Quantitative assessment of sonographic image echogenicity by transmission densitometry: fetal liver model

A mathematical method is proposed to compare density values of different sonographs of the same tissue. Two transformations were needed: (1) calibration of the gray scale according to the maximal range of scanning for a given tissue, and (2) comparison of the effect of two time-compensated gains on the difference in density and standardizing this effect to an arbitrary gain. To verify these relationships, 12 fetal livers were scanned at 38 weeks' gestation, at three different gains corresponding to the optimal gain and to the minimal and maximal gains that allowed a clear image to be obtained. After the mathematical transformations, the initially completely different densities were nearly identical (t-test: P = 0.9998; Wilcoxon test: P > 0.5; Pearson's R = 0.8933). This method permits an accurate quantitative assessment of the echogenicity of any parenchymatous organ.