P1B-8 Experimental Investigation of the Effects of Gas Pockets on HIFU Field

The paper describes experimental and numerical studies of the effects of gas pockets on HIFU filed. Spherical air bubbles ranging from 1.5 to 5.0 mm diameter were produced in transparent polyacrylamide tissue mimicking gels. A single element 3.5 MHz HIFU transducer was used for sonication of the gel phantoms. Diffused backlight visualization technique was used to observe lesion formation in the tissue models. The changes in the HIFU beam pattern for air bubbles at different positions were visualized by schlieren method. Quantitative measurement of pressure at the HIFU focus by a calibrated needle hydrophone showed considerable reduction in the focal pressure with the presence of a pre-focal air pocket. The effects were simulated numerically and good agreement with experiments was obtained. The results provide guidelines for evaluation of potential safety concerns produced by trapped gas- pockets in various HIFU therapies.