Acoustic Impedance Profiling—an Experimental Model and Analytical Study with Implications for Medical Diagnosis
Acoustic parameter characterization in a quantitative manner of soft tissues in the human body leading to tissue typing is a potentially powerful method for clinical medicine for the identification and differentiation of disease entities in a non-invasive manner. This study is concerned with the determination of acoustic impedance profiles in physical models, some of which have impedance values in the range of body soft tissues. The physical models used are of a plane parallel face multilayer type, and the sound beam is at normal incidence to the plane face. Materials used in the model have been lucite, silastic rubber of varying compositions (to produce acoustic impedance differences of a few percent at a boundary) and ρc rubber. The sound beams used mostly have been those produced by focused transceivers (fundamental frequency 1MHz-2MHz) delivering a damped oscillatory wave. A more nearly unipolar pulse unfocused beam has also been used (supplied by Bolt, Beranek and Newman of Cambridge, Massachusetts under a subcontractual arrangement). The algorithms used for the study involve the determination of the impulse response of the medium; and from this impulse response, the impedance profile is computed.