Maximizing mechanical stress in small urinary stones during burst wave lithotripsy

Unlike shock wave lithotripsy, burst wave lithotripsy (BWL) uses tone bursts, consisting of many periods of a sinusoidal wave. In this work, an analytical theoretical approach to modeling mechanical stresses in a spherical stone was developed to assess the dependence of frequency and stone size on stress generated in the stone. The analytical model for spherical stones is compared against a finite-difference model used to calculate stress in nonspherical stones. It is shown that at low frequencies, when the wavelength is much greater than the diameter of the stone, the maximum principal stress is approximately equal to the pressure amplitude of the incident wave. With increasing frequency, when the diameter of the stone begins to exceed about half the wavelength in the surrounding liquid (the exact condition depends on the material of the stone), the maximum stress increases and can be more than six times greater than the incident pressure. These results suggest that the BWL frequency should be elevated for small stones to improve the likelihood and rate of fragmentation. (C) 2021 Acoustical Society of America.

Automated summary

Burst wave lithotripsy (BWL) uses tone bursts for treatment, and it was found that at low frequencies, the maximum principal stress is approximately equal to the pressure amplitude, while at higher frequencies, the maximum stress can increase significantly. It is recommended to increase the BWL frequency for small stones to improve the likelihood of fragmentation.