Abstract: A system for the non-invasive inspection of a living organism utilizes two ultrasonic fields, one of which is produced by a perturbing beam transmitting transducer to perturb an internal region of tissue at a focal region which may be subject to movement. The second ultrasonic field consists of a set of ultrasonic beams, constituting a sense beam and reference beams, and which may be portions of a single beam or a plurality of separate beams and which are directed through and near the focal region of the perturbing field before and/or after perturbation. The time of flight differences of the sense beam and reference beams are detected by a plurality, preferably at least three, receiving transducers whose outputs are processed by a digital computer system, interacting with the signal analysis electronics, to derive information concerning the internal tissue of the living organism.