Xenon CT CBF mapping derived from two minutes inhalation

The validity of a modified short-duration inhalation method in xenon enhanced CT for measuring regional cerebral blood flow (rCBF) was examined. rCBF was calculated from equations derived from autoradiographic images with a fixed partition coefficient of λ = 1, and was imaged as mapping. One minute and forty-five seconds was the optimal scan point to gain an autoradiographic image in view of a balance between linearity of rCBF/enhancement curve and total amount of tissue enhancement. The theoretical errors due to the assumption for a fixed partition coefficient were calculated to be 8 % underestimation for gray matter and 5 % overestimation for white matter. Xenon clearance was attained in 20 min after a scanning, allowing scanning to be repeated in 20-min intervals. Xenon CT CBF mapping for 20 patients yielded satisfactory reproducibility. The simplified inhalation method may minimize anesthetic effects of xenon, reduce the cost of xenon, and shorten the time required for CT scanning. It may also make it easy to perform rCBF mapping by multiplane tomography and stress test. (Namekawa, K.)