The effect of hypobaric pressure on the kidney stone twinkling artifact

Recently, our group proposed the color Doppler ultrasound twinkling artifact originates from stable crevice bubbles on the kidney stone surface because overpressure suppressed twinkling on ex vivo stones (Lu et al., Ultrasound Med. Biol. 2013). However, the hypothesis is not fully accepted because the bubbles were not directly observed. Here, the submicron-sized bubbles predicted by the crevice-bubble hypothesis are enlarged in ex vivo kidney stones by exposure to a pre-focal, off-axis lithotripter pulse (p₊ = 1.5 MPa, p_-=2.5 MPa) or hypobaric static pressures (0.021 MPa, absolute) to simultaneously capture their appearance by high-speed photography and ultrasound imaging. In rough stones that twinkle, consecutive lithotripter pulses caused more than 50% of bubbles to grow reproducibly from specific locations on the stone surface, suggesting the bubbles were pre-existing. Conversely, on smooth stones that did not twinkle, repeated lithotripter pulses initiated bubbles from varying locations on the stone surface. Similarly, upon exposure to hypobaric static pressures, the simple expectation that twinkling would increase by enlarging bubbles largely held for rough-surfaced stones but was inadequate for smoother stones. These results suggest a correlation between kidney stone surface topography or stable surface crevice bubbles and twinkling. [Work supported by NSBRI through NASA NCC 9-58 and NIH DK043881.]