1. Method for examining a living subject by non-invasive imaging, comprising the steps of: (a) administering a contrast agent to a living subject; (b) obtaining a plurality of successive images, each containing a region of interest of said subject, by non-invasive imaging after administering said contrast agent, said contrast agent having a physical property which is identifiable in said images; (c) determining a set of quantitative values of said physical property in each of said images, and generating a histogram, for the region of interest in each of said images of the quantitative values of the physical property in the set for that image, said histogram indicating a frequency of occurrence in the region of interest in of the respective quantitative values in the set; and (d) determining a concentration of said contrast agent in said region of interest dependent on said frequency of occurrence in the region of interest in.