When estimating an arterial input function or a patient under study cross calibration factors are generated by comparing nuclear scan data of a radioactive material (e.g. F18) and measuring a sample of the radioactive material in a gamma counter. The derived cross calibration factors are applied to venous samples collected from the patient during a nuclear scan after infusion with a radioactive tracer to convert gamma values counted by the gamma counter into concentration values. The concentration values are used to optimize an initial estimated input function thereby generating an arterialized input function.
