A computational comparison of ultrasonically induced tissue heating between circular and rectangular transducer apertures

A comparison of theoretical tissue heating due to unscanned circular and rectangular focused ultrasound transducers has been performed. For comparison purposes, the same aperture area of π cm² and source power of 100 mW were used and the radius of the curvature for the rectangular aperture was the same as that for the circular case. The rectangular aperture was focused in the image plane and unfocused in the elevational direction. A homogenous-tissue model was used, and perfusion was taken into consideration. The temperature profile was generated by first calculating the relative field intensity values. These intensity values were then scaled to represent the same source power output for all constant-area transducer cases. Then the steady-slate pointsource solution of the bio-heat transfer equation was applied to determine the spatial thermal contribution for each field intensity value. By using superposition, the magnitude of the axial temperature was determined. For an aspect ratio of one, where the rectangular aperture is a square, the maximum temperature increase is approximately the same as that for the circular aperture. In general, the maximum temperature increase is greater for the circular source under these conditions.