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. 2012 Apr;38(4):601-10.
doi: 10.1016/j.ultrasmedbio.2011.12.022.

Characteristics of the secondary bubble cluster produced by an electrohydraulic shock wave lithotripter

Yufeng Zhou  1 , Jun Qin, Pei Zhong
Affiliations

Characteristics of the secondary bubble cluster produced by an electrohydraulic shock wave lithotripter

Yufeng Zhou et al. Ultrasound Med Biol. 2012 Apr.

Abstract

This study investigated the characteristics of the secondary bubble cluster produced by an electrohydraulic lithotripter using high-speed imaging and passive cavitation detection techniques. The results showed that (i) the discrepancy of the collapse time between near a flat rigid boundary and in a free field of the secondary bubble cluster was not as significant as that by the primary one; (ii) the secondary bubble clusters were small but in a high bubble density and nonuniform in distribution, and they did not expand and aggregate significantly near a rigid boundary; and (iii) the corresponding bubble collapse was weaker with few microjet formation and bubble rebound. By applying a strong suction flow near the electrode tip, the production of the secondary shock wave (SW) and induced bubble cluster could be disturbed significantly, but without influence on the primary ones. Consequently, stone fragmentation efficiency was reduced from 41.2 ± 7.1% to 32.2 ± 3.5% after 250 shocks (p < 0.05). Altogether, these observations suggest that the secondary bubble cluster produced by an electrohydraulic lithotripter may contribute to its ability for effective stone fragmentation.

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Figures

Fig. 1
Fig. 1
Schematic diagram of the experimental setup in the Dornier HM3 lithotripter for pressure measurement, passive cavitation detection, high-speed shadowgraph and light transmission in a vertical view. A strong suction flow was applied close to the electrode tip to disturb the production of the secondary SW.
Fig. 2
Fig. 2
The waveforms of (a) the primary and (b) the secondary SWs at the geometric focal point of the HM3 lithotripter at the output voltage of 20 kV measured by fiber-optical probe hydrophone in the degassed water (O2 concentration <4 mg/L).
Fig. 3
Fig. 3
(a) A representative signal measured by the PCB transducer at the focal point of HM3 at the output voltage of 20 kV; (b) the dose dependency of the delay time between two SWs; (c) the comparison of dose dependency of the bubble collapse time both in the free field and near a solid boundary produced by the primary and secondary SWs; (d) the collapse strengths produced by the primary and secondary bubble clusters; and (e) the relationship of peak positive and negative pressures with output voltage. Twenty samples were recorded in each condition for statistical analysis.
Fig. 4
Fig. 4
Representative sequences of high-speed shadowgraphs of bubble dynamics (a) in a free field and (b) near a solid boundary produced by the primary SW, and (c) in a free field and (d) near a solid surface produced by the secondary SW in the focal region of the HM3 lithotripter at the output voltage of 20 kV. The number above each image frame indicates the time delay in μs after the trigger event. SW propagates from left to right and the frame size is about 12 × 9 mm.
Fig. 4
Fig. 4
Representative sequences of high-speed shadowgraphs of bubble dynamics (a) in a free field and (b) near a solid boundary produced by the primary SW, and (c) in a free field and (d) near a solid surface produced by the secondary SW in the focal region of the HM3 lithotripter at the output voltage of 20 kV. The number above each image frame indicates the time delay in μs after the trigger event. SW propagates from left to right and the frame size is about 12 × 9 mm.
Fig. 5
Fig. 5
Representative light transmission signal near a solid boundary in the HM3 at 22 kV with suction flow on and off.
Fig. 6
Fig. 6
(a) Comparison of the size distribution of fragments after 250 shocks at 22 kVat different suction pump status, and the representative photos of the treated stone fragments treated with (b) pump off and (c) pump on.
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