Dual frequency high intensity focused ultrasound to accelerate hemostasis

Abstract

In acoustic hemostasis, cavitation appears to help emulsify and heat tissue to form a paste which seals lacerations. Our objective was to mix two frequencies to enhance cavitation, increase heat deposition, and accelerate hemostasis. A focused transducer (curvature 5 cm) with a 4.3-MHz center element (diameter 2 cm) and a 125-kHz outer annular element (inner and outer diameters, 3 and 5 cm) was engineered. This dual frequency transducer was used to create lesions in a transparent gel phantom and to induce hemostasis in five rabbits. Hemostasis time was determined with both frequencies (4.3 MHz at 620 W/cm2, 125 kHz at 4 W/cm2) and with the high frequency only (4.3 MHz at 620 and 780 W/cm2). In gels, dual frequency HIFU created larger, broader lesions than 4.3-MHz HIFU alone. Bubbles created by just low frequency could be seen and, with sufficient time, created small local lesions. In rabbits, hemostasis times (∼1 min for 25-ml/min bleeds) were decreased 20% with dual frequency compared to the 4.3-MHz wave alone at the same intensity or same total electrical power. Dual frequency mixing can enhance heat deposition and accelerate hemostasis by HIFU. [Work supported by NSBRI SMS00203, NIH Fogarty, ONRIFO, and NSF BES0002932.]