Divergent Beam Ultrasound Computed Tomography for Differential Thermography

232 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.The applications of divergent beam ultrasound computed tomography for noninvasively estimating temperature change in biological tissue, were examined. This study was prompted by the recognition that both ultrasound speed of propagation and frequency dependent attenuation (two physical properties measurable by ultrasound tomography) are temperature sensitive. Speed generally increases with temperature, and attenuation coefficient generally decreases with temperature, for nonfatty tissue.Compilations of available literature data for thermal dependencies in biological media were created. Polynomial models applied to the available literature data suggested that a linear temperature dependence is a reasonable model over the temperature range of 10 to 40(DEGREES)C for most tissues. The more sophisticated models studied did not provide substantially better results. However, the limited amount of data and the high degree of variability in the data suggested that more study is needed.A study of the variance introduced and propagated by the ultrasound computed tomography data acquisition and image reconstruction showed that the noise introduced by computation was small compared to the noise propagated by the computation. If not for physical difficulties in the available equipment, images of speed and attenuation coefficient could have been reconstructed with a variance of 1 part in 10('3). Temperature changes of 5.5(DEGREES)C could then be estimated with a standard deviation on the order of 0.5(DEGREES)C.Interpolated modeling for algebraic reconstruction was examined, but did not demonstrate itself to be economically justified over conventional algebraic reconstruction.The principal conclusion of this work was that the constraining factor in temperature estimation was the variance in the available literature data. Additional data, with better variance, are required.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD