Fig. 16From: Quantitative ultrasound imaging of soft biological tissues: a primer for radiologists and medical physicistsVarious statistics may be computed on the echo envelope data within a region of interest. Prior to modeling with a probability density function (PDF), a histogram of the echo magnitude is computed within a specified region of interest. Two models with meaningful parameters can be used to fit the data: (1) the homodyned-K distribution (HDK), which is a general model with one scale parameter (the mean intensity μ) and two shape parameters (α and k); and (2) the Nakagami distribution, which is an approximate simpler model with one scale parameter (Ω) and a single shape parameter (m). As illustrated, changing the shape parameter(s) allow(s) modeling different forms of the image histogram corresponding to different backscatter tissue properties. PHK is the PDF of the fit with the HDK model; and PN is the PDF of the fit with the Nakagami modelBack to article page