HARMONIC AMPLITUDE DISTRIBUTION IN A WIDE-BAND ULTRASONIC WAVE-FRONT AFTER PROPAGATION THROUGH HUMAN ABDOMINAL-WALL AND BREAST SPECIMENS

The amplitude characteristics of ultrasonic wavefront distortion produ ced 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 o f harmonic amplitudes in the measurement aperture were computed. The r esults indicate that, as the temporal frequency increases, the fluctua tion in harmonic amplitudes increases but the spatial scale of the flu ctuation decreases. The normalized second-order and third-order moment s 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 t heir limited flexibility. However, the Weibull distribution and especi ally the generalized K-distribution provide better fits to the data. I n the fit of the generalized K-distribution, a decrease of its paramet er a with increasing temporal frequency was observed, as predicted by analysis based on a phase screen model. (C) 1997 Acoustical Society of America.