Improved gradient echo magnitude- and phase-based mapping of T 2 $$ {\mathrm{T}}_2 $$ using multiple RF spoiling...

The transverse relaxation time T ${\hspace{0.17em}}_2$ holds significant relevance in clinical applications and research studies. Conventional T ${\hspace{0.17em}}_2$ mapping approaches rely on spin-echo sequences, which require lengthy acquisition times and involve high radiofrequency (RF) power deposition. An alternative gradient echo (GRE) phase-based T ${\hspace{0.17em}}_2$ mapping method, utilizing steady-state acquisitions at one small RF spoil phase increment, was recently demonstrated. Here, a modified magnitude- and phase-based T ${\hspace{0.17em}}_2$ mapping approach is proposed, which improves $T_2$ estimations by simultaneous fitting of $T_1$ and signal amplitude ( $A\propto PD$ ) at three or more RF spoiling phase increments, instead of assuming a fixed $T_1$ value.

The feasibility of the magnitude-phase-based method was assessed by simulations, in phantom and in vivo experiments using skipped-CAIPI three-dimensional-echo-planar imaging (3D-EPI) for rapid GRE imaging. $T_2$ , $T_1$ and PD estimations obtained by our method were compared to $T_2$ of the phase-based method and $T_1$ and PD of spoiled GRE-based multi-parameter mapping using a multi-echo version of the same sequence.

The agreement of the proposed $T_2$ with ground truth and reference $T_2$ values was higher than that of phase-based $T_2$ in simulations and in phantom data. While phase-based $T_2$ overestimation increases with actual $T_2$ and $T_1$ , the proposed method is accurate over a large range of physiologically meaningful $T_2$ and $T_1$ values. At the same time, precision is improved. In vivo results were in line with these observations.

Accurate magnitude-phase-based T ${\hspace{0.17em}}_2$ mapping is feasible in less than 5 min scan time for 1 mm nominal isotropic whole-head coverage at 3T and 7T.