Improved gradient echo magnitude- and phase-based mapping of T 2 $$ {\mathrm{T}}_2 $$ using multiple RF spoiling increments at 3T and 7T.

ABSTRACT

PURPOSE: The transverse relaxation time T 2 $$ {}_2 $$ holds significant relevance in clinical applications and research studies. Conventional T 2 $$ {}_2 $$ 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 2 $$ {}_2 $$ mapping method, utilizing steady-state acquisitions at one small RF spoil phase increment, was recently demonstrated. Here, a modified magnitude- and phase-based T 2 $$ {}_2 $$ mapping approach is proposed, which improves T 2 $$ {\mathrm{T}}_2 $$ estimations by simultaneous fitting of T 1 $$ {\mathrm{T}}_1 $$ and signal amplitude ( A ∝ P D $$ A\propto PD $$ ) at three or more RF spoiling phase increments, instead of assuming a fixed T 1 $$ {\mathrm{T}}_1 $$ value. METHODS: 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 $$ {\mathrm{T}}_2 $$ , T 1 $$ {\mathrm{T}}_1 $$ and PD estimations obtained by our method were compared to T 2 $$ {\mathrm{T}}_2 $$ of the phase-based method and T 1 $$ {\mathrm{T}}_1 $$ and PD of spoiled GRE-based multi-parameter mapping using a multi-echo version of the same sequence. RESULTS: The agreement of the proposed T 2 $$ {\mathrm{T}}_2 $$ with ground truth and reference T 2 $$ {\mathrm{T}}_2 $$ values was higher than that of phase-based T 2 $$ {\mathrm{T}}_2 $$ in simulations and in phantom data. While phase-based T 2 $$ {\mathrm{T}}_2 $$ overestimation increases with actual T 2 $$ {\mathrm{T}}_2 $$ and T 1 $$ {\mathrm{T}}_1 $$ , the proposed method is accurate over a large range of physiologically meaningful T 2 $$ {\mathrm{T}}_2 $$ and T 1 $$ {\mathrm{T}}_1 $$ values. At the same time, precision is improved. In vivo results were in line with these observations. CONCLUSION: Accurate magnitude-phase-based T 2 $$ {}_2 $$ mapping is feasible in less than 5 min scan time for 1 mm nominal isotropic whole-head coverage at 3T and 7T.