Design And Research Of Low Current Magnetic Field Measurement System For MRI Superconducting Magnet Coil

With the popularization of MRI(Magnetic Resonance Imaging),MRI market has higher requirements for manufacturers.As one of the important indicators of MRI,the imaging quality has been widely concerned.Superconducting magnet is the main component to provide magnetic field for MRI.There are two key indices:main magnetic field strength and field homogeneity of DSV(Diameter of Spherical Volume).Actually,the field homogeneity in DSV is much more difficult to be controlled than main magnetic field strength,because it is related to the dimensional accuracy of assembly and various matching errors.It is rarely found that the main magnetic field strength is not meet to standard in the production,but the homogeneity is out of range sometimes.The repair and time cost caused by DSV homogeneity adjustment are the pain points of MRI manufacturers at present,so a measurement system that can check DSV homogeneity in advance is needed.The low current magnetic field measurement system designed in this paper can measure and analyze magnetic field homogeneity of superconducting magnet coil at room temperature in advance.In this way,the homogeneity of magnetic field can be screened before superconducting magnet coil being assembled into liquid helium tank,so as to improve productivity and reduce cost.The design process is divided into hardware design and software development.The DSV of MRI is a sphere with diameter of 40-50 cm and has high uniform static magnetic field.The measurement method is from physical principle of DSV,and the hardware selection and design are based on the measurement method.After simulation analysis for magnetic field of DSV,the measurement and analysis parameters of the system can be defined,basing on the relationship between superconducting magnet coil and homogeneity of DSV magnetic field.The software is designed based on measurement parameters and hardware control requirements.The hardware part mainly meets the spherical motion of the sensor and provides power drive.The software part mainly includes hardware control,data acquisition and analysis.In order to ensure the accuracy of measurement after system established,the error source analysis is carried out,and measurement method is optimized to eliminate some errors.Finally,the uncertainty evaluation of the whole system is carried out,so that the reliability of the whole system can be directly represented by the relative uncertainty and expanded uncertainty.