Demonstration of enhanced temperature elevation due to nonlinear propagation of focussed ultrasound in dog's thigh in vivo.

The results of an experimental study quantifying the temperature elevation gains produced by nonlinear propagation of focussed ultrasound fields in dogs' thighs in vivo are presented. Also, the intensity dependence of power absorption from a focussed ultrasound field was studied. The absorbed power appeared to elevate above intensities of 150-250 W cm-2 at 1 MHz in vivo. Enhanced temperature elevations were demonstrated at the same intensity levels, with the size of the elevation increasing with intensity. This phenomenon was large enough to be useful during focussed ultrasound hyperthermia since the maximum temperature gain was about 2 degrees C when a 5 degrees C temperature elevation was induced in the tissue. Using multiple overlapping beams, this effect was further increased.