Kang G et al, 2014: Characterization of the shock pulse-induced cavitation bubble activities recorded by an optical fiber hydrophone
Kang G, Cho SC, Coleman AJ, Choi MJ
Interdisciplinary Postgraduate Program in Biomedical Engineering, Jeju National University, 102 Jejudaehakno, Jeju-Si, Jeju Special Self-Governing Province, 690-756, Republic of Korea
KORUST Limited, B-#716,717, Keumkang Penterium IT Tower, 282 Hagui-Ro, Dongan-Gu, Anyang-Si, Gyeonggi-Do, 431-810, Republic of Korea
Medical Physics Department, Guy's and St. Thomas' National Health Service Foundation Trust, Lambeth Palace Road, London, SE1 7EH, United Kingdom
Department of Medicine, Jeju National University, 102 Jejudaehakno, Jeju-Si, Jeju Special Self-Governing Province, 690-756, Republic of Korea
A shock pressure pulse used in an extracorporeal shock wave treatment has a large negative pressure (less than -5 MPa) which can produce cavitation. Cavitation cannot be measured easily, but may have known therapeutic effects. This study considers the signal recorded for several hundred microseconds using an optical hydrophone submerged in water at the focus of shock pressure field. The signal is characterized by shock pulse followed by a long tail after several microseconds; this signal is regarded as a cavitation-related signal (CRS). An experimental investigation of the CRS was conducted in the shock pressure field produced in water using an optical hydrophone (FOPH2000, RP Acoustics, Germany). The CRS was found to contain characteristic information about the shock pulse-induced cavitation. The first and second collapse times (t1 and t2) were identified in the CRS. The collapse time delay (tc = t2 - t1) increased with the driving shock pressures. The signal amplitude integrated for time from t1 to t2 was highly correlated with tc (adjusted R(2) = 0.990). This finding suggests that a single optical hydrophone can be used to measure shock pulse and to characterize shock pulse-induced cavitation.
J Acoust Soc Am. 2014 Mar;135(3):1139-48. doi: 10.1121/1.4863199.
PMID:24606257 [PubMed - in process]
Shock wave pressure measurements by optical fibre hydrophones (FOPH) usually provide pressure signals which are well correlated with the real pressure profile of the shock wave within a time range of appr. 10 microseconds. Long lasting signal fluctuations are usually considered as distortions caused amongst others by cavitation and reflections within the fibre or the water basin. Shock pulse induced cavitation in water may last several hundred microseconds as being proved by Schlieren photographs. So far the signals may be considered cavitation-related. The interpretation of the signal as being related to the "first and second" collapse of cavitation bubbles seems to be doubtful since there are clouds of bubbles generated by the negative tail of the pressure profile with different size and very different collapse time, some lasting only a few microseconds other several hundreds of microseconds. Accordingly, a second collapse, if at all, would cover a wide period of time and would not appear in specific point of time as argued.