A refractive artifact, also called a refraction artifact or edge artifact, occurs when the ultrasound beam changes direction as it passes through a boundary between tissues with different speeds of sound. This bending of the beam is analogous to how light bends when it enters water, and it causes the ultrasound machine to misplace structures in the image because it assumes the beam travels in a straight line. Common examples include duplication of structures, particularly at curved surfaces like the edge of a cyst or the gallbladder wall. The diaphragm crus can also produce refraction artifacts that mimic aortic dissection flaps. Recognizing refractive artifacts prevents sonographers from misinterpreting them as real anatomic findings.