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Abstract: Shock wave therapy (SWT) refers to the use of focused shock waves for treatment of musculoskeletal indications including plantar fascitis and dystrophic mineralization of tendons and joint capsules. Measurements were made of a SWT device that uses a ballistic source. The ballistic source consists of a handpiece within which compressed air (1–4 bar) is used to fire a projectile that strikes a metal applicator placed on the skin. The projectile generates stress waves in the applicator that transmit as pressure waves into tissue. The acoustic fields from two applicators were measured: one applicator was 15 mm in diameter and the surface slightly convex and the second was 12 mm in diameter the surface was concave. Measurements were made in a water tank and both applicators generated a similar pressure pulse consisting of a rectangular positive phase (4 μs duration and up to 8 MPa peak pressure) followed by a predominantly negative tail (duration of 20 μs and peak negative pressure of −6 MPa), with many oscillations. The rise times of the waveforms were around 1 μs and were shown to be too long for the pulses to be considered shock waves. Measurements of the field indicated that region of high pressure was restricted to the near-field (20–40 mm) of the source and was consistent with the Rayleigh distance. The measured acoustic field did not display focusing supported by calculations, which demonstrated that the radius of curvature of the concave surface was too large to effect a focusing gain. Other SWT devices use electrohydraulic, electromagnetic and piezoelectric sources that do result in focused shock waves. This difference in the acoustic fields means there is potentially a significant mechanistic difference between a ballistic source and other SWT devices. (E-mail: robinc@bu.edu) [Copyright &y& Elsevier]

We report measurements of a number of different shock wave therapy (SWT) devices. Two devices were electrohydraulic (EH): one had a large shock source (HMT Ossatron) and the other was a small hand-held source (HMT Evotron). The other device was a pneumatically driven device (EMS Swiss Dolorclast) and two different hand pieces were measured, one with an ‘‘unfocused’’ head and the other with a ‘‘focused’’ head. We found that the EH sources generated focused shock waves with a positive phase about 1 microsec long and peak pressure around 40 MPa, however, the acoustic output of the HMT Evotron appeared to be independent of the power setting of the machine. For the pneumatic source the duration of the positive phase was greater than 4 microsec and the peak pressure about 7 MPa. There was no clear shock front present and the waveform had a complex tail structure that was dependent on the power setting of the machine. We found that the focused hand-piece did not generate a focused acoustic field. The results are compared to reports of measurements from electromagnetic SWT devices. We contrast measurements made with different hydrophone systems: fiber-optic probe hydrophone, PVDF membrane hydrophone and PVDF bullet-shaped hydrophone. [ABSTRACT FROM AUTHOR]