Labthermics Technologies (United States)

The feasibility of using novel ultrasound phased arrays consisting of array elements larger than a wavelength and randomly located on a spherical shell have been investigated, both theoretically and experimentally, for surgical applications. Random placement of the sources minimizes grating lobes associated with the array. The size of the treatment volume, i.e., the region over which the focus of the array can be electronically scanned, is determined by the directive, overlapping beams from the circular sources that constitute the array elements. The treatment volume and the intensity at the focus have been determined for a range of frequencies and source dimensions. The source size and frequency determine the number of elements that are needed to generate the intensities required for tissue ablation. Gaussian sources were also evaluated for use in such an array. Results are presented for arrays consisting of 64 elements.

Ultrasound phased arrays offer several advantages over single focused transducer technology, enabling electronically programmable synthesis of focal size and shape, as well as position. While phased arrays have been employed for medical diagnostic and therapeutic (hyperthermia) applications, 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 (2-4 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. The present work 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 tissue ablation applications. A hexagonally packed array consisting of 108 8-mm-diameter circular elements mounted on a spherical shell was modeled theoretically and a prototype array was constructed to examine the feasibility of sparse random array configurations for focal surgery. A randomly selected subset of elements of the prototype test array (64 of 108 available channels) was driven at 2.1 MHz with a 64-channel digitally controlled RF drive system. The performance of the prototype array was evaluated by comparing field data obtained from theoretical modeling to that obtained experimentally via hydrophone scanning. The results of that comparison, along with total acoustic power measurements, suggest that the use of sparse random phased arrays for focal surgery is feasible, and that the nature of array packing is an important determinant to observed performance.