Browsing by Author "Sapozhnikov, Oleg A."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Improving burst wave lithotripsy effectiveness for small stones and fragments by increasing frequency: theoretical modeling and ex vivo study
    (Liebert, 2022) Bailey, Michael R.; Maxwell, Adam D.; Cao, Shunxiang; Ramesh, Shivani; Liu, Ziyue; Williams, James Caldwell, Jr.; Thiel, Jeff; Dunmire, Barbrina; Colonius, Tim; Kuznetsova, Ekaterina; Kreider, Wayne; Sorensen, Mathew D.; Lingeman, James E.; Sapozhnikov, Oleg A.; Biostatistics, School of Public Health
    Introduction and Objective: In clinical trial NCT03873259, a 2.6-mm lower pole stone was treated transcutaneously and ex vivo with 390-kHz burst wave lithotripsy (BWL) for 40 minutes and failed to break. The stone was subsequently fragmented with 650-kHz BWL after a 4-minute exposure. This study investigated how to fragment small stones and why varying BWL frequency may more effectively fragment stones to dust. Methods: A linear elastic model was used to calculate the stress created inside stones from shock wave lithotripsy (SWL) and different BWL frequencies mimicking the stone’s size, shape, lamellar structure, and composition. To test model predictions about the impact of BWL frequency, matched pairs of stones (1-5 mm) were treated at 1) 390 kHz, 2) 830 kHz, and 3) 390 kHz followed by 830 kHz. The mass of fragments greater than 1 and 2 mm was measured over 10 minutes of exposure. Results: The linear elastic model predicts that the maximum principal stress inside a stone increases to more than 5.5 times the pressure applied by the ultrasound wave as frequency is increased, regardless of composition tested. The threshold frequency for stress amplification is proportionate to the wave speed divided by the stone diameter. Thus, smaller stones may be likely to fragment at higher frequency, but not lower frequency below a limit. Unlike with SWL, this amplification in BWL occurs consistently with spherical and irregularly shaped stones. In water tank experiments, stones smaller than the threshold size broke fastest at high frequency (p=0.0003), whereas larger stones broke equally well to sub-millimeter dust at high, low, or mixed frequency. Conclusions: For small stones and fragments, increasing frequency of BWL may produce amplified stress in the stone causing the stone to break. Using the strategies outlined here, stones of all sizes may be turned to dust efficiently with BWL.
  • Thumbnail Image
    Item
    The role of trapped bubbles in kidney stone detection with the color Doppler ultrasound twinkling artifact
    (IOP Publishing, 2018-01-09) Simon, Julianna C.; Sapozhnikov, Oleg A.; Kreider, Wayne; Breshock, Michael; Williams, James C.; Bailey, Michael R.; Anatomy and Cell Biology, IU School of Medicine
    The color Doppler ultrasound twinkling artifact, which highlights kidney stones with rapidly changing color, has the potential to improve stone detection; however, its inconsistent appearance has limited its clinical utility. Recently, it was proposed stable crevice bubbles on the kidney stone surface cause twinkling; however, the hypothesis is not fully accepted because the bubbles have not been directly observed. In this paper, the micron or submicron-sized bubbles predicted by the crevice bubble hypothesis are enlarged in kidney stones of five primary compositions by exposure to acoustic rarefaction pulses or hypobaric static pressures in order to simultaneously capture their appearance by high-speed photography and ultrasound imaging. On filming stones that twinkle, consecutive rarefaction pulses from a lithotripter caused some bubbles to reproducibly grow from specific locations on the stone surface, suggesting the presence of pre-existing crevice bubbles. Hyperbaric and hypobaric static pressures were found to modify the twinkling artifact; however, the simple expectation that hyperbaric exposures reduce and hypobaric pressures increase twinkling by shrinking and enlarging bubbles, respectively, largely held for rough-surfaced stones but was inadequate for smoother stones. Twinkling was found to increase or decrease in response to elevated static pressure on smooth stones, perhaps because of the compression of internal voids. These results support the crevice bubble hypothesis of twinkling and suggest the kidney stone crevices that give rise to the twinkling phenomenon may be internal as well as external.