A new ultrafast 3D gradient echo-based imaging method using quadratic-phase encoding

Purpose: To propose a novel 3D ultrafast gradient echo-based MRI method, dubbed RASE, using quadratic-phase encoding. Theory and Methods: Several characteristics of RASE, including spin behaviors, spatial resolution, SNR, and reduction of susceptibility-induced signal loss, were analytically described. A way of compensating for TE variation was suggested in the quadratic phase-encoding direction. Lemon, in vivo rat and mouse images were demonstrated at 9.4T, including a feasibility study for DCE-MRI as one of promising applications. Results: RASE was successfully demonstrated by lemon and in vivo rat brain imaging, showing a good robustness to field inhomogeneity. Contribution of the quadratic phase to signal enhancement in a range of magnetic susceptibilities was also evaluated by simulation. Taking a geometric mean of 2 phantom data acquired with opposite gradient polarities effectively compensated for the effect of TE variation. Preliminary DCE-MRI results were also presented, showing that RASE could more accurately estimate Gd concentration than FLASH. Conclusion: RASE offers a shorter effective TE, having less sensitivity to field inhomogeneity and T₂^* effects, much less Nyquist ghosting or chemical-shift artifacts than gradient echo EPI (GE-EPI). We highly anticipate that RASE can be an alternative to GE-EPI in many applications, particularly those requiring high spatial and temporal resolutions in a broad volume coverage.