Study And Optimum Design On Multi-element Focused Ultrasound Lens

High intensity focused ultrasound technique is a promising technique for non-invasive treatment of solid, deep-seated tumors. The most pivotal technique is focalizing technique in HIFU technique. At present, self-focused,ultrasound phased array,acoustic lens and so on are in common use. The focused system which is combined by transducer and multi-element focused lens, combines the excellences of ultrasound phased array focuced and munti-elenment transducer focused. It's effective and applied. In this paper, the lens are taken as a phase modulator, and the acoustic field of a single-element conical lens,a single-element paraboloid lens,two multi-element conical lens,two multi-element paraboloid lens with different shape parameters are simulative calculated by means of Rayleigh-Sommerfeld Integral. The axial,radial sound intensity distribution and the sound beam profile(-3dB) diagram are given. The parameters which describe the focused lens'acoustic field are calculated and primary chosen which have good focused effect.The Pennes bio-heat transfer equation are calculated by applying the finite difference methord, the tissue's temperature changes in the focused area are simulative calculated. Taken tissue's temperature raising up to 23℃as a threshold , the best optimum shape parameters of the lens systems are determined to get a large and high focused area, and shorter treatment time. The numerical calculational results shows that when having a same aperture, the single-element lens are fit to curing the deep-seated tissue which have big focus,deep focused depth and big focused area; the multi-element lens are more fit to the low-seated , bigger therapy area which have small focus,low focused depth and much bigger radial heating area than the single ones; the conical lens has smaller focus,low focused depth but bigger radial heating area than the paraboloid lens.