Multipoint temperature control during hyperthermia treatments: theory and simulation.

A real-time multipoint feedback temperature control system has been designed and implemented with an ultrasound phased-array applicator for hyperthermia. The control parameters are the total power available from the supply and the dwell times at a sequence of preselected heating patterns. Thermocouple measurements are assumed for temperature feedback. The spatial operator linking available heating patterns to temperature measurements is measured at the outset of the treatment and can be remeasured on line an adaptive implementation. A significant advantage of this approach is that the controller does not require a priori knowledge of either the placement of the thermocouples or the power distribution of the ultrasound heating patterns. Furthermore, the control loop uses a proportional integral (PI) gain in conjunction with a singular value decomposition (SVD) of the spatial transfer operator. This approach is advantageous for robust implementation and is shown to properly balance the power applied to the individual patterns. The controller also deals with saturation in the inputs without integrator windup and, therefore, without temperature overshoot. In this paper, we present the theoretical formulation and representative simulation results of the proposed controller. The control algorithm has been verified experimentally, both in vitro and in vivo. A subsequent paper describing these results and the practical implementation of the controller will follow.