Method And Realization Of Digital Magnetic Resonance Transmit/Receive Phase Coherence

In magnetic resonance(MR)experiments,maintaining phase coherence between transmitter and receiver is critical for obtaining accurate phase information from MR signals for correct phase encoding and signal accumulation.Traditional MR instruments use the same analog frequency source to generate RF pulses and quadrature detector local oscillation signals,enabling to maintain phase coherence.In digitalized MR instruments,the transmitter and receiver frequency sources are designed using the direct digital synthesis(DDS)technique,making it more difficult to maintain phase coherence between the transmitter and receiver while improving performance and lowering costs.In this article,we propose a method based on dual reference sources to solve the phase coherence problem between transmitter and receiver in digital magnetic resonance instruments without increasing the sequence complexity or requiring additional hardware circuits.To put the method into practice,this research first finished the transmitter’s software program design and programmable digital logic design,enabling it to receive predefined parameters from the computer and generate the required RF pulses under the control of the pulse sequence.Then,transmitter and receiver reference sources were designed in the field programmable gate array(FPGA),respectively,using the DDS technique.two reference sources use the same system clock with the same resolution,frequency,and output phase in real-time.Finally,the FPGA logic was designed to control the transmitter and receiver to accomplish phase reloading based on the current phase of the reference source when switching frequencies in order to synchronize with the respective reference sources.Because the transmitter and the receiver reference sources are always synchronized during the execution of the pulse sequence,this method can achieve phase coherence between the transmitter and receiver.After testing the transmitter and receiver’s basic functions and phase-coherent functions separately,they were integrated into the laboratory’s MR console to conduct comprehensive performance tests,including loopback tests and spin-echo experimental tests,and the experimental results were further analyzed in this paper to verify the method’s validity.The experimental results show that this method can keep the phase difference jitter between transmitter and receiver within 0.091?,and can be applied to MRI experiments to obtain good image quality,In addition,the method is practical as it does not require additional hardware circuitry or increase the complexity of the pulse sequence.