Frequency-dependent attenuation-compensation functions for ultrasonic signals backscattered from random media.

Abstract

Estimations of scattering parameters, such as average scatterer diameter, from rf signals backscattered from random media (tissues) are made from the frequency dependence of the rf signal. The frequency dependence of the rf signal backscattered from the medium is seen in the normalized power spectrum. The normalized power spectrum is found by taking the squared magnitude of the Fourier transform of the rf signal gated over a region of interest and dividing by some reference spectrum. If the medium has a frequency-dependent attenuation then the shape of the normalized power spectrum will be affected by the frequency-dependent attenuation and the time duration of the gated signal. Not accounting for the frequency-dependent attenuation leads to poor estimations of scatterer parameters. Larger attenuation and longer time gates give poorer estimates of scatterer parameters without attenuation compensation. Several attenuation-compensation functions have been used to account for the attenuation losses to the normalized power spectrum. A new attenuation-compensation function is proposed and compared with the other attenuation-compensation routines. The new attenuation-compensation function is shown to give improved estimates over previous attenuation-compensation functions for scatterers that follow a Gaussian form factor.