THE RELATION BETWEEN DIFFERENT SYSTEM GAIN SETTINGS AND THE ACCURACY OF DENSITOMETRIC ASSESSMENT OF ECHOGENICITY

Two mathematical transformations of the measured density of a sonograp hic image of the fetal liver were used in 19 patients at nine differen t system gain settings (G) (optimal G number [dB] and optimal G number +/- 2, +/- 4, +/- 8, +/- 12). A significant correlation was found bet ween the film-corrected density (D-cor) and gain interval from the opt imal gain (D-cor = 1.39 - 0.052 [G interval], R = -0.81, P < 0.00001, 95% confidence limits = -0.052 +/- 0.052). After standardization of th e values to the arbitrary G number of 49 (D-cor 49), a gain-independen t convergence of the values was found. In 79% of the 19 cases the accu racy of the method was very high, as estimated from a small coefficien t of variation. No significant difference was found in comparing the m ean standardized densities derived from paired measurements (i.e., opt imal G number +/- 2, +/- 4, +/- 8, and +/- 12). The data support backg round assumptions for the quantitative assessment or echogenicity by t ransmission densitometry and provide highly confident accuracy estimat es.