Thursday, October, 30 1997
A two-dimensional non-invasive temperature-change estimation algorithm based on the analysis of diagnostic backscattered ultrasonic RF-data is presented in this talk. The technique consists of first estimating the echo time-shift map due to the combined effects of thermal dependence of speed of sound and thermal expansion in tissue. The estimated time-shift map is then processed in order to provide an estimate of the two-dimensional temperature map. An experimental system consisting of a therapeutic ultrasound unit and an ultrasound imaging unit was used to demonstrate the capabilities of the proposed method when estimating temperature profiles in phantom and in vitro tissue heating experiments. The system performance is quantitatively characterized in terms of the accuracy, spatial resolution, and ripple present in the temperature estimates. The ripple is shown to be a consequence of the thermo-acoustic lens effect resulting from local changes of the speed of sound in heated regions. A spatial band-limited filter design approach is adopted to control the tradeoff between the desired spatial resolution and the acceptable level of ripple in the temperature estimates. Moreover, possible applications and some limitations of the proposed technique are discussed.
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