“…Gallstones invariably greater than 6 mm and those between 3 and 6 mm almost always display typical intense echoes and posterior acoustic shadowing. Highly attenuating stones tend to have a large percentage of crystalline material, a large crystal size, and more rigid structure (50). Occasionally, a stone greater than 3 mm fails to cast a shadow, and according to Gonzalez and MacIntyre (51)) shadowing depends primarily on orientation of the stone in relation to the sound beam.…”