Cerebral Blood Flow Measurements Using Stable Xenon CT with Very Short Inhalation Times

A noninvasive, simplified method using inhalation of stable xenon (Xe^s ) and computed tomographic (CT) scanning to estimate regional cerebral blood flow (rCBF) and regional partition coefficient (rλ) is described. Twenty-four patients with cerebrovascular occlusive disease and six volunteer controls inhaled 30 % Xe^s and 70 % oxygen for 180 seconds and exhaled for 144 seconds during serial CT scanning without denitrogenation. The end-tidal Xe^s concentration was continuously monitored with a thermoconductivity analyzer to determine the build-up range (A value) and build-up rate constant (K value) for arteries with the curve fitting method. The time-CT number (Hounsfield unit) curve for cerebral tissue during the Xe^s washin and washout phases was used to calculate rλ and rCBF using least squares curve fitting analysis. The resultant rλ and rCBF map demonstrated a reliable distribution between the gray and white matter, and infarcted areas. rCBF was high in gray matter, low in white matter, and much lower in infarcted areas than in white matter. rλ was high in white matter, low in gray matter, and much lower in infarcted areas. Xe^s CT-CBF studies with very short inhalation of 180 seconds is a clinically useful method for evaluation of rCBF in patients with cerebrovascular diseases.