Abstract

We present measurements from two SWT devices with different generating principles: an electrohydraulic source (EHS) with a focusing reflector (HMT Equitron) and a pneumatic source (PS) with no focusing (EMS Swiss Dolorclast). The acoustic field was measured with a PVDF membrane hydrophone. For the EHS the focal waveform consisted of a shock wave with a short compressive pulse lasting 1 μs (rise time less than 50 ns) and a negative tail of 1.5 μm. The average peak positive pressure at the focus was 20 MPa and showed little variation with energy level. The waveform from the PS had a compressive phase of 2-μm-duration (rise time 1 μs) followed by a complex negative phase of 4-μs duration. The peak positive pressure increased from 2 to 8 MPa with increasing energy setting. A passive cavitation detection (PCD) system was used to monitor the cavitation activity produced by the two devices. The EHS produced measurable cavitation with a life time that varied between 110 to 140 μs. We were unable to detect cavitation from the PS. These data indicate that the two devices studied here have different physical characteristics and this may affect the processes by which they operate clinically.

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