1. A method for estimating a quantity of interest, among a plurality of quantities of interest of an artery/tissue/vein dynamical system, in an elementary volume of an organ, wherein the elementary volume is referred to as a voxel, said method being carried out by a processing unit of a perfusion weighted imaging analysis system, and comprising a step for estimating said quantity of interest from experimental perfusion data, wherein said step comprises evaluating—according to a Bayesian method—a posterior marginal probability distribution for said quantity of interest by: assigning a direct probability distribution for the experimental perfusion data given parameters involved in the estimation of the quantities of interest of the artery/tissue/vein dynamical system in said voxel; and assigning a joint prior probability distribution for said quantities, by introducing purely soft information on an impulse response of said dynamical system and applying the Principle of Maximum Entropy.