| Summary: | My thesis is composed of two parts. Ultrasound hyperthermia is emphasised in part i, and surgical removal of tissues by ultrasonic surgical aspirator is emphasized in part ii. A hyperthermia system making use of overlapping five divergent ultrasonic beams has been developed in my studies. The system is microcomputer controlled. Tissue temperatures are monitored every 30 seconds during treatment with thermocouple arrays, and then the computer adjusts the hyperthermia applicator's output to reach and maintain the therapeutic temperature level in the treated volume. One of the features of the hyperthermia applicator design is that not only divergent field pattern is produced by individual transducer, but also ultrasonic beams are pointed to a focal region by the geometry of the applicator. Computer simulations of the field patterns generated by the applicator in nonabsorbing water medium and simulations of temperature distributions in soft tissue model have been done. Both direct visualization of field patterns in ink-water medium by using Sarvazyan method and measurements with thermocouple probe scanning across and along the field in water are consistent with the computer simulations. In-vitro experiments with pieces of meat and computer simulations of temperature distributions show that the hyperthermia system may be useful in cancer therapy. In-vitro experiments have demonstrated that a large volume of tissue at a few centimetres below the surface can be heat up. Animal experiments have also been carried out and the results are described. Effective blood flows and ultrasonic intensity distributions in the treated region have been estimated by using simplified bio-heat transfer equation. Thermal doses to tissue in treatments are also estimated. In addition, adverse effects of ultrasound on normal blood vessel walls are discussed, and the results of scanning electron microscopy of blood vessel walls are presented. In part ii a theoretical model for tissue fragmentation with ultrasonic surgical aspirator has been suggested. The number of cycles of vibrations required for the CUSA to fragment ox-liver is estimated. The calculated value is consistent with the experimental finding in the order of magnitude. A motor-driven vibrator/ aspirator has been developed in my studies. Its rate of removing ox-liver is comparable to that of the CUSA. Advantages and disadvantages of these two probes are discussed.
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