Acoustical tissue nonlinearity characterization using bispectral analysis

A novel method for measuring the biological soft tissue nonlinearity from nonlinear propagation characteristics of low frequency vibration using bispectral analysis is proposed, The nonlinearity of the biological tissue is represented by an equivalent second order parameter of nonlinearity Gamma. By formulating the waveform distortion due to medium nonlinearity, this Gamma is represented as a function of the wave distortion (N) defined as the amplitude ratio of the third harmonics to the fundamental frequency components. In order for adequate estimation of N from the noisy vibrational waveform detected by ultrasonic pulse Doppler method, bispectral analysis which is immune to additive Gaussian noise was used, Measurement results of Gamma for pig tissue (pork) and human tissue both in vitro and in vivo will be shown.