Design And Implementation Of Key Technology Of Digital Spectrometer Based On PXIe Architecture

Commercial Magnetic Resonance Imaging(MRI)equipment was invented in the1980 s.It has been widely used in clinical diagnosis and life science research due to its advantages such as high soft tissue contrast,arbitrary direction tomography,and no ionizing radiation.MRI system is mainly composed of the main computer,spectrometer,amplifier,main magnet,coil,etc.The spectrometer is the core part of MRI system,which is responsible for sequence operation,signal generation and reception,etc.Its performance affects the imaging quality of MRI equipment.In this paper,based on the original research of our research group,the key technologies of the MRI spectrometer system are deeply studied.Based on the hardware architecture of PXI Express(PXIe)system(including PXIe case,PXIe controller,three NI Flex RIO modules,synchronization and timing module),and the matching software programming environment Lab VIEW programming language to optimize and improve the previous spectrometer system of the research group,and carry out a new structural design.The new spectrometer system can support 1.5T/3.0T MRI system,expansion of transmit and receive channel and parsing of graphically edited sequences,and can be extended to over 7T ultrahigh field.It has the characteristics of short development cycle,convenient system upgrade and excellent performance.Herein,a single module test and an integrated imaging test on a 1.5T MRI system were carried out to obtain expectant imaging results,confirming that the spectrometer design is feasible and effective.The main work of this paper is as follows:1)Propose solutions and optimization schemes for the problems existing in the digital spectrometer system of the previous research group.The design of the sequence generator solves the problems of long scanning start time,limited sequence type and length of the previous spectrometer system.Optimize the design of scanning controller and add sequence analysis,encapsulation protocol and transmission protocol to improve the efficiency of the system operation.Using the performance advantage of PXIe synchronization and timing module,module synchronization and cycle synchronization functions are added to improve the system accuracy and ensure the phase coherence between transmitting and receiving.2)Complete the structural design and function realization of radio frequency(RF)transmitting module and RF receiving module.The main function of RF transmitting module is to generate RF transmitting gating and RF pulse,and to modulate the RF pulse.In addition,as the master control module,it generates synchronous trigger signals and controls the synchronous operation of the lower computer.The RF receiving module generates receiving gating and processes the input magnetic resonance signals such as analog-to-digital conversion,demodulation and subsampling,and currently supports four channels receiving.Each channel adopts an independent signal processing unit.3)Complete the structural design and functional realization of the gradient generating module.The gradient generating module generates three logical gradient waveforms according to the time sequence,and completes the functions of gradient correction,rotation transformation,pre-weighting compensation and so on.