TRANSFORM METHODS FOR TRACER DATA ANALYSIS

The analysis of experimental data from radioactive tracer studies presents many difficulties. I n such systems the tracer material may be simultaneously undergoing several physiological processes ; for example, diffusion, chemical interaction, and so on, at different rates in numerous biological compartments of varying sizes. To minimize these complexities, a biological system is often considered in terms of a simplified compartmental model. The modal is represented by a series of compartments within which the isotope may mix. Flow or diffusion may exist within compartments or activity may be lost from a compartment as in the process of secretion. The validity of such models is limited to the extent that the behavior of the idealized system actually produces data which duplicate those obtained in a real system. It is further assumed in such studies that the system is in steady state; that is, the relative amount of stable material in each compartment remains unchanged during the course of the experiment. Such an assumption carries the implication that the inflow and outflow of stable material must be equal. It has been shown previously in studies by Sheppard and Householder (1951) and by Berman and Schoenfeld (1956) that the behavior of labeled substances in such steady-state compartmental systems can be represented by linear differential equations and that the solution consists of a sum of exponentials: