Correlation between twinkling artifact and color Doppler carrier frequency: preliminary observations in renal calculi.

Color Doppler twinkling is a well-defined but not well-understood phenomenon that may assist in the detection of renal calculi. However, the relationship between the appearance of color Doppler twinkling and color Doppler carrier frequency has not been described systematically. To evaluate this relationship, a retrospective review was performed on 20 cases of renal calculi detected by twinkling on renal color Doppler sonography and confirmed with unenhanced computed tomography. The variable strength of twinkling at and behind renal calculi was observed with color Doppler carrier frequencies ranging from 1.75-4.0 MHz. All 20 calculi (100%) demonstrated twinkling when a low color Doppler carrier frequency, 1.75 or 2 MHz, was applied, whereas 12 of 20 cases (60%) were absent of twinkling when the highest carrier frequencies tested-3.5 or 4 MHz-were used. Quantitatively, there was a significant correlation between the amount of twinkling and carrier frequency (p = 0.002102). Hence, we conclude that the strength of the twinkling is color Doppler carrier frequency-dependent. The strength of the twinkling significantly increased when the color carrier frequency used for imaging decreased. Therefore, to improve renal calculi detection by enhancing the strength of the twinkling, the use of a lower color Doppler carrier frequency is recommended.