Cerebral blood flow imaging by spect using Xenon-133

Three different approaches are currently being taken for obtaining tomographic images of cerebral blood flow, CBF, in man. The positron emittors involve the use of a very costly technology. This practically excludes its wider application. The non-radioactive (''cold'') Xenon inhalation approach based on a slight enhancement in X-ray absorption on CT-scanning cannot be considered to be reliable. Moreover Xenon in the concentration used increases CBF (Junck et al. 1985) and has slight anesthetic properties. The present paper concerns the third type of tomographic CBF imaging, namely the one based on single photon emission computerized tomography, SPECT. Special attention is given to the Xenon-133 inhalation method as the chemical inertness of this tracer secures, that only simple physical processes as convection (flow), diffusion and solubility influences its distribution. Xenon-133 is a practical isotope, it is relatively cheap and has a long half-life. But, because of its low energy it is not ideal for tomography, as Compton scatter in the brain reduces contrast in the image. Comments will also be made on the use of other single photon emitting radionuclides for CBF tomography by SPECT such as Xenon-127, Iodine-123 and Technetium-99m