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 substantially immobilized on a biological target, wherein the system includes: means for providing an echo signal indicative of a response over time to an interrogation signal of the body part, means for associating the echo signal with a model function of time modeling an evolution over time of the contrast agent in the body part, the model function including a combination of a circulation function modeling the circulation of the contrast agent and a decay function modeling a decay of the echo signal from the immobilized contrast agent, and means for estimating at least one kinetics indicator of the contrast agent from the model function.