Investigation of a spherical-section ultrasound phased array for hepatic ablation

A 3D ultrasound thermal model with a 3D finite element representation for modeling the thermal diffusion effects for hepatic ablation induced by spherical-section ultrasound phased array was developed. The model was first validated against available published measured data in rat liver. Using the validated model,effects of blood perfusion and heating schemes on lesion formation were studied for both single focus and split-focus intensity patterns. It was shown that for single focus sonication pattern the short-duration(～2 s) and high-intensity(～1250 W/cm2) heating scheme can completely reduce the cooling effect of the blood perfusion. The lesion shape and size were significantly altered by perfusion for split-focus pattern even with a rapid heating scheme when the focus spacing was larger than 2.4 mm. Underdosed areas might be present between two foci. Prolonging ex-posure time or shortening focus spacing can reduce the cool region between two foci. In addition,the influences of thermal and acoustic parameters were also studied. When the therapy depth is short(<5 cm) ,the lesion size monotonically increases with increasing attenuation coefficient that ranges from 5.4 to 11 Np/(m?MHz) .

A new method for uniform local heating deep in body using ultrasound phased-array system

A new method for targeted heating of deep tissue was developed by using an ultrasound phased-arraysystem which can generate various multiple foci patterns by electronically changing its amplitude or phasepattern.This method involves using a technique of combining switching and rotating of multiple foci pat-terns to create a uniform temperature over tissue volumes in various size.Using this method,the targettissue deep in the body can be heated to a specified temperature,which gives conditions for thermo-sensi-tire liposomes release.A simulation study for a 108-element,spherically sectioned array was performed todetermine an optimal heating scheme from a set of multiple focus fields which were produced by inputtingdifferent combinations of phases and amplitudes.Comparisons of a static multiple foci field,the switchedfields and the switched-rotated fields indicated that the technique of combining switching and rotating ofmultiple foci patterns has advantages of both lowering the peak temperature and evening the temperaturedistribution.The simulation results also show that the therapeutic heating zones in various size(φ5mm～φ40mm)with uniform temperature distributions can be obtained employing the combined method.Theseresults offer significant data for designing thermotherapy equipment for tumor-specific drug release withthermo-sensitive hposomes.