Impact of nonlinear propagation on temperature distributions caused by diagnostic ultrasound

As interest in imaging of the harmonics generated by nonlinear propagation in tissue has grown, it has been recognized that the patterns of heat deposition in tissue may be altered with respect to those observed with the assumption of linear propagation. Changes in the patterns of heat deposition have been studied by the use of computer simulations. The generation of harmonic energy has been simulated by a solution of Burger´s equation by methods developed by Christopher and Parker. The bio-heat transfer equation has been solved by the method of finite differences. With these models, temperature differences that arise from assumed linear and nonlinear propagation have been made and the degree of greater potential of bioeffects have been made. Typically, nonlinear propagation moves the location of highest temperature increases closer to the transducer in soft tissue or to the bone surface in the fetal bone case. In some cases such as those where the acoustic beam travels through amniotic fluid, substantial increases (in the order of 50%) in temperature rise may occur. The impact of nonlinear propagation on regulatory models is discussed