Local cerebral blood flow by xenon-enhanced CT: current status, potential improvements, and future directions

A noninvasive technique for measuring local cerebral blood flow (CBF) by xenon-enhanced x-ray transmission computed tomography (CT) was developed and reported on extensively in recent years. In this method, nonradioactive xenon gas in inhaled, and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential computed tomography. Time-dependent xenon concentration within various tissue segments in the brain is used to derive both the local partition coefficient (lambda) and CBF in each tissue volume (voxel) of the CT image. A comprehensive assessment of this method reveals that although it provides functional mapping of blood flow with excellent anatomic specificity and has several other significant advantages, there are distinct and important limitations. The assumptions underlying this methodology are examined and the advantages as well as the problems associated with applications of this technique are reviewed. Laboratory and clinical observations that have been made using this technique in recent years are summarized, and potential improvements as well as possible future directions are discussed.