CASE REPORT

30         SA JOURNAL OF RADIOLOGY • March 2006

The ‘twinkling sign’ is described as a colour Doppler artifact in which a 

rapidly changing mixture of red and blue colours is displayed distal to a 

strongly, rough reflective structure (Figs 1 and 2).1 This probably results 

from complex back scatter of the ultrasound waves with prolonged pulse 

duration, interpreted by Doppler as movement.2 This sign is a funda-

mental artifact because it is well detected by the digital Doppler system 

which has a higher noise immunity.  The focal depth minimally affects 

the shape of the artifact by narrowing its focal width when the calculus 

is out of focus.1

There is a relationship between this artifact and the morphology 

(surface) and the chemical composition of the calculus. Identification 

of the composition of the calculus can help for the management options 

used.2

An artifact on other imaging modalities, which results from an 

error in the imaging technique, may lead to misinterpretation of the 

image.  The ‘twinkling sign’ may lead to misinterpretation by suggesting 

vascular flow. This particular artifact has a benefit in differentiating a 

very small calculus from other echogenic structures in the urinary tract 

particularly after lithotripsy.1,2 Another application of the twinkling sign 

is for guiding transthoracic needle aspiration of lung and mediastinal 

masses.  The needle is identified by using the twinkling sign (by mov-

ing the inner stylet gently). The needle tip is well located and the blood 

vessels are avoided.3

 1.   Aytac SK , Ozcan H. Effect of color Doppler system on the twinkling sign associated with urinary calculi.   

J Clin Ultrasound 1999; 27: 433-439.

2.   Darge K.  Be aware and beware of the twinkling sign.  Pediatr Radiol 2005; 35: 351-352

3.   Gorguner M, Misirlioglu F, Polat P, et al. Color Doppler  sonographically guided transthoracic needle 

aspiration of lung and mediastinal masses.  J Ultrasound Med 2003; 22: 703-708.

A useful ultrasound artifact and its application 
– the ‘twinkling sign’

H Lameen, MB ChB

S Theron, MB ChB, MMed (Rad)

F Steyn, MB ChB

M Grobbelaar, MB ChB

A Mapukata, MB ChB

S Andronikou, MB BCh, FRCR, FCRad, PhD

Department of Radiology, Tygerberg Hospital and University of Stellenbosch

PICTORIAL INTERLUDE

Fig. 1 (a) B- mode ultrasound of the left kidney shows two echogenic structures in the lower pole without acoustic shadowing. Applying the colour Doppler for the 
same kidney (b) shows multi-coloured  pixels, the 'twinkling sign', distal to the echogenic structures.

a useful ultrasound artifact.ind30   30 3/27/06   2:22:19 PM