A Development Of New Digital Magnetic Resonance Imaging Transmitter Based On PXIe Architecture

Magnetic Resonance Imaging(MRI)is a new imaging method developed and matured in the 20 th century.It is mainly used in medical imaging and some other aspects.It is a kind of atomic nucleus produce signals and then processed by computerized imaging techniques under the excitation of a designed RF pulse in an external uniform magnetic field.The MRI system is mainly composed of a host computer,a spectrometer,a magnet,a power amplifier,a gradient coil,and a radio frequency coil.The Spectrometer is the heart of the magnetic resonance system.It is mainly uesd for generating,transmitting and processing of various hardware signals in the MRI system.The radio frequency transmitter is an important part of the spectrometer.In magnetic resonance imaging system,it is mainly used to emit radio frequency pulses to stimulate the atomic nucleus(usually the hydrogen nucleus)in the patient to obtain the physiological information of a specific part of the patient.This article aims to design a highly integrated,high-performance RF transmitter that can meet the needs of magnetic resonance imaging systems.This article designed and accomplished a new type of digital spectrometer transmitter based on the PXIe architecture,using the National Instruments(NI)fourchannel transceiver adapter module NI-5783 and the Flex RIO FPGA module PXIe-7972 cascade.LabVIEW replaces the traditional FPGA underlying hardware description language VHDL or Verilog for software development,which greatly saves development time and improves development efficiency.The frequency of the RF signal that the spectrometer transmitter designed in this article can transmit signal from DC(0.01Hz)to 200MHz;at a center frequency of 64 MHz or 128 MHz,with a bandwidth of 2MHz,the output spurs are lower than-70dBc;with fast frequency switching and amplitude Switching function: The switching time between 50 MHz and 100 MHz is less than 2 cycles,and the maximum time is less than 40ns;at 64 MHz,the voltage switching time between 0 and 2Vp-p is within 1 cycle(16ns),and Guarantee the rapid switching of amplitude and frequency at the same time;The spectrometer transmitter designed in this paper can output the sinc RF soft pulse designed by the center at 64 MHz and 128 MHz,which proves that this design can be applied to the MRI system with 1.5T and 3T magnetic field intensity.The use of a synchronous reset method enables phase coherence between the transmitter and the receiver to avoid the introduction of artifacts.We designed a new type of digital spectrometer based on the PXIe architecture consisting of a radio frequency transmitter(TX),a radio frequency receiver(RX),a gradient amplifier(GTX),and a scanning controller(SBC),and succeed experiment in the 1.5T magnetic resonance imaging system EchoStar,Alltech Medical Systems Corporation,replace the commercial spectrometer completed,at the control of the GRE sequence,under Single Band and Multi Band imaging technology,performed the water model imaging.In verifying the feasibility of the new digital magnetic resonance imaging spectrometer based on the PXIe architecture.