Microbubbles on kidney stones contribute to the twinkling artifact in humans

The color Doppler ultrasound twinkling artifact, a rapid color change that highlights kidney stones, was recently attributed to surface crevice microbubbles on ex vivo stones because twinkling was affected by changes in hydrostatic pressure. However, it was unclear whether crevice bubbles existed on in situ human kidney stones, and, if so, how smooth-surfaced stones could harbor the crevice bubbles that give rise to twinkling. Here, 8 human subjects with known kidney stones were exposed to 4 atmospheres absolute (ATA) while breathing air inside a hyperbaric chamber; twinkling was monitored and quantified with a research ultrasound system. At 3 and 4 ATA, twinkling was significantly reduced by an average of 35% and 39%, respectively (p = 0.04). Then, ex vivo kidney stones that twinkled were exposed to micro-computed tomography (μCT) and hypobaric pressures while submerged in water. Regions of low x-ray attenuation within the stone (i.e., microcracks) at 1 ATA expanded when the pressure was reduced to 0.1 ATA. These results support the theory that microbubbles are present on kidney stones in the human body and that microbubbles may be internal as well as external to the kidney stone. [Work supported by NSBRI through NASA NCC 9-58 and NIH DK043881.]