秋山 いわき¹, 西田 幸博¹, 中島 真人¹, 油田 信一², 伊藤 貴司³

Iwaki AKIYAMA¹, Yukihiro NISHIDA¹, Masato NAKAJIMA¹, Shinichi YUTA², Takashi ITOH³

¹慶応義塾大学理工学部電気工学科, ²筑波大学電子情報工学系, ³アロカ株式会社

¹Department of Electrical Engineering, Keio Univ., ²Institute of Information Science and Electronics, Univ. of Tsukuba, ³Aloka Co., Ltd.

キーワード : frequency dependent attenuation, broadband pulse, continuous wave, nonlinear relation, finite amplitude sound wave

　It is expected that biological tissues can be　characterized by the ultrasound transmission measurement of frequency dependent attenuation (F.D.A.) of the tissue　specimen. This method could be performed by comparing the amplitude of the transmitting wave with the incident wave at every frequency. Continuous sinusoidal wave has been utilized in the early works as a transmitting wave.　However, this technique is accompanied by the problem of the multiple reflection between the surface of　transmitting and receiving transducer and the　troublesomeness of changing the frequency over the wide range. Accordingly the method for determining F.D.A. at one shot by comparing the spectrum of a broadband RF pulse of the incident and transmitting wave has been recently become popular. We experimentally measured the attenuation vs. frequency curve by this technique and attained the nonlinear relation depending on the amplitude which is out of linear relation and never observed in the case of continuous wave experiment. As well as we found the　similar characteristics in some data of the previous other works.　We discussed this phenomenon by computer simulation and it is confirmed that this phenomenon results in the wave distortion according to a finite　amplitude sound wave propagation.