Positron imaging of cerebral blood flow during continuous inhalation of C15O2.

Abstract

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....

Early venous drainage after successful endovascular recanalization in ischemic stroke — a predictor for final infarct volume?

“…The outcome of such areas was universally poor, exhibiting necrosis on late structural imaging [17][18][19][20][21][22][23]. Postischemic hyperperfusion has also been documented in various animal studies [18][19][20][21][22][23]. Yonas et al [24] showed that 20 min of vascular occlusion in baboons resulted in a brief episode of hyperperfusion with no subsequent alteration seen on CT and only minimal random neuronal injury.…”

Noninvasive Tomographic Study of Cerebral Blood Flow and Oxygen Metabolism in vivo

“…OEF and CM R02 using the ECAT system were relatively unsatisfactory [6] and conflicted with results obtained by others using a differ ent PET system [3]. This raised questions concerning the validity of the 'sO continuous inhalation model, for which only indirect evi dence was available [2], However, a better understanding of the above-mentioned tech nological difficulties led to designing an ex perimental study in baboons, using the wellknown relationship between CBF and PaCOj, that clearly demonstrated that C150 2 continuous inhalation allows tomographic measurement of CBF [9], During the course of this study, a point was raised concerning the consequences of the nonlinearity of the tissue H2i50-CBF relationship. In this regard, the inescapable admixture of two compo nents with different blood flows and water partition coefficients -namely, gray and white matter whatever the size and loca tion of the region under consideration, results in systematic underestimation of the com puted CBF by as much as 25%.…”

Pharmacokinetics of a triarylmethyl‐type paramagnetic spin probe used in EPR oximetry

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