Evaluation of the soft tissue thermal index and the maximum temperature increase for homogeneous and layered tissues

Theoretical tissue temperature increases due to focused diagnostic ultrasound fields are evaluated for both homogeneous and three-layer tissue models. Applying the monopole-source solution, the general acoustic pressure field distribution is obtained for a specific source temporal average power. The axial steady-state temperature increase is calculated by applying the point-source solution of the bio-heat transfer equation to the pressure field distribution. Homogeneous and three-layer fetal tissue model examples for 3 MHz for circular source apertures are presented and compared to the thermal index of the recently approved Standard for Real-Time Display of Thermal and Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment