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

摘要

We aimed at evaluating the adequacy of the commonly employed compartmental model for quantitation of cerebral metabolic rate of oxygen (CMRO2) using ¹⁵O-labeled oxygen (¹⁵O2) and positron emission tomography (PET). Sequential PET imaging was carried out on monkeys following slow bolus injection of blood samples containing ¹⁵O2–oxyhemoglobin (¹⁵O2–Hb), ¹⁵O-labeled water (H2¹⁵O), and C¹⁵O-labeled hemoglobin (C¹⁵O–Hb) into the internal carotid artery (ICA). Clearance slopes were assessed in the middle cerebral artery territory of the injected hemisphere. The time–activity curves were bi-exponential for both ¹⁵O2–Hb and H2¹⁵O. Single exponential fitting to the early (5 to 40 seconds) and late (80 to 240 seconds) periods after the peak was performed and the ¹⁵O2–Hb and H2¹⁵O results were compared. It was found that a significant difference between the clearance rates of the ¹⁵O2–Hb and H2¹⁵O injections is unlikely, which supports the mathematical model that is widely used to describe the kinetics of ¹⁵O2–Hb and H2¹⁵O 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.