Development of a Fully Digital and Low-frequency NMR System for Polarization Measurement of Hyperpolarized Gases

Abstract

We describe the development of a computer-based and low field NMR spectrometer for polarization monitoring of hyperpolarized gases. The proposed system design replaces as much analog electronics as possible by software and digital electronics. Except for the power amplifier and the preamplifier, the whole system is digital using commercial PC boards. The transmitter is based on the use of a Direct Digital Synthesizer (DDS). Received NMR signals are directly digitalized by the mean of 8-bits analog-to-digital converter (ADC) clocked at 100 MHz. Decimation is preformed to dramatically improve the ADC resolution so as the final achieved resolution can be as high as 14-bits at 5 MHz sampling frequency. NMR signals are then digitally down-converted (DDC). Low pass decimation filtering is applied on base-band signals (I/Q) to enhance much more the dynamic range. The designed system requires little hardware. The transmitter and the receiver are controlled using LABVIEW environment. First NMR signals of hyperpolarized 129Xe obtained with this system are shown. Since this new design allows a high degree of flexibility and ease-of-use, it can be dedicated for others applications.