Modeling approach to eliminate the need to separate arterial plasma in oxygen-15 inhalation positron emission...

A mathematical model has been developed to predict the arterial metabolite concentration curve using the whole blood radioactivity curve in positron emission tomography (PET) during 15O2 inhalation. Production of arterial H2 15O due to aerobic metabolism in the body was modeled as a single rate constant, which was determined from 200 steady-state values of plasma and whole blood concentrations recorded during continuous inhalation of 15O2 and C15O2. Comparison of this method in eight 15O2 inhalation studies (four at rest and four during motor stimulation) performed on four subjects resulted in: (1) arterial H2 15O curves that were well matched in shape to those measured by the frequent plasma separation and (2) cerebral metabolic rate of oxygen (CMRO2) and cerebral blood flow (CBF) were consistent with those obtained by the frequent plasma separation procedure (maximum difference was 3%). An error sensitivity analysis was also performed and demonstrated that errors expected in this modeling approach caused only negligible errors in CMRO2 and CBF estimates. Thus, the arterial H2 15O concentration curve can be accurately predicted using the whole blood time-activity curve; hence, plasma separation can be avoided in 15O2 inhalation PET.