Investigating the potential for thermal damage posed by microbubble ultrasound contrast agents: Experimental results
Stride E., Saffari N., Wilkens V.
Previous studies of the heating enhancement produced by microbubble ultrasound contrast agents have focused on the risks posed by unencapsulated bubbles. The results from theoretical simulations by the authors, however, indicate that the temperature rise due to viscous dissipation in the microbubble coatings may be sufficient to generate harmful bio-effects even under conventionally "safe" insonation conditions. The aim of this work was to make a preliminary experimental examination of the heating effect generated by contrast agents under diagnostic imaging conditions. Fine wire metal resistance thermometers were embedded in an agar block, with the wire tips protruding into a central cylindrical cavity into which suspensions of different types of microbubble agent (Optison®, Levovist® and Expancel®) could be injected. The results indicate that such agents do produce a measurable temperature rise under typical diagnostic conditions, which is of the same order of magnitude as that predicted theoretically. There are a number of areas of uncertainty, including the degree to which the sound field was modified by the presence of the contrast agent. If the validity of the results is confirmed by future experiments, however, there may be significant implications for the validity of existing safety guidelines. It may also be of interest for therapeutic applications in which enhanced heating is beneficial, e.g. ultrasonic ablation of tumours. © 2005 IEEE.