The effect of focus size and intensity on stone fragmentation in SWL on a piezoelectric lithotripter

Julian Veser, Victoria Jahrreiss, Christian Seitz, Mehmet Özsoy, Julian Veser, Victoria Jahrreiss, Christian Seitz, Mehmet Özsoy

Abstract

Purpose: We aim to analyze the efficacy of different focus sizes and the influence of pulse pressure (intensity) during shock wave lithotripsy (SWL) in terms of stone fragmentation.

Methods: Combination of three focal sizes (F1 = 2 mm, F2 = 4 mm, F3 = 8 mm) and 11 output pressure settings (intensity 10-20) of a piezoelectric lithotripter (Wolf PiezoLith 3000) were tested on artificial stones (n = 99). The stones were placed within a 2 mm mesh cage. The needed number of shockwaves (SW) to first visible crack, 50% and 100% stone disintegration were recorded.

Results: Similar number of SW's were observed until the first crack 10, 11 and 11 SW's for F1, F2, and F3, respectively (p > 0,05). The median number of SW needed for 50% stone disintegration was 245 for F1 group, 242 for F2 group and 656 for F3 group. F1 vs F2 p = 0.7, F1 vs F3 and F2 vs F3 p < 0.05. Similarly, with larger focus size a higher number of shockwaves were necessary for 100% stone disintegration. 894, 877 and 1708 SW's for F1, F2 and F3, respectively. Only for F1 vs F3 and F2 vs F3 (all p < 0.05) a statistical difference was observed. These findings were consistent in all different power settings, with an increased difference in lower power levels (≤ 14).

Conclusions: A smaller focus size, as well as a higher peak pressure results in a more effective stone fragmentation. However, these results need to be confirmed in an in vivo setting with multiple parameters interfering the efficacy, like BMI, respiration or stone migration.

Keywords: Focus size; Fragmentation; SWL; Shock wave therapy; Urolithiasis.

Conflict of interest statement

The authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
a SWL-therapy head with mounted test device. b Artificial stone and mesh holder
Fig. 2
Fig. 2
Mean number of shock waves (y-axis) for each focus group (F1–F3, color coded) in correlation to the intensity level (10–20, x-axis)

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