ACOUSTIC NONLINEARITY FOR TISSUE CHARACTERIZATION

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This proposal is a collaborative project between the members of the Ultrasonic and Magnetic Resonance Imaging Laboratories and the Department of Pathology at the Mayo Foundation. The overall goal of this project is to obtain insight into the mechanisms that interrelate acoustic nonlinearity and sound speed parameters of tissues to their intrinsic properties, and to exploit this information to construct images that display the intrinsic properties of tissues, viz., its composition. We have previously made extensive measurements of acoustic nonlinearity parameter (B/A) and sound speed (c) in excised human tissues and numerous model liquids. On the basis of these measurements we have established that the magnitude of these acoustic parameters relate quantitatively to the volume fractions of the constituents of tissues. Also, we have shown that these parameters can be used with the aid of mathematieal modeling to elueidate the physical state of water in tissues. The implication of these results is that any specific disease process that changes tissue composition should be detectable by observing the changes in the magnitude of these acoustic parameters. That is, B/A and in are suitable candidates for the purpose of tissue characterization and imaging. The current proposal consists of three specifie aims: 1) to validate the hypothesis that the 1 phenomena that give rise to acoustic nonlinearity or, are responsible for finite sound speed, occur due to perturbations at molecular level and less likely at the cellular level; 2) to develop, implement and evaluate three different methods (frequency mixing, amplitude modulation and pulse reversal) to make images of the nonlinearity parameter; and 3) to use mixture laws and acoustic data to construct images of tissues displaying two-dimensional distributions of the composition of tissues.