Evolution of high-intensity focusing systems for different applications in medicine (Review)

The evolution of high-intensity focusing systems for application in medicine has been outlined from their introduction (in the 1950s) to date. This work is in fact a review with two sections. The focusing systems for medical application discussed under the first section are based on using single focusing transducers with a radiating element shaped as a section of a spherical shell. Attention is mainly given to the devices developed at the Andreev Acoustics Institute in the 1970s–1980s; focusing systems developed abroad in the past few decades and most widely clinically used are also briefly discussed there. The second section of the review is devoted to focusing systems based on phased arrays which allow users not only to electronically steer the focus within a selected range, but also, especially importantly for various medical applications, to simultaneously create several foci. The main attention under the second section is given to the two-dimensional phased arrays with randomized location of elements on the surface, which the Acoustics Institute developed in active collaboration with others. It has been shown that irregularity in the location of elements either substantially improves the quality of spatial intensity distributions by reducing the level of secondary maxima of intensity in the array-induced fields or allows to considerably reduce the number of elements in the array with the same quality of distributions. The paper discusses principles of designing such arrays, methods of their calculations and possible applications.