Feedback control of temperatures during hyperthermia treatments with phased-array ultrasound applicators

A feedback control algorithm has been developed for control of tumor temperatures during hyperthermia treatments performed with ultrasound phased-array applicators. The algorithm takes temperature measurements from invasive thermocouple probes, and uses both the amplitude and the dwell times applied to each of a set of pre-computed focal patterns for control. Hard limits on the control inputs (maximum power level, non-negative dwell times) are taken into account by the algorithm. Desired temperatures may be set for a subset of the measured temperatures, and the ultrasound heating of the tumor is controlled such that the actual temperatures are as close as possible (in a mean-squared sense) to the specified temperatures. Experimental results using this control algorithm during in-vivo ultrasound hyperthermia treatments of a canine cancer tumor are presented, demonstrating that the algorithm does not require prior knowledge of the position of the temperature sensors or of the heating distribution resulting from the focal patterns.