Artefacts in musculoskeletal ultrasound

Artefacts in musculoskeletal (MSK) ultrasound (US) comprise artefacts that mimic an abnormality while scanning normal structures and artefacts that occur together with abnormal conditions at grey-scale and Doppler imaging. Some of these can be avoided by correct scanning technique while other artefacts are the result of inherent characteristics of different tissues which may help in making a correct diagnosis. The origin and examples of common grey-scale and power/colour Doppler artefacts in ultrasound are explained with particular reference to MSK ultrasound. The commonly encountered Doppler artefacts such as the flash/twinkle artefacts and pseudo flow artefacts and their importance for image interpretation are discussed. Anisotropy is the sonographic artefact that is direction dependent and can be mistaken for a partial tear while scanning a tendon or nerve. Aliasing and random noise are well known artefacts, which depend upon grey-scale and overall gain. Mirror image artefacts refer to any highly reflecting smooth surface which may act as an acoustic mirror. In rheumatology, the mirrors will nearly always be bone surfaces. Blooming artefact displays colour outside of a vessel and makes vessels appear larger. Artefacts can also be due to ultrasound beam characteristics (side-lobe artefact), multiple echoes (reverberation, comet-tail, and mirror artefacts), and attenuation errors and enhancement, among others. Not all artefacts are confusing or unwanted. Certain artefacts are beneficial in assisting with the diagnosis. A better understanding of proper imaging techniques will allow correction or minimization of many of these artefacts