ACOUSTIC NONLINEARITY PARAMETER TOMOGRAPHY FOR BIOLOGICAL SPECIMENS VIA MEASUREMENTS OF THE 2ND HARMONICS

The acoustic nonlinearity parameter B/A is a new parameter in ultrasou nd tissue characterization. In this paper, on the basis of a theoretic al analysis of finite amplitude ultrasonic wave propagation in fluidli ke media, an experimental system for nonlinearity parameter tomography is developed. Using this system, the amplitude of the second harmonic wave cumulated in the propagation path of the primary wave is measure d and the finite amplitude insert-substitution method is used in the c onventional computer tomography (CT) technique. The filtered convoluti on algorithm is implemented using the amplitude of the second harmonic as the projection data, then the B/A tomography can be reconstructed. The B/A images for several biological samples are obtained. Besides, the image of porcine pathological liver tissue is studied and is compa red with that of porcine normal liver tissue. These results show the p otential applications of the nonlinearity parameter B/A in medical dia gnosis. (C) 1996 Acoustical Society of America.