WOLD decomposition of the backscatter echo in ultrasound images ofsoft tissue organs

摘要

Deals with a method of detecting and estimating the scatterernspacing between the regularly spaced resolvable coherent scatterers inntissue. Scatterer spacing has been successfully used in classifyingntissue structure, in differentiating between normal and cirrhotic liver,nand in detecting diffuse liver disease. This paper presents a WOLDndecomposition of the radio frequency (RF) field into its diffused andncoherent components from which maximum likelihood estimates (MLE) ornminimum mean square error (MMSE) estimates of the scattering spacing areneasily computed. The MLE are efficient and for relatively long recordnare unbiased. They result in accurate estimates in low signal-to-noisen(SNR) ratios. Unfortunately, they require nonlinear minimization andnknowledge of the probability density associated with the RF backscatternecho. The MMSE estimates, on the other hand, are computationally simple,nyield unique closed form solutions, do not require a-priori knowledge ofnthe probability distribution function of the backscatter echo, andnresult in accurate estimates in low SNR ratios. This paper also presentsnan unbiased decision rule to detect whether or not an RF echo exhibitsnany specular scattering relative to the wavelength of the interrogatingnultrasonic pulse. The approach has been tried on simulations as well asnon in-vivo scans of liver data, and appears to perform well