Abstract
Colour or power Doppler US examinations of a strongly echogenic and reflective structure can elicit the formation of an artefact distal to this structure at the site one normally expects to find an acoustic shadow. This artefact presents in colour Doppler as multi-pixel, multi-coloured, meteorite-tail-shaped configuration, commonly known as the 'twinkling sign'. Spectral Doppler at this site does not yield any flow. The two current hypotheses regarding the formation of the twinkling artefact are complex beam reflection interpreted by the Doppler as movement and intrinsic machine noise ('phase jitter'). The use of the twinkling sign as an additional diagnostic tool of concrements and calcifications has been evaluated in a number of in vitro and adult clinical studies. There is a lack of reports about the application of the twinkling sign in children. In this pictorial essay an array of colour Doppler ultrasound (US) images of urolithiasis in children is presented, featuring various facets of this US diagnostic tool. There are a number of technical parameters of an US machine that have a major influence with regards to inducing the twinkling artefact. The use of low frequency transducer combined with very high setting of the pulse repetition frequency seems to give the best result. The twinkling sign can be helpful in detecting small and obscured concrements, and may also have potential in characterization the type of stone. It is essential to gain more experience in the paediatric population on the twinkling sign and evaluate its usefulness in enhancing the sonographic diagnosis of urinary calculi thus curtailing the number of X-ray examinations, and consequently the radiation exposure.
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