Numerical Simulation Of Temperature Field In Focal Region Formed By High Intensity Focused Ultrasound

Objective:High Intensity Focused Ultrasound(HIFU)tumor therapy is a promising technique that uses high intensity ultrasound to destroy tissues in a confined region which will avoid traditional invasive methods.It features the application of HIFU, high local temperatures of above 60℃and short treating time of a few seconds.It has been widely used due to its effective,micro-impassivity and deep into human tissues' advantages.Application of this technique may spare patients from ionizing radiation, chemical reactions and poison-minus effect.But it is difficult for existing HIFU tumor therapy system to monitor the focal region temperature in real-time accurately and objectively and predict the shape and size of the focal region.So complications such as skin burn,damage of overlying tissues and residual of target tumor may occur.In order to avoid these clinical complications,it is very necessary to investigate the focal region temperature in human tissues and predict different factors that effect on HIFU temperature field.Methods:In this work,FDTD method which was proposed by Nagayoshi Morita to simulate pressure,velocity of nonlinear propagation high intensity ultrasound, together with Pennes bio-heat transfer equation are applied to simulate temperature field in a 3-D cylinder coordinate which is established referring to human brests, temperature distribution of different propagation time is simulated.Result:The simulation results display that the temperature of focal region is in human tissues increase when heating time becomes longer.Then,it keeps invariab in a short time.The focal length produced by HIFU propagation is different with HIFU geometric focal length.The temperature distribution are the same in skin and slight fat with different excitation function,but different in focal area.Different choice of ultrsound dosage will lead to the changes of temperature field.Blood perfusion has an important influence on HIFU temperature field.Conclusion:This work simulate temperature field in HIFU.3-D cylinder coordinate is established referring to human brests and FDTD method is used to calculate temperature field numerically.The conclusion are as follow:(1)add integrated layer or not will take little influence on the distribution of HIFU temperature field.But without the integrated layer,the central temperature of focal region will be higher.(2)With the same ultrasound power densities and exposure time,When the frequency becomes higher,the skin temperature on the center becomes higher than slight fat,the area of focal region decreases,the focal length shortens,and a slightly increased skin temperature on the center is observed.(3)As the frequency and exposure time are the same,when ultrasound power densities becomes higher,the area of focal region increases but the focal length does not change very much.The temperature of skin increased dramatically due to higher ultrasound power densities.(4)With the same frequency and ultrasound power densities,when exposure time becomes higher,the area of focal region increases but the focal length does not change very much.The temperature of skin increased.(5)When the Ultrasound dosage are same,the area of focal region and focal lenth will decrease but central temperature will be higher with blood perfusion.