New method of estimating the ultrasonic beam ratio parameter for characterizing sound propagation in tissue

The backscattered ultrasonic signal from soft tissue can be considered to consist of two parts: a spatially fluctuating component due to coherent scattering from randomly distributed scattering centers and a relatively constant component related to structural ordering. The relationship between these, which has been termed the "beam ratio parameter" influences the speckle pattern of an ultrasound image. First-order image statistics for this special speckle pattern are characterized by the Rician distribution. Changes of second-order statistics have also been derived as a function of the beam ratio parameter. A new method for the estimation of the beam ratio parameter from the intensity distribution of the ultrasonic signal is described in this paper. This method was used to measure the parameter in ultrasonic images from phantoms and liver tissue yielding values of about 0.1. The measured changes of the second-order statistics were not correlated to this parameter. The results indicate that the relatively constant intensity component related to structural ordering has only a small influence on the speckle pattern.