Abstract：
OBJECTIVE: 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.
CONCLUSIONS: 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.
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.
CONCLUSIONS: 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.
摘要：
目的：横向弛豫时间T2$${}_2$$$在临床应用和研究中具有重要意义。传统的T2$${}_2$$映射方法依赖于自旋回波序列，这需要较长的采集时间并且涉及高射频(RF)功率沉积。一种基于梯度回波(GRE)相位的T2$${}_2$$映射方法，在一个小的RF弃渣相位增量下利用稳态采集，最近被证明。这里,提出了一种改进的基于幅度和相位的T2$${}_2$$映射方法，通过同时拟合T1$${\\mathrm{T}}_1$$和信号幅度(APPOPD$$A\\proptoPD$$$),改进了T2$$${\\mathrm{T}}_2$$$估计,而不是假设一个固定的T1$${\\mathrm{T}}_1$$值。
方法：通过模拟评估了基于幅度相位的方法的可行性，在体模和体内实验中，使用跳过的CAIPI三维回波平面成像（3D-EPI）进行快速GRE成像。T2$${\\mathrm{T}}_2$$,通过我们的方法获得的T1$${\\mathrm{T}}_1$$和PD估计与基于相位的方法的T2${\\mathrm{T}}_2$$和T1$${\\mathrm{T}}_1$$$和PD使用相同序列的多回声版本进行了比较。
结果：建议的T2$${\\mathrm{T}}_2$$与实际值和参考T2$${\\mathrm{T}}_2$$$的一致性高于基于相位的T2$$${\\mathrm{T}}_2$$$$在模拟和幻影数据中的一致性。虽然基于阶段的T2$${\\mathrm{T}}_2$$过估计随着实际的T2${\\mathrm{T}}_2$$和T1$${\\mathrm{T}}_1$$$而增加，所提出的方法在大范围的有生理意义的T2$${\\mathrm{T}}_2$$和T1${\\mathrm{T}}_1$$值上是准确的。同时,精度得到提高。体内结果与这些观察结果一致。
结论：在3T和7T下，在小于5分钟的扫描时间内，基于幅度相位的精确T2$${}_2$$$映射是可行的，用于1mm标称各向同性全头覆盖。
方法：通过模拟评估了基于幅度相位的方法的可行性，在体模和体内实验中，使用跳过的CAIPI三维回波平面成像（3D-EPI）进行快速GRE成像。T2$${\\mathrm{T}}_2$$,通过我们的方法获得的T1$${\\mathrm{T}}_1$$和PD估计与基于相位的方法的T2${\\mathrm{T}}_2$$和T1$${\\mathrm{T}}_1$$$和PD使用相同序列的多回声版本进行了比较。
结果：建议的T2$${\\mathrm{T}}_2$$与实际值和参考T2$${\\mathrm{T}}_2$$$的一致性高于基于相位的T2$$${\\mathrm{T}}_2$$$$在模拟和幻影数据中的一致性。虽然基于阶段的T2$${\\mathrm{T}}_2$$过估计随着实际的T2${\\mathrm{T}}_2$$和T1$${\\mathrm{T}}_1$$$而增加，所提出的方法在大范围的有生理意义的T2$${\\mathrm{T}}_2$$和T1${\\mathrm{T}}_1$$值上是准确的。同时,精度得到提高。体内结果与这些观察结果一致。
结论：在3T和7T下，在小于5分钟的扫描时间内，基于幅度相位的精确T2$${}_2$$$映射是可行的，用于1mm标称各向同性全头覆盖。
