Abstract: A noninvasive method of determining function of a target organ using a pre-calibrated imaging system is described. The method contains the steps of introducing an indicator/tracer bolus into the subject's circulatory system and thereafter monitoring simultaneously the responses recorded from the heart/great vessels, and from the target organ. The absolute activity per unit volume of blood withdrawn at a known time(s) is measured, and the observed data from the heart or great vessels is converted into absolute units. These data serve as B(t), the input function. Precalibration of the detector/measuring system allows the observed dynamic indicator/tracer data recorded from the target organ to be expressed in units of absolute activity. These data serve as A(t). A(t) and B(t) are deconvolved in order to obtain the linear response function (LRF, h(t)) for an image element. A preferred method of deconvolution, the DOP method is introduced. Functional images of the target organ's LRF are created.