NMR experiment control system with an interval programmable generator

Abstract

Exceptionally high demands on the time control accuracy and the experiment flexibility are imposed by modern nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI). A critical component of NMR equipment is a specialized device responsible for synchronizing and controlling all nodes and devices during the experiment. In this paper, a device control system with interval programmable generator (programmator) of arbitrary pulse sequences implemented on programmable logic integrated circuits (FPGAs) is proposed. The designed system architecture provides simultaneous control of up to 245 external devices in mode both asynchronous and synchronous with the pulse sequence via special instruction words. A universal instruction format used for both internal and external devices provides a simple way to connect any new external device to the control system. The internal instructions set, which includes intervals, nested loops and macros allow to develop and implement the highest complexity pulse sequences in NMR experiments. The duration of the interval set by a single instruction can take values from 20 ns to 0.334 seconds. For any fragments of the pulse sequence, it is possible to form cycles with up to 2¹⁶ repetitions, including nested (cycle within cycle) cycles with a nest depth of 16. Thus, usage a memory for only 2048 instruction words allows to reach the total duration of the generated sequence 10⁸⁰ s (with a 20 ns resolution).