Image-guided noninvasive surgery with ultrasound phased arrays

The current status and the future needs of image-guided ultrasound phased array systems for noninvasive surgery are addressed. Preliminary results from an integrated image-guided therapeutic phased array system for noninvasive surgical applications currently being developed at our laboratory are shown. The therapeutic array utilizes piezo-composite transducer technology and operates (therapeutically) at 1 and 2 MHz. It consists of 64 elements on a spherical shell with a geometric center at 100 mm from its apex. The array was shown to be capable of producing well defined thermal lesions in tissue media at depths from 40 to 60 mm and to scan therapeutic foci up to +/-15 mm from its geometric center. Image guidance is provided by a modified diagnostic ultrasound scanner which, in addition to providing standard B-scan images of the target region, provides real-time images of the temperature rise due to the therapeutic beam. The temperature information is obtained using a correlation based algorithm for echo displacement estimation, which can be directly related to local variation in tissue temperature due to the therapeutic beam. A complete description of the combined imaging/therapy system is given. Furthermore, illustrative examples of noninvasive real-time image-guided tissue ablation, temperature estimation, and temperature control are presented and discussed.