The Development Of Low-field MRI Device For Lung Which Is Based On Hyperpolarized ~3He

MRI has been widely recognized due to its multi-parameter,non-radiation,dynamic,continuous observation of tissue physiology and pathological changes.However,the lung as the gas exchange organs,it has rare water content,and the hydrogen proton density is only one tenth of other tissues.Traditional magnetic resonance technology is powerless for lung imaging(black holes).How to introduce MRI technology into lung imaging diagnosis has become a topic that many scientists have been exploring for many years.In order to make up for the lack of water in the lung,we introduced the inert gas 3He as a contrast agent.Firstly,polarize 3He by spin-exchange optical pumping(SEOP)technology,then inhaled the polarized 3He gas into the lungs for examination,which can overcome the difficulty of lung imaging by traditional magnetic resonance technology.Since the polarization is independent of the strength of the magnetic field,not only the spatial information of lung structure but also the functional information of the lung can be obtained in the low field.At present,it has unique advantages in functional imaging of the lung.Based on the work of hyperpolarized 3He gas human lung imaging,this paper developed a special ultra-low field open magnetic resonance system for human lungs.The details are as follows:Based on the built 3He polarization device platform,Based on the established 3He polarization device platform,the transition of the 3He gas to the human lung experiment was completed,and the devices involved in the work were improved and improved,including the main branch of the open polarized cavity.Design and production,design and fabrication of vacuum pumping lines,design and fabrication of polarized 3He gas extraction unit and design of portable storage and recycling equipment for polarized 3He gas.In order to implement hyperpolarized 3He gas lung magnetic resonance imaging,a set of magnetic resonance system especially for ultra-low field lung imaging has been designed and developed.The system consists of four parts: main magnet part,gradient part,radio frequency part and software part:(1)The main magnet part was designed according to the magnetic circuit theorem and electromagnetic field theory method,and the double-plane open permanent magnet type structure was designed to obtain the 600 GS static magnetic field.(2)The longitudinal and transverse gradient coils were designed separately using the target field method to obtain the gradient fields in the x,y and z directions.(3)As the signal hub of the magnetic resonance system,the radio frequency part was divided into the transmitting portion of the transmitted signal and the receiving portion of the received signal.For the first time,a multi-channel 1H/3He double-nuclear quadrature transmit coil array was designed and simulated by using the novel EM field and RF circuit co-simulation method(hereinafter referred to as field-circuit simulation method).In theory,the structure was optimized by the combination of Biot-Savar's law and particle swarm optimization algorithm.Considering the position of lung in human body and getting high signal-to-noise ratio as far as possible,the receiving coil adopted a multi-channel surface coil structure to realize the acquisition of magnetic resonance signals.(4)In the software part,according to the characteristics of fast imaging in hyperpolarized 3He gas lung imaging,fast Flash sequence was selected to complete the acquisition and reconstruction of lung image in tens of seconds.At the same time,several methods which are most suitable for lung imaging are discussed.At present,the verification of the performance parameters of each part has been completed by electromagnetic simulation software and measuring instruments.