Measurements of calf liver ultrasonic differential and total scattering cross sections

Abstract

Ultrasonic scattering from calf liver has been measured and normalized to obtain the average differential scattering cross section per unit volume σ̄sd (ν) over scattering angles ν ranging in magnitude from 25 ° to 165 ° and frequencies between 3 and 7 MHz. The results indicate that, at each of the measured frequencies, calf liver is a weak scatterer with nearly one-half of the total scattered power directed between 25 ° and 45 °. The value of σ̄sd (165 °) , which is not expected to differ much from σ̄sd (180 °) , the backscattering coefficient, was found to be approximately 3.7 × 10−6f1.4 mm−1Ω−1, with f in MHz and Ω in steradians. By integrating σ̄sd over all the measured scattering angles to find the total scattering cross section σ̄st , the contribution of scattering loss to attenuation was found to be approximately 2% over the measured frequencies. Analysis of the shape of σ̄sd suggests that the correlation length of the liver was on the order of 1 mm. To assess the accuracy of the normalization method, experimental and theoretical results for σ̄st of a reference medium consisting of glass spheres in agar were compared and found to differ by less than 10%.