Application of Shock Waves and Pressure Pulses in Medicine

Abstract

Since 1980 extracorporeal shock waves and pressure pulses are used to disintegrate kidney stones. Since then, ESWL --- Extracorporeal Shock Wave Lithotripsy --- is the most important treatment for kidney stones. In the past years, more medical applications for these special pulsed acoustic waves were developed, e.g. for orthopedic pain therapy (ESWT --- Extracorporeal Shock Wave Treatment). Shock waves and pressure pulses have high peak pressures (up to 150 MPa) and very short time duration, typically 2--5 s. They are mostly generated by one of three principles: The electrohydraulic (spark gap) source, the electromagnetic (EMSE) source or the piezoelectric source. Some thousand pulses are released at a slow rate. They propagate through water into the body of the patient by an acoustic coupling means. In order to achieve the intended medical effects, they are focused on the treatment site. A number of physical parameters can be attributed to the effects of the pulses both on stones and tissue, the most important being the effective acoustic energy and the energy flux density. Stone disintegration is governed by direct wave effects, squeezing and cavitation. The waves also act on tissue, which may cause healing effects, but also some side effects. Targeting and treatment control is usually done by imaging systems using x-rays or ultrasound imaging. The result of the treatment can be described by efficiency quotients, which comprise stone-free rate as well as side effects.