1. A method for simultaneously extracting the input function and pharmacokinetic parameters of an active ingredient in a structure of a living organism from a measurement image of the kinetics of the active ingredient in the structure obtained by an imaging device, the image comprising a plurality of regions of interest inside each of which the kinetics of the active ingredient are measured, comprising the following steps: determining a plurality of sets of kinetics from the measured kinetics, the determined sets of kinetics being different from each other and each determined set of kinetics including several measured kinetics; defining at least one kinetic model, parameters of the defined kinetics model being formed by parameters of an input function and pharmacokinetic parameters; estimating, for each determined set of kinetics, the input function and the pharmacokinetic parameters by resolving the kinetic model defined from the determined set of kinetics; and deducing a final input function and final pharmacokinetic parameters from estimated input functions and estimated pharmacokinetic parameters.