ABSTRACT
The methods for deriving tumor perfusion data from dynamic contrastenhanced computed tomography (CT) images outlined in the previous chapters can be applied to regions of interest (ROI) constructed on the basis of anatomical features visible on conventional CT images. However, abnormalities of tumor 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 CT slice 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 or even magnetic resonance imaging. Indeed, in addition to images of tumor blood flow, a whole range of parametric maps can be produced in this way (Table 4.1). Figure 4.1 shows the appearance time (Figure 4.1a), blood flow (Figure 4.1b), blood volume (Figure 4.1c), and capillary permeability surface area product (Figure 4.1d) of a brain tumor in the right cerebral hemisphere. The tumor (arrow in Figure 4.1d) is clearly delineated in the blood flow (F), blood volume (Vb), and capillary permeability surface area product (PS) parametric maps as having a hypervascular rim surrounding a hypovascular core, with high blood flow, blood volume, and capillary permeability surface area product in the rim but low values in the core. There are also two distant metastases (arrowheads in Figure 4.1d) which are visible as focal regions of increased PS and blood flow. In the normal brain, there is clear differentiation between gray and white matter in both blood flow and blood volume. In the appearance time map, the distinction between gray and white matter is less, suggesting
that the arrival times for gray and white matter are more similar than their blood flows and volumes.
