Abstract
The potential for cardiac applications of HIFU remains unexamined. In order to create reproducible lesions in a beating heart, it is necessary to maintain focusing at a certain position within moving myocardial tissue. One technique is to use multiple short HIFU exposures (0.2 s) and synchronize them with an EKG signal and respiration. The left ventricular free wall (LVFW) of calf hearts were cut into 4-cm cubes, degassed in phosphate buffer saline (PBS), and heated to 37<th>°C. An 80-mm-diam spherical-cap transducer with a focus of 90 mm was operated at a frequency of 4.67 MHz and a nominal focal point intensity of 26.9 kW/cm2. The transducer was coupled to the LVFW using degassed PBS. First, the effect of pericardial fat, focal depth, and temperature on lesion size was individually evaluated. Then the 0.2-s HIFU exposure was applied 10 to 30 times at 4-s intervals. The same HIFU transducer was applied to an open-chest canine LVFW with the same triggering protocol. Dimensions of all lesions were measured by visual examination of the fresh, unstained tissue. A histopathological examination of the lesion was also performed. The in vivo lesions were created in similar size to those in vitro.
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