positron emission tomography (PET) and magnetic resonance imaging. Indeed, in addition to images of cerebral blood flow (CBF), a whole range of parametric maps can be produced in this way (Table 5.1). Figure 5.1 shows the To, CBF, cerebral blood volume (CBV), mean transit time (MTT) and perfusion-weighted maps of a patient with stroke in the right middle cerebral artery territory.