Aliasing phenomenon (ultrasound)
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Aliasing is a commonly encountered artifactartefact in colorcolour and spectral Doppler ultrasound, which is caused by blood flow velocity exceeding the upper limits of the scale set by the user 1. The maximum velocity that can be displayed is limited by the pulse repetition frequency (PRF). If the PRF is too low, this results in a "wraparound" effect.
In spectral Doppler
In case of spectral Doppler the velocity peak is cut off at the peak of the scale, and the peak is displayed at the bottom of the scale, often overlapping with the rest of the curve. The artifact can be quickly remedied by lowering the baseline (if display of flow away from the transducer is not required), or increasing the PRF. Less frequently, increasing the Doppler angle might also become necessary 2.
In colorcolour Doppler
In colorcolour Doppler aliasing is encountered as red to blue hues immediately adjacent to each other in a vessel, which is - unlike in case of true flow reversal - not separated by a black region of no flow. The artifactartefact immediately disappears if the upper margin of the velocity scale is increased above the peak flow velocity. ColorColour aliasing is useful for detecting foci of increased flow (e.g. stenosis, arteriovenous fistula). Note that aliasing does not occur with power Doppler, as it does not display velocity 2.
-<p><strong>Aliasing</strong> is a commonly encountered artifact in color and spectral Doppler ultrasound, which is caused by blood flow velocity exceeding the upper limits of the scale set by the user <sup>1</sup>. The maximum velocity that can be displayed is limited by the <a href="/articles/pulse-repetition-frequency">pulse repetition frequency</a> (PRF). If the PRF is too low, this results in a "wraparound" effect.</p><h5>In spectral Doppler</h5><p>In case of spectral Doppler the velocity peak is cut off at the peak of the scale, and the peak is displayed at the bottom of the scale, often overlapping with the rest of the curve. The artifact can be quickly remedied by lowering the baseline (if display of flow away from the transducer is not required), or increasing the PRF. Less frequently, increasing the Doppler angle might also become necessary <sup>2</sup>.</p><h5>In color Doppler</h5><p>In color Doppler aliasing is encountered as red to blue hues immediately adjacent to each other in a vessel, which is - unlike in case of true flow reversal - not separated by a black region of no flow. The artifact immediately disappears if the upper margin of the velocity scale is increased above the peak flow velocity. Color aliasing is useful for detecting foci of increased flow (e.g. stenosis, arteriovenous fistula). Note that aliasing does not occur with power Doppler, as it does not display velocity <sup>2</sup>. </p>- +<p><strong>Aliasing</strong> is a commonly encountered artefact in colour and spectral Doppler ultrasound, which is caused by blood flow velocity exceeding the upper limits of the scale set by the user <sup>1</sup>. The maximum velocity that can be displayed is limited by the <a href="/articles/pulse-repetition-frequency">pulse repetition frequency</a> (PRF). If the PRF is too low, this results in a "wraparound" effect.</p><h5>In spectral Doppler</h5><p>In case of spectral Doppler the velocity peak is cut off at the peak of the scale, and the peak is displayed at the bottom of the scale, often overlapping with the rest of the curve. The artifact can be quickly remedied by lowering the baseline (if display of flow away from the transducer is not required), or increasing the PRF. Less frequently, increasing the Doppler angle might also become necessary <sup>2</sup>.</p><h5>In colour Doppler</h5><p>In colour Doppler aliasing is encountered as red to blue hues immediately adjacent to each other in a vessel, which is - unlike in case of true flow reversal - not separated by a black region of no flow. The artefact immediately disappears if the upper margin of the velocity scale is increased above the peak flow velocity. Colour aliasing is useful for detecting foci of increased flow (e.g. stenosis, arteriovenous fistula). Note that aliasing does not occur with power Doppler, as it does not display velocity <sup>2</sup>.</p>
References changed:
- 1. Pozniak MA, Zagzebski JA, Scanlan KA. Spectral and color Doppler artifacts. (1992) Radiographics : a review publication of the Radiological Society of North America, Inc. 12 (1): 35-44. <a href="https://doi.org/10.1148/radiographics.12.1.1734480">doi:10.1148/radiographics.12.1.1734480</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/1734480">Pubmed</a> <span class="ref_v4"></span>
- 2. Rubens DJ, Bhatt S, Nedelka S, Cullinan J. Doppler artifacts and pitfalls. (2006) Radiologic clinics of North America. 44 (6): 805-35. <a href="https://doi.org/10.1016/j.rcl.2006.10.014">doi:10.1016/j.rcl.2006.10.014</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/17147988">Pubmed</a> <span class="ref_v4"></span>
- 1. Pozniak MA, Zagzebski JA, Scanlan KA. Spectral and color Doppler artifacts. (1992) Radiographics 12 (1): 35-44.
- 2. Rubens DJ, Bhatt S, Nedelka S, Cullinan J. Doppler artifacts and pitfalls. (2006) Radiologic clinics of North America. 44 (6): 805-35.
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