Ultrasonic heating of the skull

Comparatively simple analysis shows that diagnostic ultrasound devices, in some cases, may approach output levels that can produce significant heating of tissues, particularly if the propagation path includes bone. The model assumes that all of the ultrasonic energy transmitted into the bone is converted into heat at the surface. The heat source, therefore, is a disk with diameter equal to the sound beam. Experimental tests of these predictions using rodents show that temperature increments of the order of 3°C/W/cm2 are produced in skull bone with sharply focused fields under medically relevant conditions. [This work was supported in part by U.S.P.H.S. Grant No. CA 39241.]