Measurement and Analysis of Impulse Source Produced by Ballistic Shock Wave Therapy Device in Different Medium Using PVDF Sensor

Purpose Radial extracorporeal shock wave therapy (rESWT) has been used in clinical and rehabilitation fields. However, the formulation of related clinical treatment protocols and the full potential of its therapeutic efficacy are constrained due to limited understanding of shock wave sources. This study aimed to further clarify the characteristics of shock wave sources generated at different medium interfaces. Methods Shock wave generated by rESWT device at the interface of different media (soft tissue-mimicking-phantom, water and air) was measured based on flexible polyvinylidene fluoride (PVDF) sensors. The temporal and spectral characteristics of the shock wave source were analyzed. Results The wave generated at the phantom interface was similar to that at the water interface under the same impact pressure, both being largely different from that at the air interface, where the absolute value of the peak pressure was significantly reduced. The spectral properties of the shock wave generated in different media were similar, with distinct peak frequencies, varying modulation frequencies in phantom (12.2 kHz), water (8.5 kHz), and air (7.2 kHz), and a relatively constant carrier frequency (between 82 and 83 kHz). Under the different impact pressures, there were no variations in the peak frequency at the same medium interface, indicating that the impact pressure mainly impacts the shock wave amplitude, but not the peak frequency. Conclusion The shock waves generated at different medium interfaces exhibited temporal and spectral differences. Therefore, measurement results in biological soft tissues cannot be simply replaced by the measurement results in air or water. The results of this study are expected to provide important information for evaluating rESWT devices and optimizing clinical shock wave treatment protocols.