Finite Element Analysis On The Three Dimensional Temperature Fiele Of Femur Tumor In The Process Of Hyperthermia And The Thermal Stress Of Hip Prosthesis

In hyperthermia processing,because of the complexity of the human body tissue and the temperature measurement method existing limitations.To be precise,fast and comprehensive get the temperature distribution of cancer and the surrounding tissues is full of difficulties.In this paper,we will use the medical image processing software and finite element method to study the three dimensional temperature field of hyperthermia. In the condition of accurately established three dimensional model of the femoral with medical image processing software MIMICS, according to the relation between the HU and material properties by MIMICS provided,give the femur kinds of materials,make its geometric shape and physical attributes close to thehuman physiology femoral.Then taking the heat transfer and Pennes biological heat transfer equation for theory,set the thermal physical parameters of bone tissue,given the initial and boundary conditions,using the finite element analysis software ANSYS simulation hyperthermia processing,obtained the three dimensional temperature distribution law of femoral by heat treatment.The results show that femoral organization has good hinder effec to theat transfer;In the sagittal plane,The closer from the heat source center,the more temperature isoline dense,the greater temperature gradient,and temperature isoline into the oval;In coronary plane,temperature isoline similar circle,the farther away from the heat source,the more temperature isoline sparse,the smaller temperature gradient;In cross section,temperature isoline to heat source as the center into elliptic distribution,from inside to outside temperature gradually reduced.Femoral temperature curve in the three dimensional space into ellipsoid distribution with heat source as the center,the closer from heat source, the greater the temperature gradient;Because of the three dimensional temperature space distribution of femoral is asymmetry when hyperthermia,The necessary method is using more than a heat source to guarantee temperature field and tumor tissue " shape similar " matching.Analysis results have important meaning to determined the number of needle and location and heating strength.When the femur tumor tissue spread to the large size or other factors cause body physiology hip function failure serious,must be adopted to hip replacement.Hip replacement now is very mature,but is still inadequate,often need of revision surgery.Research shows that inappropriate prosthesis material choice would lead to the failure rate increases.For the selection of materials, consider its thermal characteristics lead to surgical failures rare reports.In this paper,we analysis the stress distribution of prosthesis when the hip joint has been replaced without heating and in consideration of the thermal effect by finite element method,Assumes that prosthesis,bone cement and femur are linear elastic and isotropic materials which construct a concentric cylinder,in CAD software establishment hip replacement model,Import ANSYS analysis software and give materials to prosthesis,bone cement and femoral,mesh,set boundaries and initial conditions,with basis of the heat transfer and thermo elasticity,using thermal analysis-stress analysis coupling function of ANSYS software,obtained the axial stress of prosthesis,bone cement,femur and the interface shear stress along axial of the prosthesis/bone cement and bone cement/femur when the prosthesis are made of titanium alloy and cobaltchromium alloy are acquired separately by mechanical analysis and FEM simulation.The results indicate that the interface failure is the primary failure mode of the femur-prosthesis system.With the existence of thermal effect,the form of shear failure which is mixed rather than pure generates on interface,in addition,this case accelerates the interface failure of femur-prosthesis system and the loose of prosthesis stem.The possibility of interface failure which result in operation failure will ascend when the cobalt-chromium alloy is used,because the thermal expansion coefficient is higher in cobalt-chromium alloys than titanium alloy.Therefore,the choice of the prosthesis with low expansion coefficient can decrease the possibility of the interface failure to increase the success ratio.