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The result of the PSAMPLE correction and calibration procedure is a time vector of total radioactivity concentration in whole blood, which forms the basis for the arterial input function (AIF) in kinetic modeling. In principle, the AIF is derived in two steps from the whole blood activity concentration:

1.The activity concentration in the plasma fraction of whole blood is determined by accounting for concentration differences in whole blood and the plasma, which actually exchanges with tissue.

2.The concentration of unchanged tracer in the plasma (authentic parent) is determined by correcting plasma activity for radiolabeled metabolites.

These corrections require knowledge of the plasma/whole-blood and the parent/metabolite concentration ratios during the experiment, which can be acquired by taking blood aliquots for analysis (i.e. centrifugation to separate plasma, high-performance liquid chromatography or cartridge metabolite separation methods), or by applying standard ratios acquired in a population.

All the related processing steps are implemented in the PKIN tool. Please refer to the PMOD Kinetic Modeling Tool Users Guide for detailed information about the background of the techniques and the implementation in PKIN.