1. A system for analyzing a body part of a patient being perfused with a contrast agent capable of circulating within the patient and of being immobilized on a biological target, wherein the system includes: a module operable to provide a representation of an echo signal that is indicative of a response over time to an interrogation signal of the body part, an electronic circuit operable, or configurable with software, firmware, or microcode, to fit the echo signal by a time model function that models an evolution over time of the echo signal, the time model function including a combination of a time circulation function that models a contribution over time of the circulation of the contrast agent to the echo signal, an immobilization function that represents the immobilization of the contrast agent, and a time decay function that models a decay over time of the echo signal from the immobilized contrast agent, and the electronic circuit operable, or configurable with software, firmware, or microcode, to estimate at least one kinetics indicator of the contrast agent from the time model function.