Self-tuning fuzzy logic control for ultrasound hyperthermia with reference temperature based on objective functions

The purpose of this paper is to develop and evaluate a self-tuning fuzzy logic controller for a scanned focused ultrasound hyperthermia system with the reference temperature (T-r) determined from objective functions. This work employs simulation programs to develop the power deposition for the scanned focused ultrasound system and to solve the responses of temperature profiles based on the transient bioheat transfer equation. A fuzzy logic control algorithm is employed to determine the output power level for the heating system and an observer for blood perfusion variation is used to enhance the capability of the controller to adjust the required output power level for the treatment due to the drastic change of the blood perfusion. The reference temperature (T-r) for the controller is based on objective functions to tune its value during the heating process, while a control temperature (T-c) from the thermosensors located in the tumor region is used as the input for the controller. The objective function based on the entire temperature profile is used to evaluate the appropriateness of the heating temperature distribution for a time-variational blood perfusion. Simulation results demonstrate that the tumor region can be rapidly heated to the desired temperature level and maintained at that level despite blood perfusion variation. The resulting temperature profile, the objective function, and the output power level are related to the magnitude of blood perfusion, but are almost independent of the T-c location and the initial setting value of T-r. The fuzzy logic control algorithm with T-r determined from objective functions can be used for controlling the entire temperature distribution through a single control temperature, and the combination of control and optimization allows appropriate temperature fields to be created during the entire heating process. The control algorithm does not require the accurate prior knowledge of the locations of the thermosensors and the appropriate setting value for T-r. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)01805-2].