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To determine whether renal blood flow can be measured by positron-emission tomography (PET) during constant infusion of rubidium-82 (82Rb) using a steady-state kinetic model, studies were performed in 10 dogs at control (n = 10), during mild flow reduction (n = 7), during severe flow reduction (n = 10), and after reperfusion of the kidney (n = 3). PET data were quantified to determine mean concentration of 82Rb (Ct) in each transverse section of the kidney. The arterial concentration (Ca) of 82Rb was measured by well counting of arterial blood samples during the equilibrium scan. 82Rb renal uptake (Ct/Ca) correlated nonlinearly with microsphere renal blood flow according to a steady-state kinetic model (r = 0.90). 82Rb estimated flow was 3.16 +/- 1.36 ml X min-1 X g-1 at control and 1.56 +/- 0.57 and 0.37 +/- 0.59 during mild and severe flow reductions, respectively. Microsphere determined flow was 2.89 +/- 0.77 ml X min-1 X g-1 at control, 1.58 +/- 0.42 at mild reduction, and 0.27 +/- 0.49 at severe reduction. In the occlusion and reperfusion model, the 82Rb estimated flow during occlusion was 0.21 +/- 0.15 ml X min-1 X g-1 and on reperfusion went up to 2.13 +/- 1.08. The contralateral kidney demonstrated reductions in the 82Rb estimated flow of 3.02 +/- 1.62 ml X min-1 X g-1 (63%) and 2.92 +/- 0.89 (61%) during mild and severe flow reductions, respectively. We conclude that PET with 82Rb permits serial quantitative assessment of renal flood flow.

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SUMMARY 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 normo-and 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"0 2 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 2 have suggested that because the l 5 0 label transfers to water in its passage through the lungs 3 it enters the brain as water of perfusion and distributes there in proportion to CBF. During continuous inhalation the short half-life of the label (T x h = 124 sec) facilitates rapid establishment of a dynamic equilibrium, at which time the amount of label entering the brain equals that leaving through physiologic wash-out and radioactive decay. Brain images obtained at equilibrium should provide qualitative measures of CBF, flow being proportional to the count rate and to the corresponding brightness of the cerebral image.The C 16 O 2 technique is attractive because it is noninvasive, potentially quantifiable, 4 and when paired with studies made during continuous inhalation of 15 O 2 theoretically can provide oxygen metabolism information.5 Before beginning patient trials with this technique, however, we wished to determine if changes in CBF in physiologic ranges could produce detectable changes in cerebral count rates and whether the identifiable alteration in activity might be appropriate for a flow index. We therefore applied the method in normal volunteers at rest and during marked changes in Paco 2 .This report discusses the effects of large alterations in Paco 2 on the brain images obtained in 4 normal subjects during continuous inhalation of trace No previous studies had been undertaken to show that changes in CBF within physiologic ranges might be identified with this technique. The results of this study served as the rationale for our subsequent patient investigations. Methods 15O is a cyclotron-produced positron-emitting radionuclide with a 2 minute half-life. Its distribution in brain can be imaged by detecting the photons released following positron emission. Positrons are positive electrons emitted in the decay of certain nuclei. Interaction of the positron with an electron leads to an annihilation process in which the masses of these particles are converted to two 511 KeV photons travelling in opposite directions....

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