Design Of Magnetic Resonance RF Coil In Super High Field

Compared with low magnetic field and medium magnetic field,the ultra-high-field magnetic resonance imaging(MRI)has higher imaging speed,signal to noise ratio(SNR)and resolution,which is the popular trend of magnetic resonance frontier research.Compared with low magnetic field and medium magnetic field,the research of RF coils on ultra-high field is still in the phase of exploration.As the higher Larmor frequency in ultra-high field and the shorter wavelength,the destructive interference occurs in image target which seriously affects the imaging quality.Traditional birdcage coils,toroidal coils and saddle coils cannot achieve good imaging results in ultra-high field environments.In order to solve this problem,this project will use the antenna design theory to design a radio frequency coil suitable for ultra-high field 7T.Because the microstrip Yagi antenna has the advantages of simple structure and good directionality,this project proposes to use the microstrip Yagi antenna as a preliminary model of the RF coil,and on this basis,by using two reflector to control the radiation of the RF coil to achieve the purpose of imaging the human body.Then the design of the RF coil element on 7T is designed by simulation optimization.In order to expand the magnetic resonance imaging area and explore the feasibility of whole body imaging,this thesis designs three types of coil arrays using designed RF coil element: planar RF coil array,hexagonal-prism coil array,octagonal-prism coil array,and through HFSS simulation experiments explore the advantages and disadvantages of the three coil arrays.Through the comprehensive analysis and comparison of the magnetic field strength and uniformity of the RF coil array,the coupling between the coils,and the imaging range,etc.,the octagonal prism array is better suits the ultra-high field magnetic resonance imaging due to its more uniform magnetic field distribution and geometrical symmetry on the sagittal and coronal plane.Due to the difference in the dielectric properties of human tissue and the radiant energy of the RF coil is more easily absorbed by the human body in the ultra-high field,which causes local thermal damage.This project used HFSS simulation software to design a human equivalent electromagnetic model.A method combining the human electromagnetic model and the octagonal-prism RF coil array simulation was applied in this study,by analyzing the magnetic field distribution and SAR distribution in human tissue validated the safty of RF coil array.The imaging range of the microstrip Yagi antenna coil array designed in this project covers the human body trunk part and the magnetic field distribution in the region of interest is relatively uniform,which indicated that the coil array has broad a very application prospect in 7T main magnetic field imaging.