Non-invasive monitoring of ultrasound phased array hyperthermia and surgery treatments

The use of high-intensity focused ultrasound for cancer therapy and tissue ablation has been receiving increased attention recently. Feedback for these treatments has been limited to invasive fine-wire thermocouple arrays. These are impractical in many clinical situations. For this purpose, a new non-invasive feedback method for ultrasound thermotherapy has been developed which is based on the estimation of a fundamental frequency f₁. The value of f₁ is a function of the average scatterer spacing and the local value of the speed of sound in the tissue, both of which are functions of temperature. It is computed from an A-line which is acquired using pulse-echo diagnostic ultrasound imaging the tissue zone being heated. Experimental results demonstrating quantitative, non-invasive temperature change measurements caused by a 192-element ultrasound phased array, as well as the underlying mathematical model, are shown.