MR Experiments Using a Commercially-Available Software-Defined Radio

Purpose: Conventional commercial MR spectrometers are often limited in configurability, portability, scalability and cost. This has led several researchers to build lower-cost, smaller and more customizable architectures in-house [1-6]. One such approach is a software-defined radio (SDR) architecture [7], comprising high-speed A/D and D/A converters, an FPGA to perform high-bandwidth digital mixing and filtering, and a USB or Ethernet link to a PC for real-time data transfer. SDR’s have several strengths, including high-bandwidth direct RF signal synthesis and digitization with high bit depth, high configurability and low cost. In this work we describe NMR and MR imaging experiments using the commercially-available Ettus Research USRP1 SDR (Ettus Research, Santa Clara, CA, USA), which retails for around $700 USD. The work was motivated by the need for a low-cost spectrometer for teaching an MR engineering course, and for a transmitter that could generate adiabatic pulses with large frequency sweeps for Bloch-Siegert shift-based RF encoding experiments on a 0.5 Tesla Oxford Maran scanner (Resonance Instruments, Witney, UK) [8,9].