Cerebral blood flow determination by rapid-sequence computed tomography: theoretical analysis.

Dynamic computed tomography (CT) using rapid-sequence scanning can be used to determine cerebral blood flow noninvasively following an intravenous bolus injection of contrast material. Since the contrast material remains intravascular in the normal brain, principles of indicator dilution analysis for nondiffusible indicators are applied to the time course of the changes in contrast concentration. While a delay is introduced by the relatively prolonged intravenous injection, this can be corrected for if the arteries are seen on the scan; the corrected mean transit time of the first passage of the bolus through the vessels gives the blood flow per unit vascular volume. To find the blood flow per unit of total tissue volume requires measuring the concentration of contrast material in the blood, which cannot always be done directly from brain scans with current CT equipment; however, a relative volume for total tissue flow can be found by using the area under the curve of contrast concentration as a function of time, as this area is proportional to the fractional vascular volume of the tissue.