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Title page for ETD etd-04082016-131931


Type of Document Master's Thesis
Author Hasselwander, Christopher Jordan
Author's Email Address chrishasselwander@gmail.com
URN etd-04082016-131931
Title gr-MRI: A Software Package for Magnetic Resonance Imaging Using Software Defined Radios
Degree Master of Science
Department Biomedical Engineering
Advisory Committee
Advisor Name Title
William A. Grissom, Ph.D. Committee Chair
Brett C. Byram, Ph.D. Committee Member
Mark Does, Ph.D. Committee Member
Keywords
  • spectrometer
  • pulse sequence
  • MR
  • NMR
  • software
  • hardware
  • radio
  • home-built
Date of Defense 2016-04-08
Availability unrestricted
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.

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