A number of studies have suggested that noninvasive surgery using high intensity ultrasound ablation of tissue is feasible, and offers significant advantages over conventional surgical techniques for many applications. Here, a focused ultrasound transducer is used to insolate a small tissue target or targets deep within the body causing immediate ablation of targeted tissue. In the past, ultrasound delivery systems for high intensity focal surgical applications have been single element geometrically focused devices, employing bowl-shaped transducers or lenses to provide the desired focal region. However, ultrasound phased array technology may also be useful for surgical applications, enabling electronically programmable synthesis of focal size and shape, as well as position, thus eliminating the necessity of cumbersome mechanical scanning apparatus. While phased arrays have been employed for medical diagnostic and therapeutic applications (hyperthermia), there remain fundamental problems associated with their use for surgery. These problems stem largely from the small size of each array element dictated by the wavelength employed at surgical application frequencies (approximately 4 MHz), the array aperture size required for the desired focal characteristics, and the number of array elements and electronic drive channels required to provide RF energy to the entire array.This Phase I proposal involves the theoretical and experimental examination of novel ultrasound phased arrays consisting of array elements larger than one wavelength minimizing the number of elements in an aperture through a combination of geometric focusing, directive beams, and sparse random placement of array elements for direct application to tissue ablation applications. The specific aims of the proposed work are to1) examine theoretically the feasibility of sparse random array configurations for focal surgery,2) build a prototype test array to be driven with an existing maximum 64 channel digitally controlled RF drive system for examining the feasibility of such systems for surgical ablation applications, and3) test the performance of the prototype array to verify the energy deposition pattern and overall performance of the new array configuration.Phase II will apply the results obtained in Phase I to the design of a prototype ultrasound ablation system suitable for animal studies to demonstrate the potential of this technology.National Cancer Institute (NCI)
