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Concerning the non-thermal effects of ultrasound: a. In general, non-inertial cavitation is not a big problem in ultrasound b. The risk of cavitation is increased in the presence of micro bubble contrast media c. In the presence of micro bubbles, there is a risk of cavitation while scanning with a mechanical index (MI) in excess of 1.0 d. Organs at risk of cavitation-related damage in the absence of contrast media include the intestine and lungs both in the prenatal and postnatal period e. Acoustic streaming has the potential to cause tissue damage with an MI above 2.0 |
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Answer» a. True. Non-inertial (stable) cavitation is an oscillation of a pre-existing bubble subject to a pressure wave. It develops over several cycles and would require insonation with a continuous ultrasound wave held in one position, which rarely happens in practice. Inertial (transient) cavitation (growth and collapse of a bubble within a few cycles creating shock waves and an extreme local temperature rise) has more potential for damage. b. True. c. False. Such a risk exists at an MI above 0.7. d. False. In an aerated lung, there is indeed a risk of cavitation-induced haemorhage (e.g. during transoesophageal scanning). As the fetal lung is not aerated, it is not prone to such damage. e. False. Acoustic streaming (movement of fluid along an ultrasound beam, or ‘quartz wind’) is unlikely to cause adverse effects. |
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