A New Method and Circuit of Ringing Suppression for Low-field NMR Instruments

doi:10.11938/cjmr20223002

Abstract

Abstract:

Accelerating the release of the antenna residual energy to weaken the antenna ringing signal is beneficial to shorten the echo time (TE) of low-field nuclear magnetic resonance (NMR) instruments, thus improving the measurement resolution and signal-to-noise ratio (SNR) of fast relaxation components. The antenna Q value has an opposite effect on the energy emission efficiency and discharge speed. For this reason, we first designed a new Q-switch circuit, which can greatly shorten the energy discharge time while ensuring the transmission efficiency. On this basis, an optimized pulse sequence was applied to overcome the defect that traditional phase alternated pair stacking (PAPs) cannot eliminate 90° pulse ringing, and the SNR was further improved by the method of phase cycling. Finally, the new Q-switch circuit was tested on a 2 MHz core analyzer, the Q value of the antenna was reduced to about 1/5 of the transmit period, and the antenna recovery time was reduced from 280.0 μs to 18.2 μs. Moreover, with the new Q-switch circuit and optimized pulse sequence, the T₂ signal of the fast relaxation component can be effectively obtained when TE=60 μs.

Key words: low-field nuclear magnetic resonance (low-field NMR), Q-switch, ring, signal-to-noise ratio (SNR), pulse sequence

CLC Number:

O482.53

SHI Guanghui,XIAO Lizhi,LIAO Guangzhi,LUO Sihui,HOU Xueli,LU Yapu. A New Method and Circuit of Ringing Suppression for Low-field NMR Instruments[J]. Chinese Journal of Magnetic Resonance, 2023, 40(1): 68-78.

Figures/Tables 12

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Table 1

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	无Q转换器			有Q转换器
	TE=500 μs	TE=100 μs	TE=60 μs	TE=500 μs	TE=100 μs	TE=60 μs
信号幅度平均值(n=5)/μV	11.6	11.3	12.9	11.1	11.2	11.8
信号幅度标准差	1.3	2.0	2.5	0.8	0.9	0.9
信噪比	10.9	1.3	0.3	96.2	91.6	88.5
天线恢复时间/μs	280.0	280.0	280.0	18.2	18.2	18.2