A system for characterizing tissue, comprising: a probe, to be hold against the body of a subject and that comprises a vibrator to deliver mechanical vibrations to a tissue of the subject; an ultrasound emitter that is configured to emit a sequence of ultrasound shots (80, 80', 80", 110, 110', 110") and an ultrasound receiver configured to receive corresponding echo signals; and a control module programmed to make the system executing the following steps: a) delivering a continuous and periodic mechanical vibration to the tissue of the subject, the periodic mechanical vibration comprising of a same vibration pattern repeated several times successively over time; b) emitting a sequence of ultrasound shots (80, 80', 80", 110, 110', 110") by means of the ultrasound emitter and acquiring corresponding echo signals received by the ultrasound receiver to track how the tissue is moved by the periodic mechanical vibration delivered to the tissue; c) providing homogeneity information (808, 808', 808", 809, 810, 811, 118a, 118a', 118a") to an operator of the system, the homogeneity information being determined from at least some of the echo signals acquired in step b), the homogeneity information being representative of the ability of the tissue to transmit elastic waves and of the homogeneity of the tissue with respect to the propagation of elastic waves; wherein the control module is programmed so that: - steps b) and c) are executed by the system continuously, several times successively, characterised in that the control module is further programmed so that: - the sequence of ultrasound shots (80, 80', 80", 110, 110', 110") emitted in step b) spans at least over one half of a same period of the periodic mechanical vibration delivered to the tissue, and comprises at least 10 ultrasound shots per period of said mechanical vibration. a probe, to be hold against the body of a subject and that comprises a vibrator to deliver mechanical vibrations to a tissue of the subject; an ultrasound emitter that is configured to emit a sequence of ultrasound shots (80, 80', 80", 110, 110', 110") and an ultrasound receiver configured to receive corresponding echo signals; and a control module programmed to make the system executing the following steps: a) delivering a continuous and periodic mechanical vibration to the tissue of the subject, the periodic mechanical vibration comprising of a same vibration pattern repeated several times successively over time; b) emitting a sequence of ultrasound shots (80, 80', 80", 110, 110', 110") by means of the ultrasound emitter and acquiring corresponding echo signals received by the ultrasound receiver to track how the tissue is moved by the periodic mechanical vibration delivered to the tissue; c) providing homogeneity information (808, 808', 808", 809, 810, 811, 118a, 118a', 118a") to an operator of the system, the homogeneity information being determined from at least some of the echo signals acquired in step b), the homogeneity information being representative of the ability of the tissue to transmit elastic waves and of the homogeneity of the tissue with respect to the propagation of elastic waves; a) delivering a continuous and periodic mechanical vibration to the tissue of the subject, the periodic mechanical vibration comprising of a same vibration pattern repeated several times successively over time; b) emitting a sequence of ultrasound shots (80, 80', 80", 110, 110', 110") by means of the ultrasound emitter and acquiring corresponding echo signals received by the ultrasound receiver to track how the tissue is moved by the periodic mechanical vibration delivered to the tissue; c) providing homogeneity information (808, 808', 808", 809, 810, 811, 118a, 118a', 118a") to an operator of the system, the homogeneity information being determined from at least some of the echo signals acquired in step b), the homogeneity information being representative of the ability of the tissue to transmit elastic waves and of the homogeneity of the tissue with respect to the propagation of elastic waves; wherein the control module is programmed so that: - steps b) and c) are executed by the system continuously, several times successively, characterised in that the control module is further programmed so that: - the sequence of ultrasound shots (80, 80', 80", 110, 110', 110") emitted in step b) spans at least over one half of a same period of the periodic mechanical vibration delivered to the tissue, and comprises at least 10 ultrasound shots per period of said mechanical vibration. - steps b) and c) are executed by the system continuously, several times successively, characterised in that the control module is further programmed so that: - the sequence of ultrasound shots (80, 80', 80", 110, 110', 110") emitted in step b) spans at least over one half of a same period of the periodic mechanical vibration delivered to the tissue, and comprises at least 10 ultrasound shots per period of said mechanical vibration.