This thesis addresses the challenges of measuring the acoustic (sound speed, attenuation, absorption and nonlinearity coefficients), thermal (thermal conductivity) and histological properties of soft tissues that lie within the HIFU beam during treatment. Differences in these tissue properties may affect the delivery of thermal therapies, but may also provide a basis for their monitoring with ultrasound. Novel measurement techniques have been developed and validated for each parameter. Measurements have been made in rat, bovine and human tissues. The finite amplitude insertion substitution (FAIS) method was used to obtain the attenuation coefficient and speed of sound. The absorption coefficients were determined using a thermometric method involving a Fabry-Perot fibre optic sensor. Nonlinearity coefficients were measured using the FAIS method with a large area hydrophone detector. Using these methodologies, a system that allows the measurement of all these parameters in the same region of a sample has been designed and built. Tissue thermal conductivity was determined using two methods: the first used a system designed to provide unidirectional heat flow between a source and heat sink. 35 MHz ultrasound (US) images were used to determine the volume of air trapped in the tissue sample, thus allowing corrections to the thermal conductivity to be made using the standard bio-heat equation model. The second method was a non-invasive method in which HIFU heating was combined with ultrasound thermometry. Finally, a Matlab code which allows quantification of important aspects of Haematoxylin and Eosin (H&E) stained histological images has been developed. This has been used to correlate the histological appearance of samples with their thermal and acoustic properties.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:544149 |
| Date | January 2011 |
| Creators | Retat, Lise |
| Publisher | Institute of Cancer Research (University Of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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