Comparison of the output display standard's TIS estimates with independently determined maximum temperature increase calculations

The monopole-source solution was used to calculate the three dimensional complex acoustic pressure field for focused circular apertures and transmit f-numbers from which the three-dimensional temperature distribution was calculated using the bio-heat transfer equation in homogeneous, perfused media. For the 184 cases, the acoustic field was normalized to the derated spatial peak, temporal average intensity of 720 mW/cm², the maximum value allowed by the United States Food and Drug Administration 510(k) diagnostic ultrasound equipment approval process, from which the axial temperature increase profile and the maximum temperature increase were determined. Also, from the normalized acoustic field, the soft-tissue thermal index (TIS) was determined according to the procedures of the Output Display Standards from the normalized acoustic field.