Theoretical analysis of local attenuation approximations when calculating scatterer correlation length

Determining the correlation length of ultrasound scatterers has shown potential in many tissue characterization applications. Accurate estimates of scatterer correlation length can only be obtained after correcting for focusing, frequency-dependent attenuation along the propagation path (total attenuation), and frequency-dependent attenuation in the region of interest (local attenuation). In order to correct for the local and total attenuation, an approximation is required because uncertainties in tissue attenuation can easily be 0.5 dB/cm-MHz, or greater, even for the same tissue type [J. Acoust. Soc. Am. 64, 423 (1978)]. Earlier simulation results demonstrated that the most robust approximation for the local attenuation while completely compensating for total attenuation and focusing for weakly focused sources was to assume a finite frequency dependence of ∼0.8 dB/cm-MHz independent of the true attenuation of the tissue for attenuation values between 0.05 and 1 dB/cm-MHz. The goal of the present study was to investigate the theoretical basis for this approximation so that the results could be applied to other ranges of attenuation values. The theoretical analysis was then compared to the simulation results to validate the conclusions. [This work was supported by the University of Illinois Research Board and the University of North Dakota School of Engineering and Mines.]