Local Cerebral Blood Flow and Tissue Solubility Measured by Stable, Xenon-Enhanced Computerized Tomography

The purpose of this chapter is to review pre-liminary experience with the use of the EMI 1010 computerized tomographic (CT) scanner for measuring localized cerebral blood flow and tissue solubility during inhalation of stable xe-non (Xe') gas, which then acts as a freely dif-fusible tracer. Stable xenon is an excellent CT contrast agent comparable to iodine in its ca-pacity for absorbing X-rays (1-7,11-15). After inhalation, Xe ` diffuses rapidly from the lungs into the arterial blood and brain tissue. The gas acts as a tracer by inducing regional changes in CT density as it diffuses through tissues, which are then measured as changes in Hounsfield units (AH) (Fig. 1). Resulting changes in re-gional AH units have been used for measure-ments of local cerebral blood flow (LCBF) and tissue solubility with high resolution in animals (2-7,12). Preliminary research studies can now. be reported in human subjects (11-15). Stable xenon is lipid soluble, hence it is more soluble in white matter than in gray matter. Fur-thermore, local tissue solubility may be esti-mated when the level of Xe ' approaches tissue saturation. In pathological states, such as brai