Wang Difei, Stirnberg Rüdiger, Stöcker Tony
MR Physics, German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
Department of Physics & Astronomy, University of Bonn, Bonn, Germany.
Magn Reson Med. 2024 Dec;92(6):2328-2342. doi: 10.1002/mrm.30217. Epub 2024 Jul 10.
The transverse relaxation time T holds significant relevance in clinical applications and research studies. Conventional T 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 mapping method, utilizing steady-state acquisitions at one small RF spoil phase increment, was recently demonstrated. Here, a modified magnitude- and phase-based T mapping approach is proposed, which improves estimations by simultaneous fitting of and signal amplitude ( ) at three or more RF spoiling phase increments, instead of assuming a fixed 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. , and PD estimations obtained by our method were compared to of the phase-based method and and PD of spoiled GRE-based multi-parameter mapping using a multi-echo version of the same sequence.
The agreement of the proposed with ground truth and reference values was higher than that of phase-based in simulations and in phantom data. While phase-based overestimation increases with actual and , the proposed method is accurate over a large range of physiologically meaningful and values. At the same time, precision is improved. In vivo results were in line with these observations.
Accurate magnitude-phase-based T mapping is feasible in less than 5 min scan time for 1 mm nominal isotropic whole-head coverage at 3T and 7T.
横向弛豫时间T在临床应用和研究中具有重要意义。传统的T映射方法依赖于自旋回波序列，该序列需要较长的采集时间且涉及高射频（RF）功率沉积。最近展示了一种基于梯度回波（GRE）相位的T映射方法，该方法利用在一个小的RF扰相相位增量下的稳态采集。在此，提出了一种改进的基于幅度和相位的T映射方法，该方法通过在三个或更多RF扰相相位增量下同时拟合T和信号幅度（ ）来改进T估计，而不是假设一个固定的 值。
通过模拟、体模实验以及在体实验评估基于幅度 - 相位方法的可行性，在体实验使用跳跃式CAIPI三维回波平面成像（3D - EPI）进行快速GRE成像。将我们的方法获得的T、 和质子密度（PD）估计值与基于相位方法的T以及使用相同序列的多回波版本的扰相GRE多参数映射的T和PD进行比较。
在模拟和体模数据中，所提出的T与真实值和参考T值的一致性高于基于相位的T。虽然基于相位的T高估随着实际T和 的增加而增加，但所提出的方法在生理上有意义的T和 值的较大范围内是准确的。同时，精度得到提高。在体结果与这些观察结果一致。
基于幅度 - 相位的准确T映射在3T和7T下以小于5分钟的扫描时间对1mm标称各向同性全脑覆盖是可行的。
