1. Method for estimating a quantity of interest among a plurality of an artery/tissue/vein dynamical system in an elementary volume—referred to as a voxel—of an organ, the 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 the Bayesian method—a posterior marginal probability distribution for said quantity of interest by: assigning a direct probability distribution for the experimental perfusion data given the parameters involved in the problem relating to 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 a soft information related to the impulse response of said dynamical system.