A new high intensity focused ultrasound applicator for surgical applications

Improved high-intensity focused ultrasound (HIFU) surgical applicators are required for use in a surgical environment. We report on the performance an d characteristics of a new solid-cone HIFU applicator. Previous HIFU device s used a water-filled stand-off to couple the ultrasonic energy from the tr ansducer to the treatment area. The new applicator uses a spherically-focus ed element and a solid aluminum cone to guide and couple the ultrasound to the tissue. Compared with the water-filled applicators, this new applicator is simpler to set up and manipulate, cannot leak, prevents the possibility of cavitation within the coupling device, and is much easier to sterilize and maintain during surgery. The design minimizes losses caused by shear wa ve conversion found in tapered solid acoustic velocity transformers operate d at high frequencies. Computer simulations predicted good transfer of long itudinal waves. Impedance measurements, beam plots, Schlieren images, and f orce balance measurements verified strong focusing and suitable transfer of acoustic energy into water. At the focus, the -3 dB beam dimensions are 1. 2 mm (axial) X 0.3 mm (transverse). Radiation force balance measurements in dicate a power transfer efficiency of 40%. In vitro and in vivo tissue expe riments confirmed the applicator's ability to produce hemostasis.