High-Speed Data Acquisition System and Receiver Configurations for Time-Domain Radiofrequency Electron Paramagnetic Resonance Spectroscopy and Imaging

• Published in: Journal of magnetic resonance (1997) Vol. 137; no. 2; pp. 379 - 388
• Main Authors: Subramanian, S., Murugesan, R., Devasahayam, N., Cook, J.A., Afeworki, M., Pohida, T., Tschudin, R.G., Mitchell, J.B., Krishna, M.C.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-04-1999
• Subjects: Data Collection; Diagnostic Imaging - instrumentation; Electron Spin Resonance Spectroscopy - instrumentation; Image Processing, Computer-Assisted; Phantoms, Imaging; Sensitivity and Specificity
• DOI: 10.1006/jmre.1998.1697
• EISSN: 1096-0856
• ISSN: 1090-7807

Design strategies, system configuration, and operation of a dual-channel data acquisition system for a radiofrequency (RF) time-domain electron paramagnetic resonance (EPR) spectrometer/imager operating at 300 MHz are described. This system wasconfigured 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 (224) 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 two-channel (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.