Assessment of tissue nonlinearity using 'nonlinear shadowing' effect

A real-time pulse-echo method for assessing tissue nonlinearity is described. Echo data are used to estimate a function representing the decay of fundamental frequency component amplitude due to nonlinearity along the ultrasound path. This function is then mapped into an image that includes shadows which relate to the nonlinearity of the preceding regions, a phenomenon analogous to attenuation shadowing observed in the conventional B-mode images. Experiments are performed on a tissue mimicking phantom and in vitro tissue samples including regions of high nonlinearity. Results indicate that the method can effectively identify nonlinear regions and assess the extent of the nonlinearity.