TEMPERATURE AND ACOUSTIC FEEDBACK/THERAPEUTIC ULTRASOUND

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The broad long-term objective of the research in this revised application is to develop completely noninvasive ultrasound-guided phased-array applicator systems for, a range of therapeutic applications, e.g., hyperthermia, rapid-heating hyperthermia, and tissue ablation. Our preliminary research results indicate that noninvasive measurement of changes in tissue temperature is feasible using standard diagnostic ultrasound pulse-echo data and appropriate digital signal processing (DSP) algorithms. We have experimentally verified that changes in tissue temperatures can be estimated accurately and with high spatial resolution by estimating frequency shifts in the spectrum of the RF pulse-echo data at a specified location. Furthermore, noninvasive acoustic feedback for focusing and target (tumor) tracking through tissue inhomogeneities is also feasible. This, however, requires the development of new phased- array applicator systems capable of transmit-receive operation. Transmit- receive capability will give phased-array applicators the ability to self focus in the presence of tissue inhomogeneity in a similar manner to imaging arrays currently used in practice. Self-focusing of therapeutic arrays, while similar in principle to self-focusing of imaging arrays,, does present some new challenges. We intend to develop self-focusing algorithms for optimal therapeutic arrays. Noninvasive measurement of temperature changes and self-focusing capability of therapeutic applicators coupled with guidance using real-time ultrasound imaging systems will undoubtedly provide an attractive system for diathermy and tissue ablation (surgery). The versatility, low cost, and low morbidity associated with noninvasive ultrasonic procedure will have a positive impact on the health care delivery for a significant number of patient groups, e.g., breast cancer, prostate cancer, and liver cancers.