Twinkling Artifact in Stone Diagnosis: Practical Application in Ultrasound Imaging
Physical Nature of the Artifact
The twinkling artifact (twinkling sign) is a rapidly changing mixture of red and blue colors recorded in color and power Doppler behind a strong reflector. The mosaic coloring occurs in the acoustic shadow of the stone due to surface irregularities and is not related to actual blood flow (EFSUMB Course Book, 2024; Hagen-Ansert, 2023).
Technique and Optimization
Color and power Doppler are more sensitive to twinkling when using 'all-digital' signal processing technology due to increased color sensitivity and acoustic power (Hagen-Ansert, 2023). In mammology, it has been shown that the artifact is more visible when the focal zone is set below the reflecting surface; pulsed Doppler allows differentiation of true blood flow from the artifact (Diagnostic Imaging: Breast, 2019).
Clinical Application in Stones
In typical renal colic, kidney stones are detected with a sensitivity of over 90% (EFSUMB, Ultrasound of the kidneys and ureter, 2020). Searching for twinkling is especially useful because small stones in the ureter are difficult to visualize in B-mode. The examination is conveniently started in the prone position, scanning the first few centimeters to the iliac bone, then moving to the pre-vesical spaces and the area of intersection with large vessels. Stones are often detected thanks to the twinkling artifact, and only then is the typical hyperechoic signal revealed, sometimes with a very thin acoustic shadow or none at all (EFSUMB, 2020).
When detecting a kidney stone, obstruction should be assessed: in obstruction, hydronephrosis is visualized, and the ureter may be dilated above the level of the obstruction. Normally, the ureter from the pelvi-ureteric junction to the bladder is not visualized unless dilated (Hagen-Ansert, 2023).
Features and Limitations
The mosaic color signal appears in the shadow of the stone due to surface irregularities; the artifact is usually not observed in stones composed of calcium oxalate (EFSUMB Course Book, Ultrasound of the renal vessels, 2024). The twinkling artifact as an alternative to native CT in patients with ureteral stones was studied in a prospective study (Sen V. et al., Urolithiasis 2017). The artifact is nonspecific for stones and can occur behind any strong specular reflector — microcalcifications, biopsy clips, corpora amylacea (Diagnostic Imaging: Breast, 2019; Prostate Ultrasound, 2015).
Differential Diagnosis of Bladder Inclusions
| Sign | Interpretation |
|---|---|
| Mobility + acoustic shadow | Stone |
| No shadow, blood flow present | Tumor |
| No shadow, no blood flow, mobile | Clot |
| Fixed to wall, shadow present | Wall calcification |
| Hyperechoic at anterior wall with reverberation | Air |
Frequently asked questions
What does the twinkling artifact look like?
A rapidly changing mosaic mixture of red and blue colors in color or power Doppler behind a stone, unrelated to blood flow (Hagen-Ansert, 2023; EFSUMB, 2024).
Why is twinkling especially useful for ureteral stones?
Small stones in the ureter are very difficult to visualize in B-mode; stones are often detected thanks to the twinkling artifact, and only then is the hyperechoic signal revealed (EFSUMB, Ultrasound of the kidneys and ureter, 2020).
How to optimize the visualization of the artifact?
Color and power Doppler are more sensitive when using 'all-digital' processing; the focal zone is recommended to be set below the reflecting surface (Hagen-Ansert, 2023; Diagnostic Imaging: Breast, 2019).
Is twinkling specific for stones?
No. The artifact occurs behind any strong reflector — microcalcifications, biopsy clips, corpora amylacea. Pulsed Doppler helps differentiate true blood flow (Diagnostic Imaging: Breast, 2019; Prostate Ultrasound, 2015).
In which stones might the artifact be absent?
The artifact is usually not observed in stones composed of calcium oxalate (EFSUMB, Ultrasound of the renal vessels, 2024).