Feedback for ultrasound thermotherapy.

Abstract

Invasive and non-invasive methods for obtaining feedback during ultrasound thermotherapy have been developed and are described in this dissertation. These methods provide quantitative feedback during high-intensity focused ultrasound treatments and ultrasound surgery. Such procedures are used for the therapeutic treatment of tumors and for tissue ablation, and are slowly emerging in the clinic. Feedback for treatment control using ultrasound phased arrays and single-element focused transducers as therapeutic applicators has mainly been obtained with invasive fine-wire thermocouple sensor arrays. Difficulties in placing these versatile sensors has presented a major limitation in their value as feedback elements. The novel invasive and non-invasive feedback methods developed address this limitation, and the feedback problem in general. Invasive methods consist of minimally invasive sensor arrays that have been designed, developed, fabricated, and tested. These sensors not only provide temperature feedback, but acoustic feedback as well. Acoustic feedback has opened the door to more effective and sophisticated treatments and treatment control procedures using ultrasound. Non-invasive methods for feedback and treatment control have also been developed and tested. These methods are based on signal processing of the backscattered diagnostic ultrasound pulse interrogating the tissue region being treated. They have been successfully used to detect tissue damage during ultrasound surgery treatments, to non-invasively estimate tissue temperature changes, to non-invasively localize heating fields, and to control a multipoint temperature treatment in real-time. The algorithms, devices, and underlying assumptions enabling these minimally invasive and non-invasive methods for feedback during ultrasound thermotherapies are described. Phantom, in-vitro, and in-vivo experimental results demonstrating their performance and limitations are also shown.