Ultrasonic imaging of the internal vibration of soft tissue under forced vibration

Abstract

To estimate the dynamic properties of soft tissues, an imaging system that can display both the amplitude and phase distributions of vibration in soft tissues under forced vibration was developed. In this method, low-frequency sinusoidal vibration with a frequency from 10 Hz to 1 kHz is applied from the surface of the sample, and the movement in it is measured using simultaneously transmitted probing ultrasonic waves. Then scatterers in the sample move sinusoidally under the forced vibration, and the reflected ultrasonic waves are subject to the frequency modulation by the Doppler effect. The amplitude of vibration is estimated from the frequency modulation index of the reflected waves. This is derived from the amplitudes of the spectrum components of the output of the quadrature detector of the received signal. On the other hand, the phase of vibration is estimated from the angle of the fundamental spectrum component. Basic experiments have been carried out using a 3.0-MHz ultrasonic wave system. The accuracy of the method is evaluated and two-dimensional color maps of the amplitude and phase are shown for several phantoms, as well as tissues, in vivo.