Duplication artifacts can be created through diffraction and refraction on interfaces, also if the acoustical impedances of tissue is too much different and the ultrasound is reflected multiple on tissue layers, where the detected echo does not come from the shortest sound path.

See also Mirror Artifact.

Diffraction is the change in the directions and intensities of a group of sound waves after passing by an obstacle or through an aperture.

See also Acoustic Shadowing, Triplication Artifact and Duplication Artifact.

The refraction is the change of the sound direction on passing from one medium to another. In ultrasound, refraction is due to sound velocity mismatches combined with oblique angles of incidence, most commonly with convex scanheads. When the ultrasound wave crosses at an oblique angle the interface of two materials, through which the waves propagate at different velocities, refraction occurs, caused by bending of the wave beam.

See also Refraction Artifact, Acoustic Shadowing, Acoustic Mismatch, and Duplication Artifact.