Characterization of a gas-purge method to access 11C-carbondioxide radioactivity in blood

Carbon-11 labeled radiotracers, such as 11C-acetate and 11C-palmitate are widely used in positron emission tomography (PET) for noninvasive evaluation of myocardial metabolism under varied physiological conditions.These tracers are attractive probes of tissue physiology, because they are simply radiolabled versions of the native biochemical substrates. One of the major metabolites generated by these tracers upon the administration is 11CO2 produced via the citric acid cycle. In quantitative modeling of 11C-acetate and 11C-palmitate PET data, the fraction of blood 11C radioactivity present as 11CO2 needs to be measured to obtain a correct radiotracer arterial input function. Accordingly, the literature describes a method whereby the total blood 11C-activity is counted in blood samples treated with base solution, while the fraction of 1 1CO2 is measured after the blood is treated with acid followed by a 10 minutes gas-purge. However, a detailed description of the experimental validation of this method was not provided. The goal of this study was to test the reliability of a 10 minute gas purging method used to assay 11CO2 radioactivity in bloo