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The main objective of this master’s thesis is to investigate the possibility of applying spatially-filtered continuous-wave acoustic tomography to the detection of breast cancer. A continuous acoustic wave is transmitted through the specimen in this tomographic imaging method. Any scattered waves that do not positively contribute to the projection are filtered out using an aperture. There is evidence to suggest that cancerous lesions in the breast have a higher speed of sound than surrounding tissues. This imaging method produces two tomograms of the specimen simultaneously: one showing the internal speed of sound, and the other showing the internal acoustic attenuation coefficient. There is the possibility for a third imaging modality, acoustic dispersion tomography, to be applied to this imaging method. Two proof-of-concept prototype spatially-filtered continuous-wave acoustic tomography scanners were designed and built: one that uses a collimated beam to interrogate the specimen, and another that uses a confocal beam. A least-squares tomographic reconstruction algorithm was chosen to reconstruct the tomograms this method creates. A prostate phantom and a breast phantom were imaged with the confocal tomographic scanner. The tomograms of the prostate phantom show two 1 cm lesions which are consistent with information from the phantom manufacturer. Further work is required to properly validate the speed of sound and acoustic attenuation measurements this method produces. / Graduate

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This thesis presents the development of a computer model for the simulation of the sidescan sonar process. The motivation for the development of this model is the creation of a unique and powerful visualisation tool to improve understanding and interpretation of the sidescan sonar process and the images created by it. Existing models tend to generate graphical or numerical results, but this model produces synthetic sidescan sonar images as the output. This permits the direct visualisation of the influence of individual parameters and features of the sonar process on the sidescan images. The model considers the main deterministic aspects of the underlying physical processes which result in the generation of sidescan sonar images. These include the propagation of the transmitted pulse of acoustic energy through the water column to its subsequent interaction and scattering from the rough seafloor. The directivity and motion characteristics of the sonar transducer are also incorporated. The thesis documents the development of the model to include each of these phenomena and their subsequent effect on the sidescan sonar images. Finally, techniques are presented for the investigation and verification of the synthetic sidescan images produced by the model.

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