Shock Waves as Used in Biomedical Applications

Abstract

Basic textbooks generally describe shock waves produced by supersonic aircraft. This might be confusing to scientists from non-physical areas, because the relationship to clinical shock waves is not obvious. Other literature on shock waves frequently is specialized and written for readers with a solid background in physics. In this chapter, basic information on shock waves as used in biomedical applications is given. A main goal is to avoid confusions in regard to common definitions. Concepts such as peak-positive and peak-negative pressure, rise time, pulse duration, energy flux density, as well as different definitions of focal zones are explained. Emphasis is given on the fact that even if the physical parameters defined in this chapter may be useful to evaluate the output of pressure wave sources; there is still a debate on their correlation to therapy efficiency and biological effects. The differences between lithotripter shock waves and radial pressure waves, as used in orthopedics, traumatology, and other clinical applications, are also explained. This is specially important, because their modes of action and effects on living tissue may differ. Finally, a few systems to record pressure waveforms and cavitation events, such as polyvinylidene difluoride and fiber-optic hydrophones, as well as schlieren photography combined with photoelastic stress imaging, and passive cavitation detection, are described.