Cavitation Biology and the Safety of Contrast-Aided Diagnostic Ultrasound

Contrast agents for diagnostic ultrasound consist of stabilized microbubbles designed to enhance the echogenicity of blood filled regions and reveal tissue perfusion. The availability of these agents has enabled the study of cavitation biology in diagnostic ultrasound, a topic of non-ionising radiation biology which was previously a matter of conjecture. Bioeffects are engendered by intermittent imaging at high peak rarefactional pressure amplitudes (PRPA), which nucleates cavitation within tissue capillaries and allows refill of the capillaries with agent between high PRPA images. The magnitude and extent of the bioeffects depends not only on the agent dosage and PRPA, but also on ultrasound timing parameters and tissue of interest. Cavitational bioeffects, which have been demonstrated using commercial contrast agents and diagnostic ultrasound in animal models, include heart capillary rupture with cardiomyocyte killing and kidney glomerular capillary haemorrhage into the urinary space with consequent acute tubular necrosis. The medical significance of such randomly scattered bioeffects is uncertain, but cardiac arrhythmia and hematuria are clinically detectable manifestations. The potential for cavitational biological effects, particularly with common patient conditions which migh