REAL-TIME ASSESSMENT OF THE PARAMETER OF NONLINEARITY IN TISSUE USINGNONLINEAR SHADOWING

A real-time pulse-echo method for assessing tissue nonlinearity is pre sented. Here, tissue nonlinearity refers to the parameter of nonlinear ity, B/A, and not the frequency dependence of the attenuation. Our non linearity assessment method is based on two pulse transmissions per be am position. One pulse is transmitted at a high intensity that propaga tes nonlinearily and, the other, at a low level, that propagates linea rly. Echo data are used to estimate a function representing the decay of fundamental frequency amplitude due to nonlinearity along the ultra sound path. This function is then mapped into an image that includes s hadows which relate to the nonlinearity of the preceding regions. To d elineate a region of interest from the background tissue, a normalizat ion curve is defined and used to compensate for the nonlinearity of th e background tissue. Experiments are performed on a tissue-mimicking p hantom and in vitro tissue samples including regions of high nonlinear ity. Results indicate that the method can effectively identify nonline ar regions and assess the extent of the nonlinearity. Copyright (C) 19 96 World Federation for Ultrasound in Medicine & Biology.