Xi X, Zhong P
Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708, USA.
Ultrasound Med Biol. 2000 Mar;26(3):457-67. doi: 10.1016/s0301-5629(99)00124-6.
To control the collapse of cavitation bubbles induced during shock-wave lithotripsy (SWL), a piezoelectric annular array (PEAA) shock-wave generator was fabricated and combined with an experimental electrohydraulic (EH) shock-wave lithotripter with a truncated HM-3 reflector. The PEAA generator consists of eight individual transducers of 200-kHz resonant frequency. At a discharge voltage of 15 kV, the PEAA generator produces a shock wave with a peak positive pressure of 8.2 MPa, a positive half cycle duration of 2.9 micros, and a -6-dB beam width of 5 mm. The trigger of the PEAA generator was controlled via fiberoptic link with reference to the spark discharge of the EH generator. Hence, the PEAA-generated shock wave could be used to interact with cavitation bubbles induced by the EH source at various stages of their oscillation. The duration of bubble oscillation during SWL was monitored by a 2.25-MHz focused hydrophone, and this information was used to control the release timing of the PEAA generator. Stone fragmentation tests in vitro were carried out, and demonstrated that stone comminution could be significantly enhanced when the shock wave-bubble interaction occurred during the collapsing phase of the bubbles. A maximum increment of 60% to 80% in stone fragmentation was achieved when the PEAA-generated shock wave arrives near the collapse of the bubbles. Under these conditions, much intensified collapse of the bubbles near the surface of the stone, with strong secondary shock-wave emission and increased stress concentration at the impact site of the solid boundary, was observed using high-speed shadowgraph and photoelastic imaging.
为了控制冲击波碎石术（SWL）过程中诱导产生的空化气泡的塌陷，制造了一种压电环形阵列（PEAA）冲击波发生器，并将其与带有截短HM-3反射器的实验性电液压（EH）冲击波碎石机相结合。PEAA发生器由八个谐振频率为200 kHz的独立换能器组成。在15 kV的放电电压下，PEAA发生器产生的冲击波峰值正压为8.2 MPa，正半周期持续时间为2.9微秒，-6 dB波束宽度为5毫米。PEAA发生器的触发通过光纤链路参照EH发生器的火花放电进行控制。因此，PEAA产生的冲击波可用于与EH源在空化气泡振荡的各个阶段诱导产生的空化气泡相互作用。SWL过程中空化气泡振荡的持续时间由一个2.25 MHz的聚焦水听器监测，该信息用于控制PEAA发生器的释放时间。进行了体外结石破碎试验，结果表明，当冲击波与气泡的相互作用发生在气泡的塌陷阶段时，结石粉碎可得到显著增强。当PEAA产生的冲击波在气泡塌陷附近到达时，结石破碎量最大可增加60%至80%。在这些条件下，使用高速阴影图和光弹性成像观察到，结石表面附近的气泡塌陷大大加剧，伴有强烈的二次冲击波发射，并且在固体边界的撞击部位应力集中增加。
