VIEW OF THE BRAIN THROUGH A FLOW-COLORED TIME WINDOW

Radioactive tracer substances administered to study cerebral functions open a time-dependent window to the brain. We can study e.g. regional cerebral blood flow (rCBF) or chemical properties such as receptors f or transmitter substances. Since the tracer substance is carried by th e blood flow into the brain its initial distribution will be proportio nal to the rCBF. The possibility to study more specific brain function s depends on the available time for redistribution of the tracer subst ance according to its specific chemical affinity. I have studied with the aid of a simple mathematic model the time needed for distribution and redistribution of freely diffusable tracer substances in the brain . The results indicate that SPECT measurements of brain receptor prope rties in theory give at least as good recording conditions as correspo nding PET studies. Clinical SPECT receptor studies will presumably soo n contribute to our knowledge of the epileptic pathogenic mechanisms.