![]() It is worth remembering however, that not all renal stones will be associated with a twinkle artifact. This is especially true if the calculus is not associated with acoustic shadowing. Teaching point: The twinkle artifact improves sensitivity and specificity for the detection of small renal calculi. The movement may be caused by the patient’s respiration and transmitted arterial pulsation and/or slight unconscious movements of the probe. The machine misinterprets these changes as random Doppler shifts. My guess is that the first of these is correct, and that slight movement of the stone (or other structure) causes significant changes of the echo signal (because of the rough surface). – the cause is movement of the structures due to ultrasound radiation force. – the cause is small gas bubbles trapped on the rough surface (this comes from Jonathan Rubin’s group and doesn’t seem to be widely embraced by others) – the cause is “phase jitter” in the machine’s electronics (this seems improbable to me) – the key thing is that the structure causing the artifact has a rough surface I’ve come across four different theories, none of which seems to be widely regarded as the leading contender. The following comments are by Robert Gill, author of “The Physics and Technology of Diagnostic Ultrasound: A Practitioner’s Guide” regarding the origin of the twinkling artifact: Several papers have been published which try to address this issue. It is not yet clear what is the cause of the twinkling artifact. On the other hand, the twinkle artifact produced by the small non-shadowing stone in the VUJ was helpful in confirming the presence of the stone. 2 D imaging was clearly sufficient in this case to diagnose the large renal calculus. This has been observed in previous studies (7) as a potential misdiagnosis of blood flow. With our patient, colour Doppler behind the larger 14mm stone produced a colour artifact that resembled turbulent, aliasing / mosaic, blood flow. Rough surfaced rather than smooth surfaced stones produce this artifact (5) Not all stones produce a twinkling artifact. When the focal zone is located below a rough reflective surface, the twinkling artifact becomes more pronounced. It is dependent on the location of the focal zone.It is more pronounced when the reflective surface is rough.It is more sensitive (47.6 % to 86% in one study (4))and specific (1) for detection of small stones than is acoustic shadowing.It appears with or without a comet tail artifact.It has the appearance of turbulant blood flow.It is seen behind a reflective surface (such as a calculus).It is a focus of alternating colours on Doppler signal.This artifact is associated with several characteristics (2) The twinkling artifact was first descibed by Rahmouli et al in 1996 (3) This is due to spatial compounding which creates shadows at different angles that are averaged (1) Using colour Doppler to look for the twinkling artifact improves the ability to confirm the presence of small stones especially if an acoustic shadow is not present. When stones are small they may not produce characteristic posterior shadowing. Experienced radiologists attain the highest sensitivities and specificities for the identification of stones. Unfortunately, the visualisation of stones with ultrasound is operator dependent and therefore the sensitivity ranges between 19 -93% with a specificity of 84 -100%. In an uncomplicated case of renal colic, an ultrasound can help with diagnosis and disposition. The great advantage however is that sonography does not irradiate the patient especially in a group of patients who tend to have multiple CTs for the same pathology. Sonography of the renal tract to look for stones is not as sensitive or as specific as CT scanning. Why use Colour Doppler to help identify stones and what is the twinkling artifact?
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