In medical ultrasound, a clean shadow is a type of artifact characterized by a sharp, anechoic (black) area behind a highly reflective or attenuating structure. This phenomenon occurs when sound waves are completely blocked by an object, preventing them from reaching deeper tissues. Common examples include shadows cast by gallstones, kidney stones, or calcifications, which appear as distinct, well-defined dark regions directly posterior to the object.
Understanding clean shadows is crucial for accurate ultrasound interpretation, as they indicate the presence of dense structures. Differentiating clean shadows from other artifacts, such as dirty shadows (which are less defined and often contain echoes), aids in precise diagnosis. Sonographers often adjust gain and focus to better visualize the structure causing the shadow, thereby enhancing diagnostic confidence.