Figure 1d. Twinkle artifact behind a bladder calculus. (a) Longitudinal post-voiding US image of the bladder shows a hyperechoic, shadowing bladder calculus (arrow). (b) Transverse color Doppler US image shows twinkle artifact posterior to the stone. (c) Transverse power Doppler US image again shows the twinkle artifact. (d) Doppler spectrum shows noise.