Ultrasound artifacts, explained

The machine assumes sound travels straight, at one speed, and bounces once. Artifacts appear when that isn’t true — and many of them are diagnostic.

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Acoustic shadowing

A dark band behind something that reflects or absorbs almost all sound: stones, bone, calcification. Gas gives a grey, “dirty” shadow.

Posterior enhancement

Fluid barely attenuates sound, but the machine still compensates as if it did, so tissue behind fluid looks brighter. It confirms that a black structure is fluid.

Reverberation

Sound bouncing between two strong reflectors appears as evenly spaced copies deeper on the screen — A-lines in the lung, or the ladder behind a needle.

Mirror image

A strong curved reflector such as the diaphragm–lung interface duplicates structures on the far side: liver appearing “above” the diaphragm is normal.

Edge shadows

Thin dark lines from the curved sides of round fluid-filled structures, caused by refraction. Harmless — not stones.

Real scans

Acoustic shadowing from a gallstone — A large calcified gallstone blocks the sound beam, leaving a black shadow behind it. — **Acoustic shadowing from a gallstone.** A large calcified gallstone blocks the sound beam, leaving a black shadow behind it. Hellerhoff · CC BY-SA 4.0 · source

Posterior acoustic enhancement — Sound passes easily through a fluid-filled renal cyst, so the tissue behind it looks brighter than tissue at the same depth. — **Posterior acoustic enhancement.** Sound passes easily through a fluid-filled renal cyst, so the tissue behind it looks brighter than tissue at the same depth. Kristoffer Lindskov Hansen, Michael Bachmann Nielsen and Caroline Ewertsen · CC BY 4.0 · source

Mirror-image artifact across the diaphragm — An echogenic liver haemangioma near the diaphragm is copied as a false 'mirror' image that seems to lie outside the liver. — **Mirror-image artifact across the diaphragm.** An echogenic liver haemangioma near the diaphragm is copied as a false 'mirror' image that seems to lie outside the liver. Hellerhoff · CC BY-SA 4.0 · source

Edge (lateral) shadowing and enhancement — Labels in the image: Gb = gallbladder, LS = lateral (edge) shadows from the curved walls, SV = enhancement behind the gallbladder, SA = shadowing. German labels are burned in. — **Edge (lateral) shadowing and enhancement.** Labels in the image: Gb = gallbladder, LS = lateral (edge) shadows from the curved walls, SV = enhancement behind the gallbladder, SA = shadowing. German labels are burned in. Kalumet · CC BY-SA 3.0 · source

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FAQ

Are artifacts always bad?

No. Shadowing diagnoses stones, enhancement proves a cyst, and lung ultrasound is built entirely on artifacts.

Related guides

A-lines vs B-linesThe difference between A-lines and B-lines on lung ultrasound, how many B-lines are abnormal, and what they mean — with real images and a live simulator.
Gallstones and cholecystitis on ultrasoundWhat gallstones look like on ultrasound (bright, shadowing, mobile), the signs of acute cholecystitis, and how to find the gallbladder. Interactive simulator and real scans.
Knobology: the four knobs that matterHow to set ultrasound gain, depth, focus and frequency — with a live simulator so you can turn the knobs and see what happens.

Educational content for learners; follow local protocols and supervision. Simulated images are generated by Sonoduck’s physics model; real images are credited individually.