ABSTRACT
In this chapter the theory of computed tomography (CT) brain perfusion measurement is discussed. Because of the small linear attenuation coefficient difference, flowing blood cannot be differentiated from brain parenchyma. To measure brain perfusion with CT, contrast is injected intravenously to ‘label’ the blood. Assuming that the contrast is uniformly mixed with blood, tracing blood through the cerebral circulation is equivalent to tracking a bolus of contrast through the brain. We thus can make use of the extensive literature on tracer kinetics modeling to address the problem of CT perfusion in the brain. A typical CT perfusion imaging protocol with a multirow detector CT scanner may use the follow settings: 4 (8) × 5 mm collimation, 80 kVp, 200 mA, 1 s rotation and scanning for 40-50 s after a delay of 3-5 s from the start of intravenous injection of contrast.1-3 The volume of contrast injected is typically 40-50 ml; however, the rate of injection is either 4-5 ml/s1,3 or higher2,4 depending on the method of analysis adopted, as discussed below. Images are reconstructed at 0.5-1 s image intervals and contrast enhancement in arteries and parenchymal tissue is analyzed by methods described below to arrive at functional maps of cerebral blood flow, cerebral blood volume and mean transit time.
