Cavitations in biological tissues

Aim: An important reason for the high popularity of diagnostic ultrasound i s its lack of hazardous side effects. However, as described below, the prob ability of inducing undesirable thermal and mechanical effects in tissue in creases with a rise in the output of diagnostic ultrasound machines. Method s and Results: The use of increasing negative peak pressures of the applied ultrasound pulse enhances the risk of inducing cavitation inside the body. The potential damage of cavitation results from the dynamic, e.g. wild pul sation, and a collapse of bubbles in the respective sound field. The collap se, especially, releases a high amount of energy, related to secondary effe cts like shock waves, jet formation and the formation of free radicals. To estimate the likelihood of cavitation and ensuing mechanical biological eff ects the so-called mechanical index was defined. Nowadays, the mechanical i ndex is displayed in real-time on modern diagnostic ultrasound machines. Ec ho-contrast agents play an increasing role in sonography. These stabilised gas particles increase the likelihood of cavitation formation and the occur rence of other biological side effects. The potential for mechanically indu ced side effects of diagnostic ultrasound was tested in many animal studies . As for the use of ultrasound for diagnostic purposes, adverse side effect s, like haemorrhage or rupture of capillaries, were only observed in the pr esence of tissue-gas interfaces - as found in the lung or the intestine - o r with high concentrations of contrast media. Conclusion: Even though no ad verse effects of diagnostic ultrasound have been reported in humans, potent ially damaging effect of advanced ultrasound techniques cannot be denied. V arious ultrasound organizations, e.g. WFUMB, have therefore formulated reco mmendations for the safe use of diagnostic ultrasound.