Harmonic amplitude distribution in a wideband ultrasonic wavefront after propagation through human abdominal wall and...

The amplitude characteristics of ultrasonic wavefront distortion produced by transmission through the abdominal wall and breast is described. Ultrasonic pulses were recorded in a two-dimensional aperture after transmission through specimens of abdominal wall or breast. After the pulse arrival times were corrected for geometric path differences, the pulses were temporally Fourier transformed and two-dimensional maps of harmonic amplitudes in the measurement aperture were computed. The results indicate that, as the temporal frequency increases, the fluctuation in harmonic amplitudes increases but the spatial scale of the fluctuation decreases. The normalized second-order and third-order moments of the amplitude distribution also increase with temporal frequency. The wide range variation of these distribution characteristics could not be covered by the Rayleigh, Rician, or K-distribution because of their limited flexibility. However, the Weibull distribution and especially the generalized K-distribution provide better fits to the data. In the fit of the generalized K-distribution, a decrease of its parameter alpha with increasing temporal frequency was observed, as predicted by analysis based on a phase screen model.