Adequacy of a compartment model for CMRO2 quantitation using 15O-labeled oxygen and PET: a clearance measurement of 15O-radioactivity following intracarotid bolus injection of 15O-labeled oxyhemoglobin on Macaca fascicularis

We aimed at evaluating the adequacy of the commonly employed compartmental model for quantitation of cerebral metabolic rate of oxygen (CMRO2) using O-15-labeled oxygen (O-15(2)) and positron emission tomography (PET). Sequential PET imaging was carried out on monkeys following slow bolus injection of blood samples containing O-15(2)-oxyhemoglobin (O-15(2)-Hb), O-15-labeled water ((H2O)-O-15), and (CO)-O-15-labeled hemoglobin ((CO)-O-15-Hb) into the internal carotid artery (ICA). Clearance slopes were assessed in the middle cerebral artery territory of the injetted hemisphere. The time-activity curves were bi-exponential for both O-15(2)-Hb and (H2O)-O-15. Single exponential fitting to the early (5 to 40 seconds) and late (80 to 240 seconds) periods after the peak was performed and the O-15(2)-Hb and (H2O)-O-15 results were compared. It was found that a significant difference between the clearance rates of the O-15(2)-Hb and (H2O)-O-15 injections is unlikely, which supports the mathematical model that is widely used to describe the kinetics of O-15(2)-Hb and (H2O)-O-15 in cerebral tissues and is the basis of recent approaches to simultaneously assess CMRO2: and Cerebral blood flow in a single PET session. However, it should be noted that more data are necessary to unequivocally confirm the result.