| Summary: | 博士 === 國立臺灣大學 === 電機工程學研究所 === 91 === The purpose of this paper is to investigate the feasibility of conformal heating for external ultrasound hyperthermia by using a phased array transducer with mechanical motion. In this system, a one-dimensional phased array is arranged on a shaft and it is moved along the shaft, while dynamically focusing on the planning target volume (PTV) with numerous of focal spots. To prevent the overheating in the intervening tissue between the skin and the PTV, the shaft and the phased array are rotated together to enlarge the acoustical window. For the purpose of conformal heating, the power deposition of the PTV is constructed by the combinations of the focal spots, and an iterative gradient decent method is then used to determine the optimal set of power weightings of the focal spots. Different shapes of tumors were evaluated, and the simulation results demonstrate that the volume percentage of the PTV with temperatures higher than 43oC for the successful heating is over 95%. The overheating volume outside the PTV is less than 25% of the PTV. This method is able to provide good conformal heating for external ultrasound hyperthermia. The concept of combining electrical focusing and mechanical motion has the advantages of both enlarging the acoustic window and providing dynamical focusing ability; that is the essence of successful conformal heating. Furthermore, to improve the transient response of this system, a controller base on a cost function is proposed. By minimizing the cost function, appropriate power weighting set in a control loop can be obtained. This controller is robust with respect to the model error; time-varying perfusion, non-uniform perfused situation, and error predicted blood perfusion cases were test, and no significant effect on the controller’s performance was observed.
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