A Study Of Focused Sound Field In Layered Biological Media

In recent years, the high intensity focused ultrasound (HIFU) which is used for non-contacting treating tumor gets hold of more and more attention. The mechanism of HIFU sonication is that temperature rising, caused by sound energy transformation to thermal energy in focused region, results in focus tissue necrotizing or disrupting. During clinical therapy, both tissue conformation and sound intensity have influences on the site and shape of HIFU sound field in the multi-layer biological tissue. In order to locate sound field exactlyand treat focus effectively, the HIFU sound field in layer biological media has been studied.The "KZK" equation, which takes into account the sound absorption, diffraction, nonlinearity and media boundary, was adopted to describe focused ultrasonic wave in layer media in this paper. A time domain numerical solution to the "KZK" equation was used to calculate HIFU sound field of a concave spherical ultrasound transducer in different initial conditions. The variation laws of HIFU sound field and sound focal region in the water-fat-liver layer media, which was used to simulate sound propagation of HIFU sonication were analyzed. Then, some experiments were carried out to validate the numerical simulating results. The pressure distributions of sound axial plane were measured in the layered water-agar pattern-water media and water-agar pattern-castor oil media in different sound pressure conditions. Good agreements with simulation show the availability of theoretical analysis.Both theoretical analyses and experimental results show that absorption of layered media and nonlinearity of high intensity sound pressure have influences on the HIFU sound focal regions. Our research results can explain the damage phenomena in related literatures perfectly. It provides a reference basis for analyzing the relation between sound focal region and lesion of tissue in HIFU sonication.