7.3 Ultrasound Artifacts in Vascular Imaging

7.3 Ultrasound Artifacts in Vascular Imaging

Artifacts are features in the image that do not correspond to actual anatomy or true flow. The scanner assumes sound travels in a straight line at exactly 1,540 m/s, attenuates uniformly, and returns directly to the transducer. When those assumptions break, predictable artifacts appear. Exam items describe an artifact and ask you to name it or to choose the maneuver that removes it.

Gray-scale and Doppler artifacts

Mirror image in detail

A mirror-image artifact most famously duplicates the subclavian artery beneath the highly reflective pleural surface, producing a phantom vessel with its own Doppler signal at a deeper, symmetric location. Mistaking the mirror for a real vessel can lead to an invented finding. The clue is symmetry across a bright reflector; changing the scan plane or angle makes the true vessel persist while the mirror weakens or disappears.

Why calcium is the technologist's nemesis

Dense calcified plaque is the most common practical artifact source in carotid and lower-extremity arterial work. It blocks the beam (shadowing), so velocities cannot be sampled at the point of maximal stenosis, and it can produce twinkle on color. The compensating strategy is to interrogate the vessel from multiple windows — anterior, lateral, posterior — and to grade stenosis using the highest velocity obtainable in an open segment plus indirect signs (post-stenotic turbulence, downstream waveform damping) when the throat is shadowed.

Recognizing flow artifacts

• Flash artifact is a burst of color from cardiac, respiratory, or transducer motion. It fills tissue with color where no vessel exists. Steadying the probe and raising the color write-priority or threshold suppresses it.
• Blooming is color spilling beyond the vessel wall from excessive color gain; reduce gain.
• Edge / refraction shadowing at the lateral walls of a vessel can mimic wall thickening; it is a refraction effect, not plaque.

Worked scenario

A technologist scanning a subclavian artery sees a second identical artery and pulsatile Doppler signal located symmetrically deep to a bright curved line. Recognizing the bright line as pleura and the duplicate as a mirror-image artifact, the technologist angles off the pleura; the phantom vessel disappears while the true subclavian remains. No deep accessory vessel is reported.

Common traps

• Reporting a mirror image as a real vessel or a duplicated jet as additional disease.
• Calling refraction edge shadowing wall thickening.
• Treating twinkle as flow — it is a color artifact behind calcium, not perfusion.
• Forgetting that shadowing hides the highest velocity, so a normal-looking sampled velocity can coexist with a severe shadowed lesion; rely on indirect signs.

Range ambiguity and propagation-speed errors

Two more artifacts arise from the scanner's timing assumptions. Range ambiguity occurs when a deep echo from one pulse returns after the next pulse has already been sent, so the machine places it too shallow; it is more likely at high PRF and deep imaging and is reduced by lowering PRF. A propagation-speed error appears when sound crosses tissue that does not travel at exactly 1,540 m/s (fatty tissue is slower); the scanner mis-times the return and displays the interface at the wrong depth, which can make a vessel wall look stepped or displaced.

Recognizing that these are timing artifacts, not anatomy, keeps you from reporting a phantom finding.

Enhancement and attenuation artifacts

Posterior acoustic enhancement is the bright zone deep to a fluid-filled structure such as a patent vessel lumen, cyst, or pseudoaneurysm, because fluid attenuates little and leaves more energy for deeper tissue. It is a useful confirmatory sign that a structure is fluid-filled rather than solid. Its opposite, edge shadowing, comes from refraction at the curved walls of a round vessel and produces thin dark lines off the lateral edges; novices mistake it for plaque.

The corrective step for both is to interpret them as expected physics and, when they obscure anatomy, to change the angle or window so the beam strikes the interface differently. Mastering this artifact catalog lets you separate genuine pathology from the predictable ways ultrasound lies.