Lewin P A, Chapelon J Y, Mestas J L, Birer A, Cathignol D
Department of Electrical and Computer Engineering, Drexel University, Philadelphia, PA 19104.
Ultrasound Med Biol. 1990;16(5):473-88. doi: 10.1016/0301-5629(90)90170-h.
There is growing evidence that acoustic cavitation plays an important role in stone fragmentation during extracorporeal shock wave lithotripsy (ESL) treatment. In addition, side effects of the treatment, such as the hemorrhage and destruction of the tissue in the vicinity of the stone are also ascribed to cavitation phenomenon. Since cavitation is associated with the maximum negative pressure in the shock pulse, it would thus appear that possibility of controlling this pressure would be desirable in ESL applications. This paper describes a novel technique developed to control the ratio of compressional peak (P+) to rarefactional peak pressure (P-) of the shock wave for use in lithotripsy treatment. The procedure is based on the finite amplitude wave generation by focused piezoelectric transducers and subsequent interaction of the shocked waves in the common focal region. The highly asymmetrical shock wave is produced in the focal region by providing an appropriate time delay to each of the high voltage electrical excitation signals which drive the transducers. The degree of relative reduction of negative halfcycles and the corresponding positive halfcycles amplification increases with the number of the acoustic sources used. The practical implementation of the shock wave generator was obtained by using 5 cm diameter, focused 1 MHz transmitter, and additional transducers of identical construction having frequencies corresponding to the harmonics and subharmonics of the 1 MHz frequency. The importance of the results for the future development of lithotripters, and stone treatment efficiency is pointed out.
越来越多的证据表明，在体外冲击波碎石术（ESL）治疗过程中，声空化在结石破碎中起着重要作用。此外，该治疗的副作用，如结石附近组织的出血和破坏，也归因于空化现象。由于空化与冲击波中的最大负压有关，因此在ESL应用中控制该压力似乎是可取的。本文描述了一种为控制用于碎石治疗的冲击波的压缩峰值（P+）与稀疏峰值压力（P-）之比而开发的新技术。该过程基于聚焦压电换能器产生的有限振幅波以及随后在公共聚焦区域中冲击波的相互作用。通过给驱动换能器的每个高压电激励信号提供适当的时间延迟，在聚焦区域产生高度不对称的冲击波。负半周期的相对减小程度和相应正半周期的放大程度随着所用声源数量的增加而增加。通过使用直径5厘米、聚焦1兆赫兹的发射器以及具有与1兆赫兹频率的谐波和次谐波相对应频率的相同结构的附加换能器，实现了冲击波发生器的实际应用。文中指出了这些结果对碎石机未来发展以及结石治疗效率的重要性。
