Answer capsule: Ultrasound artifacts are image findings that do not accurately represent anatomy because an imaging-system assumption has been violated. For the SPI exam, identify the visual pattern, name the physical cause, and know the adjustment that can reduce it.
Ultrasound artifacts are a frequent SPI exam topic. Connect the visual pattern to a violated assumption: sound travels in a straight line, follows a direct path, travels at 1,540 m/s in soft tissue, and returns echoes from the expected location.
Reverberation versus comet-tail versus ring-down
Reverberation occurs when sound bounces repeatedly between strong reflectors. It commonly appears as multiple, equally spaced parallel echoes that become weaker with depth.
Comet-tail artifact is a short, bright, tapering reverberation-type artifact behind a small, highly reflective interface.
Ring-down artifact is different. It is a continuous echogenic band associated with resonance involving gas bubbles rather than ordinary discrete reverberation lines.
Common SPI ultrasound artifacts
| Artifact | Appearance | Cause |
|---|---|---|
| Reverberation | Repeated equally spaced lines | Multiple reflections between strong reflectors |
| Comet-tail | Bright, short, tapering trail | Closely spaced reverberation behind a small reflector |
| Ring-down | Continuous bright band | Resonance involving gas bubbles |
| Shadowing | Dark region behind a structure | Strong attenuation or reflection |
| Enhancement | Increased brightness behind a structure | Low attenuation through fluid |
| Mirror image | Duplicated anatomy across a strong reflector | An indirect reflected path is interpreted as straight |
| Refraction | Displaced or duplicated anatomy | Beam bending at an oblique interface |
| Side-lobe or beam-width | False echoes inside anechoic structures | Energy from secondary or wider beam paths |
Doppler aliasing as an artifact
Aliasing occurs in pulsed Doppler when the Doppler frequency shift exceeds the Nyquist limit, which is one-half of the pulse repetition frequency. The display may show flow in the wrong direction or wrap around the velocity scale.
Use the Nyquist limit calculator to connect imaging depth with PRF and the Nyquist limit. Also review the SPI physics formula sheet and ultrasound glossary.
Frequently asked questions
What is the difference between reverberation and comet-tail artifact?
Reverberation usually appears as repeated echoes between strong reflectors, often with equally spaced lines. Comet-tail artifact is a shorter, tapering reverberation-type artifact behind a small, highly reflective interface.
What is ring-down artifact?
Ring-down is a continuous echogenic band commonly associated with resonance involving gas bubbles. It is distinct from ordinary discrete reverberation lines.
What causes posterior acoustic shadowing?
Posterior acoustic shadowing occurs when a structure strongly attenuates or reflects the ultrasound beam, leaving reduced echoes behind the structure.