A Physiologic Model for Recirculation Water Correction in CMRO2 Assessment with 15O2 Inhalation PET

Cerebral metabolic rate of oxygen (CMRO2) can be assessed quantitatively using 15O2 and positron emission tomography. Determining the arterial input function is considered critical with regards to the separation of the metabolic product of 15O2 (RW) from a measured whole blood. A mathematical formula based on physiologic model has been proposed to predict RW. This study was intended to verify the adequacy of that model and a simplified procedure applying that model for wide range of species and physiologic conditions. The formula consists of four parameters, including of a production rate of RW (k) corresponding to the total body oxidative metabolism (BMRO2). Experiments were performed on 6 monkeys, 3 pigs, 12 rats, and 231 clinical patients, among which the monkeys were studied at varied physiologic conditions. The formula reproduced the observed RW. Greater k values were observed in smaller animals, whereas other parameters did not differ amongst species. The simulation showed CMRO2 sensitive only to k, but not to others, suggesting that validity of determination of only k from a single blood sample. Also, k was correlated with BMRO2, suggesting that k can be determined from BMRO2. The present model and simplified procedure can be used to assess CMRO2 for a wide range of conditions and species.