山越 芳樹, 森 英一, 佐藤 拓宋

Yoshiki YAMAKOSHI, Eiichi MORI, Takuso SATO

東京工業大学　総合理工学研究科

Graduate School at Nagatsuta, Tokyo Institute of Technology

キーワード : Low frequency vibration, Probing ultrasonic wave, Elastic properties of soft tissues

An imaging system which can observe the precise movements inside the tissues when the forced vibration is applied is proposed. In this system, the low frequency sinusoidal vibration of the frequency from 10 Hz to 1 KHz is applied from the surface of the tissues and the resulting movements at any desired points are measured by using the simultaneously transmitted probing ultrasonic waves. When the scatterers inside the tissues move sinusoidaly by the forced vibration, the ultrasonic waves reflected from these scatterers are subjected frequency modulation by the doppler effect. The index of the frequency modulation m_f is the function of the amplitude of the vibration, hence the amplitude can be estimated by measuring m_f of the received ultrasonic signals. In our method, the modulation index is estimated from the spectral components of the output signals of the quadrature detector. By using the system, we may estimate the elastic properties of the tissues from the propagation way of the low frequency vibration. Basic experiments are carried out by using 3.5 MHz ultrasonic waves. The accuracy of the proposed method is evaluated by comparing the estimated values of the proposed method with the values measured by using the optical displacement meter. Two dimensional images which show the distribution of movements inside the samples are shown for some phantoms as well as a few in vivo images.