Safety and bio-effects of ultrasound contrast agents

The use of gas-filled microbubbles as ultrasound contrast agents raises potential safety concerns for diagnostic ultrasound imaging. A number of biological effects have been seen in experimental systems, including the induction of physiological response to cardiac exposures (premature ventricular contractions) and damage at a microvascular level (microvascular rupture and petechial haemorrhage). The literature indicates that a mechanical index (MI) of 0.4 represents the threshold above which microvascular bio-effects are seen in in vivo studies. Above this value, the extent of biological effects appears to increase rapidly with both increasing in situ peak negative acoustic pressure amplitude and with contrast agent concentration. While there is no proven evidence of harm resulting from clinical use of these agents, caution is recommended when contrast-enhanced imaging is undertaken.