Bubbles trapped on the surface of kidney stones as a cause of the twinkling artifact in ultrasound imaging

A twinkling artifact (TA) associated with urinary calculi has been described as rapidly changing colors on Doppler ultrasound. The purpose of this study was to investigate the mechanism of TA. Doppler processing was performed on raw per channel radio-frequency data collected when imaging human kidney stones in degassed water. Suppression of twinkling by an ensemble of computer generated replicas of a single received signal demonstrated that the TA arises from variability among the acoustic signals and not from electronic signal processing. This variability was found to be random in nature, and its suppression by elevated static pressure, and its return when the pressure was released, suggests that the presence of surface bubbles on the stone is the mechanism that gives rise to the TA. Submicron size bubbles are often trapped in crevices on solid objects, but the presence of these bubbles in vivo is unexpected. To further check this mechanism under conditions identical to in vivo, stone-producing porcine kidneys were harvested en bloc with a ligated ureter and then placed into a pressure chamber and imaged at elevated atmospheric pressure. The result was similar to in vitro. [Work supported by NIH DK43881, DK092197, RFBR, and NSBRI through NASA NCC 9-58.]