This is a proposal for continuation of R01-CA38515. During the first three years of this work we have demonstrated using in vitro work that statistically significant differences exist among the frequency slopes of acoustic attenuation of normal liver, mild liver disease and moderate/sever liver disease. Furthermore, when the frequency dependent attenuation behavior is modeled as a power-law, increasing fat and fibrosis content in the liver exhibited concomitant increase in the exponent of the power law; however, fat involvement resulted in increase in the proportionality constant as well. Recent literature in this field has reported difficulties in implementing attenuation estimation techniques in vivo. These difficulties stem from the need for appropriate corrections for beam diffraction and from distortions due to body wall. Inverse Diffraction Filtering (IDF) methods have not been very successful in reducing errors in the estimation due to their failure to account for body wall effects and the scattering properties of the tissues. We have demonstrated that an Axial Beam Translation method (ABT) is capable of effectively eliminating estimation errors due to diffraction. We propose to continue the investigation to demonstrate the feasibility of identification and followup of diffuse liver disease in vivo in terms of the acoustic attenuation parameters.
Our specific aims are: 1) Establish through computer simulations the optimal conditions under which Axial Beam Translation (ABT) produces the best estimates of the attenuation parameters in scattering media; compare these with estimates obtained via standard methods corrected with Inverse Diffraction Filtering (IDF). 2) Verify these optimal conditions in water tank experiments on known tissue mimicking phantoms and tissues. 3) Design and construct a sector scanning head system capable of both real time ABT and IDF measurement and extended focus imaging; incorporate this device into an experimental imaging ad measurement system. 4) Test the modified experimental system on normal volunteers and on patients undergoing evaluation for liver disease. Correlate results of attenuation estimations obtained via IDF and ABT methods with the pathological fat and/or fibrosis content of the liver.
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