A modeled study for diagnosis of small anechoic masses with ultrasound.

Hemispherical holes created in the bases of uniform natural sponges were imaged in water to determine how anechoic masses fill in with echoes at increased gains. The increase in gain, from the threshold for outlining a hole, to the fill-in of the hole with echoes, was obtained for a range of hole diameters and imaging conditions. These gain changes fit on a smooth curve when plotted against the hole diameter divided by the ultrasound beam width. The main sources of fill-in, beam width and multiple reverberations, appear to behave similarly in vivo. Understanding these effects may help reduce diagnostic errors.