gr-MRI: A Software Package for Magnetic Resonance Imaging Using Software Defined Radios

Abstract

Purpose: To develop software that enables the rapid implementation of custom MRI spectrometers using commercially-available software defined radios (SDRs). Methods: The gr-MRI software package comprises a set of Python scripts, flowgraphs, and signal generation and recording blocks for GNU Radio, an open-source SDR software package that is widely used in communications research. gr-MRI Implements basic event sequencing functionality, and tools for system calibrations, multi-radio synchronization, and MR signal processing and image reconstruction. It includes four pulse sequences: a single-pulse sequence to record free induction signals, a gradient recalled echo imaging sequence, a spin echo imaging sequence, and a spin echo inversion recovery imaging sequence. The gr-MRI sequences were used to perform phantom imaging scans with a 0.5 Tesla tabletop MRI scanner and two commercially-available SDRs. One SDR was used for RF excitation and reception, and the other for gradient pulse generation. The total SDR hardware cost was approximately $2000. The frequency of radio desynchronization events and the frequency with which the software recovered from those events was also measured, and the SDR’s ability to generate frequency-swept RF waveforms was validated and compared to the scanner’s spectrometer. Results: Gradient echo and spin echo images geometrically matched those acquired using the scanner’s spectrometer, with no unexpected distortions. Inversion recovery images exhibited expected behavior as a function of inversion time. Desynchronization events were more likely to occur at the very beginning of an imaging scan, but were nearly eliminated if the user invokes the sequence for a short period before beginning data recording. The SDR was able to produce a 500 kHz bandwidth frequency-swept pulse with high fidelity, while the scanner’s spectrometer produced a waveform with large frequency spike errors. Conclusion: The developed gr-MRI software can be used to develop high-fidelity, low-cost custom MRI spectrometers using commercially-available SDRs.