A new ultrafast 3D gradient echo‐based imaging method usingquadratic‐phase encoding

Abstract

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.© 2019 International Society for Magnetic Resonance in Medicine.