Metabolite correction in [15O]O2 studies
In [15O]O2 studies, the labeled water formed during the study is assumed to be evenly distributed between blood cells and plasma, while labeled oxygen stays only in the blood cells. Blood curve (total [15O]) is measured using blood pump and on-line detector, and processed as usual. For metabolite analysis, plasma curve ([15O]H2O) is measured from additional blood samples. The plasma curve is converted to metabolite ([15O]H2O) concentration curve in blood withthe help of haematocrit value, using program o2_p2w. With these curves, the rates of formation and removal of labeled water is calculated using fit_o2bl. Then, the separated TACs of authentic [15O]O2 and metabolite [15O]H2O in blood can be calculated using program o2metab.
To measure oxygen consumption in the brain, it is usually not necessary to correct the input curve for labeled water. If metabolite correction is required, individual measurements may sometimes be replaced by rate constants determined for a similar group.
