Phosphorus magnetic resonance spectroscopic imaging using flyback echo planar readout trajectories

To present and evaluate a fast phosphorus magnetic resonance spectroscopic imaging (MRSI) sequence using echo planar spectroscopic imaging with flyback readout gradient trajectories.

Waveforms were designed and implemented using a 3 Tesla MRI system. ³¹P spectra were acquired with 2 × 2 cm² and 3 × 3 cm² resolution over a 20- and 21-cm field of view and spectral bandwidths up to 1923 Hz. The sequence was first tested using a 20-cm-diameter phosphate phantom, and subsequent in vivo tests were performed on healthy human calf muscles and brains from five volunteers.

Flyback EPSI achieved 10× and 7× reductions in acquisition time, with 68.0 ± 1.2 and 69.8 ± 2.2% signal-to-noise ratio (SNR) per unit of time efficiency (theoretical SNR efficiency was 74.5 and 76.4%) for the in vivo experiments, compared to conventional phase-encoded MRSI for the 2 × 2 cm² and 3 × 3 cm² resolution waveforms, respectively. Statistical analysis showed no difference in the quantification of most metabolites. Time savings and SNR comparisons were consistent across phantom, leg and brain experiments.

EPSI using flyback readout trajectories was found to be a reliable alternative for acquiring ³¹P-MRSI data in a shorter acquisition time.