Design And Development Of ¹H/³¹P Double-tuned RF Coil For 9.4 T MRI System

Magnetic Resonance Imaging(MRI)technology has been widely used in scientific research and clinical diagnosis because of its advantages of high resolution and non-ionizing radiation.Among all the nuclei,1H is the most commonly used nucleus for MRI due to its natural abundance and high MR sensitivity in organisms.However,other nuclei are irreplaceable in physiological processes.For example,MRI based on 31P can detect the changes in energy metabolism,cell membrane and tumor cells in vivo.Therefore,31P MRI is important.Compared with proton,31P MRI signal-to-noise ratio is lower because of its MR sensitivity.Imaging sensitivity and resolution have been greatly improved with the development of high-field MRI technology,which makes 31P MRI possible.In addition to sufficient magnetic field strength,another necessary hardware condition for the realization of 31P MRI and MRS is the 1H/31P dual-tuned coil.Among them,1H-based coil can be used for positioning and shimming.Radio-frequency coil can directly affect the signal sensitivity,the signal-to-noise ratio and uniformity of images.The design and development of 1H/31P double-tuned RF coil will also face new challenges due to the relatively high resonant frequency under high field conditions.The main work of this paper is to design targeted RF coils and RF component circuit based on 9.4 T ultra-high field MRI system platform.The first type of RF coil in this paper was a 9.4 T high-pass birdcage body coil with 12-legs for MRI experiment in mice.Firstly,the multi-physics analysis software was used to model and simulate the coil,and the appropriate value of capacitance was obtained to make the RF magnetic field strong and uniformly.Secondly,the coil was made and applied to the 9.4 T MRI system.Proton imaging with high SNR were obtained of pure water model and mouse,which proved the practicability of the coil.The second type of coil in this paper was a 1H/31P dual-tuned RF coil designed for proton MRI and 31P MRS of mouse brain,which was realized by using two surface coils with inherent geometric decoupling structure.The coil was well matched and decoupled at 1H and 31P nuclear frequencies.The results of proton MRI and 31P MRS in mouse brain obtained by using the constructed coil at 9.4 T were presented in this paper,which proved the feasibility of the coil under ultra-high field.This coil has laid a foundation for the research of double-tuned RF coils of other heteronuclear and has certain reference value.The 1H/31P double-tuned RF coil was made of surface coil structure.In the future,birdcage coil and TEM coil can be used as RF transmitting coil to obtain more uniform RF excitation magnetic field,and the surface coil designed in this paper can be used as RF receiving coil.In order to improve the imaging sensitivity and signal-to-noise ratio,the surface coil can be replaced by the array coil.