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Sound speed scanning acoustic microscopy for biomedical applications.

Since 1985, we have been developing a scanning acoustic microscope (SAM) system for biomedical use and have been investigating the acoustic properties of various organs and disease states by using this SAM system. In biomedicine, SAM is useful for intraoperative pathological examination, study of low-frequency ultrasonic images, and assessment of biomechanics at a microscopic level. Recently, we have proposed a new concept -- acoustic microscopy -- using a single pulsed wave instead of continuous waves used in conventional SAM systems. In the present study, we compared two systems by measuring the same biological material. The sound speed image obtained by sound speed microscopy corresponded well to that obtained using a conventional SAM system. Lesions with hyaline degeneration showed a lower sound speed when compared with that of normal myocardium. Frequency domain analysis of amplitude and phase by both methods also showed similar characteristics. Although the data acquisition time of one frame was greater than that in conventional SAM, the total time required for calculation was significantly shorter. The SAM system can be applied to intraoperative pathological examination.