High-Speed Data Acquisition System and Receiver Configurations for Time-Domain Radiofrequency Electron Paramagnetic Resonance Spectroscopy and Imaging
✍ Scribed by S. Subramanian; R. Murugesan; N. Devasahayam; J.A. Cook; M. Afeworki; T. Pohida; R.G. Tschudin; J.B. Mitchell; M.C. Krishna
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 347 KB
- Volume
- 137
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
Design strategies, system configuration, and operation of a dualchannel data acquisition system for a radiofrequency (RF) timedomain electron paramagnetic resonance (EPR) spectrometer/imager operating at 300 MHz are described. This system was configured to incorporate high-speed analog-to-digital conversion (ADC) and summation capabilities with both internal and external triggering via GPIB interface. The sampling rate of the ADC is programmable up to a maximum of 1 GS/s when operating in a dual-channel mode or 2 GS/s when the EPR data are collected in a single-channel mode. By using high-speed flash ADCs, a pipelined 8-bit adder, and a 24-bit accumulator, a repetition rate of 230 kHz is realized to sum FIDs of 4096 points. The record length is programmable up to a maximum of 8K points and a large number of FIDs (2 24 ) can be summed without overflow before the data can be transferred to a host computer via GPIB interface for further processing. The data acquisition system can operate in a twochannel (quadrature) receiver mode for the conventional mixing to baseband. For detection using the single-channel mode, the resonance signals around the center frequency of 300 MHz were mixed with a synchronized local oscillator of appropriate frequency leading to an intermediate frequency (IF) which is sampled at a rate of 2 GS/s. Comparison of quadrature-mode and an IF-mode operation for EPR detection is presented by studying the FID signal intensity across a bandwidth of 10 MHz and as a function of transmit RF power. Imaging of large-sized phantoms accommodated in appropriately sized resonators indicates that IF-mode operation can be used to obtain distortion-free images in resonators of size 50 mm diameter and 50 mm length.