Intervening attenuation affects first-order statistical properties of ultrasound echo signals

Previous studies show that first-order statistical properties of ultrasound echo signals are related to the effective number of scatterers in the "res olution cell" of a pulse-echo ultrasound system. When the effective number of scatterers is large (similar to 10 or more) this results in echo signals whose amplitude follows a Rayleigh distribution, with the RF echo signal o beying Gaussian statistics; deviation from Rayleigh or Gaussian statistics yields information on scatterer number densities. In this paper, the influe nce of the medium's attenuation on non-Gaussian properties of the echo sign al is considered. Preferential attenuation of higher frequency components o f a pulsed ultrasound beam effectively broadens the beam and increases the resolution cell size. Thus, the resultant non-Gaussian parameter for broad bandwidth excitation of the transducer depends not only on the scatterer nu mber density but also on the attenuation in the medium. These effects can b e reduced or eliminated by using narrow-band experiments.