Design Of Double Mode Hydrogen Fluoride Deformed Birdcage Coil At 7T

The RF coil is one of the most critical components of the entire magnetic resonance imaging system,and its performance is directly related to the emission of the RF pulse sequence and the detection of the MR signal.The birdcage coil has become one of the most common MRI coils due to its large imaging area,the axial direction of the coil parallel to the axial direction of the magnet,and the uniform excitation of the RF magnetic field.The conventional bird cage coil is a completely regular cylindrical structure with a central axis symmetry.The symmetry directly affects the excitation polarization of the RF field,the tuning of the resonance frequency point,and the radio frequency uniformity,thereby further affecting the imaging quality.Based on the application requirements of MRI detection such as flattened and irregular biological tissues,some structural asymmetrical birdcage coils have been developed.Deformed birdcage coils are more suitable for non-cylindrical structures for better signal quality.At the same time,the asymmetric structure of the deformed birdcage coil also brings some new features.In this paper,a deformed birdcage coil with a racetrack structure is proposed.Using the two available resonant modes generated by the non-cylindrical symmetry of the structure,a 16 leg high-pass deformed birdcage coil suitable for 7T small animal imager is designed.Based on the principle of resonant birdcage coil,the CST simulation software is used to study the two available modes of the structure,the hydrogen fluoride resonance frequency,the excitation point and the uniformity of the RF field in the two modes.Firstly,based on the theory of conventional bird cage coil,the resonance mode,electromagnetic field distribution and shielding effect of the conventional bird cage coil of 7T MRI small animal imager are studied by the bird cage coil design software and CST simulation software.Secondly,through the structural deformation,the conventional bird cage coil is designed as a flat track structure.By analyzing the electromagnetic field distribution of each resonant mode of the deformed bird cage coil,the resonant frequencies of the two available modes are adjusted to hydrogen and fluorine respectively by adjusting the capacitance.Finally,the paper also studies the effect of the cage legs on the rectangular side on the frequency spacing of the two available resonance points of the coil,and explores the effects of different tuning methods and different grounding positions on the internal magnetic field of the coil.The racetrack shaped birdcage coil provides two available resonant modes that can be used for MRI excitation and detection of different cores,both of which can achieve a more uniform RF excitation field and a larger imaging area.Compared with the traditional inner and outer double-layer hydrofluoric double-tuned bird cage coil and LC circuit hydrofluoric double-tuned bird cage coil,the coil is not only simple in structure,but also suitable for flat samples,and the coil in the long axis direction is closer to the sample.Therefore,the detection core for the long axis direction has higher sensitivity.