Thesis (Ph.D.) -- University of Adelaide, Dept. of Microbiology, 1977.

Thesis (M.Sc.) -- University of Adelaide, Dept. of Microbiology, 1979.

The objective of this project is to contribute to the development of therapeutic ultrasound as a surgical technique for the "non-invasive" treatment of discrete liver tumours. The design, focusing and calibration of high intensity sound sources is discussed, and equipment used to treat specimens ranging in weight from a few grams up to several hundred kilograms, is described. The dependence of damage (lesion) dimensions in excised liver samples (at an ambient temperature of 37°C) on the ultrasonic free-field spatial peak intensity (between 1350 and 5400 Wcm 2) and the depth of the focal plane beneath the tissue surface (between 10 and 30 mm) was investigated over a range of exposure times (1<t<40 seconds). Thus, the reproducibility and predictability of the position, shape and size of ultrasonically induced lesions could be assessed. In addition, a simple theoretical model of thermally induced ultrasound damage was developed to predict the effects of ultrasonic parameters and tissue properties, such as thermal diffusivity and blood perfusion, on lesion diameter. The validity of the model was tested extensively, in unperfused porcine liver. Other experiments were performed in vivo to investigate both a host's response to ultrasonic liver damage, and the feasibility of placing lesions side by side (in arrays), in an attempt to destroy all the cells within a volume much larger than the focal region. After preliminary studies in excised tissue, both normal and tumour bearing livers were exposed. The clear visual and histological differences between treated and normal liver parenchyma, and between tumour cells before and after treatment are also reported. The possibility of imaging ultrasound lesions was investigated in excised liver using diagnostic ultrasound, and in vivo by obtaining magnetic resonance images of both liver and tumour, before and, at various times up to 8 weeks, after ultrasound exposure. Finally, the potential to produce localized ultrasound damage non-invasive1y in vivo, using pulse-echo ultrasound imaging to plan a treatment, was explored, and although extensive dosimetric studies are required before liver tumours can be treated clinically, much of the necessary physics of this high intensity focused ultrasound technique has been completed.

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