Numerical Simulation Of Magnetic Induction Hyperthermia In Rats

In recent years,Magnetic Induction Thermotherapy(MIH)has been rapidly developed as a new treatment method for tumors,which is called "green" cancer treatment because of its high targeting and low damage to human body.The research in this field is mainly focused on the development of MIH devices and animal experiments,but there are few studies on the multiphysics field coupling calculation and simulation of MIH.In this study,we performed coil modeling and physical field calculation in COMSOL software,analyzed the distribution of electromagnetic and temperature fields of rats in different coil conditions,and investigated the factors affecting MIH,and the results of the study can provide reference for coil design and clinical trials in MIH.(1)The heat generation mechanism of magnetic media and the coupling mechanism of electromagnetic and thermal fields were analyzed.Due to the different sizes of magnetic media,their heat generation mechanisms are mainly divided into eddy current loss,hysteresis loss and relaxation loss,among which the relaxation loss of magnetic fluid nanoparticles has a higher heat generation efficiency.Based on the laws of thermodynamics,the heat generation power of magnetic fluid in alternating magnetic field is derived by using the relaxation loss in magnetic fluid nanoparticles,and the Pennes’ biological tissue heat transfer equation is used as the basic equation for calculating the temperature field distribution and deriving its boundary conditions.The multi-physical field coupling is introduced,and coupling modes can be divided into strong coupling and weak coupling,different coupling modes can be used for different calculation methods,and the coupling mechanism of electromagnetic field and thermal field is clarified as weak coupling.Meanwhile,a rat model and a tumor model are established using modeling software as the basis of the study.(2)The Helmholtz coil was used as the generator of the alternating magnetic field in MIH,and the coil was designed and analyzed for MIH.The rat model was placed in the designed Helmholtz coil and numerical simulations were performed in COMSOL software.The results of the electromagnetic field distribution showed that the magnetic induction intensity of the center of the brain tissue was 10223 A/m,which met the demand of MIH;the maximum electric field intensity of the rat brain tissue was 169.96 V/m,the minimum electric field intensity of the brain tissue was 30.663 V/m,and the electric field intensity of the center of the brain tissue was 94.374 V/m;in the temperature field,the temperature of the center of the tumor could reach46.625 ℃,and the effective treatment temperature line 42 ℃ basically overlaps with the tumor edge,indicating that the tumor tissue can basically reach the treatment temperature.The factors affecting the distribution of electromagnetic field and temperature field were also investigated,including the number of turns,current,radius and spacing,magnetic field frequency and magnetic field strength,and it was found that the number of turns and current had the same effect on the distribution of electromagnetic field,and the magnetic field strength increased from 6134 A/m to 14313 A/m when the number of turns increased from 126 to 294 or the current increased from 6 A to 14 A.The radius and spacing could affect both the uniformity of magnetic field distribution and the peak magnetic induction strength.The magnetic field frequency affects the electrical conductivity and relative permittivity of biological tissues,and in the temperature field,the higher the magnetic field frequency and magnetic field strength,the higher the achievable treatment temperature,and the temperature at the center point of the tumor can reach 51.191 ℃ when the magnetic field strength is 14313 A/m.(3)A solenoid coil was used as the generator of alternating magnetic field in MIH,and the coil was designed and analyzed for MIH,the model was treated in the same way as the Helmholtz coil.The results showed that the magnetic induction intensity in the center of the rat model under the action of the solenoid coil could reach 11.586 m T,and the central electric field intensity could reach 85.056 V/m.Compared with the Helmholtz coil,the magnetic field distribution was more uniform but the peak magnetic induction intensity was reduced;in the temperature field,the temperature in the center of the tumor could reach 45.442 ℃,and from the center of the tumor to the outside,the temperature gradually decreased,so the effective treatment range was slightly smaller than that of the designed Helmholtz coil.The effects of coil turns,current,length,radius,magnetic field frequency and magnetic field strength on the electromagnetic and temperature field distributions were also explored,and the trend was basically the same as that of the Helmholtz coil,with the tumor center temperature changing from 41.118 ℃ to 49.568 ℃ when the magnetic field frequency of the solenoid coil was increased from 60 k Hz to 140 k Hz.It is noteworthy that the changes of solenoid coil length and radius parameters have an effect on both the homogeneity of the magnetic field and the peak magnitude of the magnetic induction intensity,and the effect of the length parameter is more obvious.