Range-Dependent Variance Artifacts in Narrow-Band Estimates of In Vivo Liver Attenuation

Abstmet-The attenuation coefficient in livers of 16 normal patients was estimated using a modified real-time sector scanner at 3 MHz and a narrow-band estimation technique. It was found that the estimates contained a range-dependent bias term, and that the variance of the estimate was positively correlated with the second spatial derivative of the beam-sensitivity profile beyond the focus of the transducer. We have postulated a stochastic model that demonstrates a relationship between the variance of the estimate and the product of the variance of the abdominal wall thickness fluctuations and the second derivative of the axial beam sensitivity profile. The consequences and limitations of this model are discussed.