Analysis of Impulse Source Produced by Radial Shock Wave Therapy Device in Different Media Using Finite Element Method

Objective: Extracorporeal shock wave therapy (ESWT) has been widely used in clinical and rehabilitation fields. However, limited knowledge of shock wave sources constrains its therapeutic efficacy. This study aimed to simulate and analyze the characteristics of shock wave sources generated by the radial extracorporeal shock wave therapy (rESWT) device at different media interfaces. Methods: In this paper, a numerical calculation model including the front portion of the handpiece of an rESWT device and three different media (soft tissue, water, and air) was established using the finite element method, and the dynamic impact process was carried out according to the basic principle of the rESWT apparatus. The projectile speed was set to be 7.11, 12.46, 17.81 and 23.16m/s, respectively. In addition, the waveforms at the geometric center of the applicator surface were extracted, and the temporal and spectral characteristics of the shock wave source were disclosed. Results: The waveform of shock wave generated by the applicator of the rESWT device at soft tissue and water interface were similar at the same projectile speed, but both being different from the waveform at air interface. The absolute positive and negative pressure values at the air interface were three orders smaller than those observed at the soft tissue and water interfaces. The spectral characteristics of the waveforms at different media interfaces were similar, with modulation frequencies of soft tissue, water and air being 4.51 kHz, 3.97 kHz and 4.03 kHz, and carrier frequencies being 78.00 kHz, 76.90 kHz and 77.27 kHz, respectively. At different projectile speeds, there was no variation in the waveform shapes of the same medium, revealing that the projectile speed didn't affect the peak frequency of the shock wave waveform. The projectile speed only affected the amplitude of the shock wave waveform, indicating that the absolute positive and negative pressure at the medium interface increased linearly with the projectile speed. Conclusion: The shock waves produced at various media interfaces displayed changes in their temporal and spectral characteristics, and the results observed in biological soft tissues couldn't be directly substituted with those observed in air or water. The findings could offer crucial insights into the assessment of rESWT devices and the enhancement of clinical shock wave treatment protocols.