Ultrasound artefacts

Acoustic Enhancement

Low attenuation behind a fluid-filled structure, commonly occurring behind cysts, bladder, gallbladder, or amniotic fluid. Fluid transmits sound better than surrounding tissue.

Acoustic Shadowing

High attenuation or reflection from a dense object, seen behind bones, gallstones, or bowel gas. Results in a dark shadow due to strong reflection or absorption of sound.

Reverberation

Repeated reflection of sound between two strong reflectors. It often appears near the anterior bladder wall or metallic objects, leading to multiple equally spaced echoes.

Speed of Sound Artefact

Occurs when tissue has a different sound speed than the assumed 1540 m/s, leading to displacement and distortion of structures on ultrasound.

Refraction

Bending of sound at tissue interfaces with different speeds and oblique angles, which leads to misplaced echoes, often encountered near muscle-fat interfaces.

Edge Shadowing (Refraction Shadowing)

Occurs at the curved edge of a structure due to refraction and beam divergence, seen at ovaries or kidneys, creating shadow-like areas beside the structure.

Mirror Image

Strong reflector causes the beam to bounce back from a false second location, common under diaphragm or pleura, producing a duplicated, deeper structure.

Aliasing

Doppler artefact that occurs when blood flow velocity exceeds the Nyquist limit, leading to incorrect display of flow with colour or spectral wraparound.

Comet Tail

Type of reverberation with very short path and strong reflectors, commonly seen with surgical clips or cholesterol crystals, creating a dense tapering tail of echoes.

Ring-Down

Similar to comet tail but caused by resonance of gas bubbles, seen in biliary tree or bowel gas, producing a long, bright tail extending from gas.