Cerebral Blood Flow Tomography Using Xenon 133 Inhalation — Methodological Considerations

Abstract

Three tomographic techniques for measurement of cerebral blood flow (CBF) are currently being explored for clinical use. They are all founded upon the use of digital computers for image reconstruction based on a series of lateral projections. In 1978 Drayer et al. described the use of stable xenon combined with conventional CT scanning, viz. single-photon transmission tomography. Because the enhancement is small, the signal-to-noise ratio is very unfavorable. The high cost of stable xenon and the difficulty in obtaining a sequence of CT scans at several levels simultaneously also limit the clinical usefulness of the method (Gur et al. 1981). Positron emission tomography (PET) based on coincidence counting of the annihilation photons has been developed over the last decade. In 1979 Yamamoto et al. described the use of krypton 77 for obtaining CBF tomograms using the inert gas clearance principle. Other positron emitting tracers, notably oxygen 15 labeled C0₂ or H₂0, have also been used (see, e.g., the reports from the 10th and 11th International Symposia on CBF and Metabolism, 1981 and 1983). The clinical usefulness of these techniques is, however, limited by their cost and cumbersomeness, and they have so far been reserved for use in clinical research.