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[Ultrasonic tissue characterization of parotid tumors--analysis with the acoustic microscope].

The purpose of this study was to investigate acoustic properties of parotid tumors in detail by using the mechanically scanned acoustic microscope. The frequency of ultrasound was fixed at 200MHz. The amplitude images and the phase contrast images were taken in pictures. Mean attenuation, mean velocity, microscopic variation of the attenuation and that of the sound velocity were also measured and analyzed. The results are summarized as follows: 1) The acoustic properties of the tissue were optically displayed in the amplitude image and the phase contrast image. 2) The mean attenuation of malignant tumors was stronger than that of benign ones. 3) Microscopic variation of the attenuation was greater for malignant tumors than for benign ones. 4) No difference in velocity was found when malignant tumors and benign ones were compared as a whole, although the mean velocities are known to vary depending on the histological types. 5) The microscopic variation of the velocity was greater for malignant tumors than for benign ones. 6) Values of mean attenuation and mean velocity were strongly affected by the number of collagenous fiber. Microscopic variation of attenuation and that of velocity were affected by the arrangement of the tissue materials. 7) It is concluded that mean attenuation, mean velocity, microscopic variation of attenuation and that of velocity were useful parameters in investigating the acoustic properties of the tissue.