Experimental temperature monitoring and coagulation detection using ultrasound-stimulated acoustic emission

Due to the high variability of tissue effects during sonication, temperature monitoring is one of the most crucial components for accurate thermal treatment of tissues with focused ultrasound (FUS) and other thermotherapy devices. Since the technique of ultrasound-stimulated acoustic emission (USAE) depends on the acoustic and mechanical properties, which both vary with temperature, it is hypothesized that the USAE signal is also temperature-dependent and in such a way that it can be used to guide thermal therapy. Therefore, in this paper, the dependence of USAE on tissue temperature is determined. In a series of experiments, where the same transducer is used for heating and USAE application, porcine muscle and fat samples are exposed to ultrasound at acoustical power levels of 6.6, 10.6 and 17.2 W over a period of 60-200 s that induce temperature elevation. In both tissue types, below the coagulation threshold, the USAE amplitude was found to vary quasi-linearly with temperature. However, at higher powers resulting in temperature above 55/spl deg/C that is beyond the coagulation threshold the correlation with temperature was lost due mainly to the irreversible nature of the changes in the tissue properties.