Non-circular multi-sector split-focus transducer for coagulation therapy

The split-focus approach has a potential to substantially improve the throughput of coagulation HIFU treatment through multiplying the volume of the focal zone without forming unwanted foci either in front or behind the focal plane. The ideal, theoretically simplest split focal field can be generated from a geometrically focused transducer with a circular aperture uniformly divided into many sectors. However, for an intracavitary transducer, a non-circular shape of aperture is usually needed to have a necessary aperture area within its allowed size. A theoretical consideration how to divide the aperture into many sectors for forming a relatively uniform temperature distribution in the focal zone was developed. A transrectal therapeutic transducer at 3 MHz with a rectangular aperture of 20 mm × 40 mm divided into eight sectors with a geometric focal length of 30 mm was designed and fabricated based on the above consideration followed by the computer simulation of transient temperature distribution. It has been confirmed that significantly large lesion can be created even without tissue boiling if a spilt focus method is used with properly designed large number of sectors.