Positron Imaging of Cerebral Blood Flow During Continuous Inhalation

This investigation tests the hypothesis that the normal cerebral image obtained non-invasively during continuous inhalation of C"O, is related to cerebral blood flow. Trace amounts of CO, labeled with the positron-emitting radionuclide " 0 were administered to 4 normal subjects at normoand hypocapnia and to 2 of these subjects at hypercapnia. Hypocapnia typically caused a marked decrease in cerebral " 0 activity, and hypercapnia a small increase in activity. The relative difference in the change in count rate in response to hypoand hypercapnia is what one would expect if the activity represented blood flow, according to a mathematical model which assumes the " 0 label enters the brain as water of perfusion. The findings in this study suggest that the normal cerebral image obtained during continuous inhalation of C"02 is related to cerebral blood flow, but in a non-linear fashion, and that the technique would be more sensitive to ischemic events than to hyperemic phenomena. Stroke, Vol. 11, No. 1, 1980