3T 和 7T 下磁化率各向异性对基于 T2*-的髓鞘水分数成像的影响。
Impact of magnetic susceptibility anisotropy at 3 T and 7 T on T2*-based myelin water fraction imaging.
机构信息
Medical Physics Unit, McGill University, 3801 University Street, Montreal, Quebec, H3A 2B4, Canada; McConnell Brain Imaging Centre, McGill University, 3801 University Street, Montreal, Quebec, H3A 2B4, Canada.
Medical Physics Unit, McGill University, 3801 University Street, Montreal, Quebec, H3A 2B4, Canada; Gerald Bronfman Department of Oncology, McGill University, 3801 University Street, Montreal, Quebec, H3A 2B4, Canada; Research Institute of the McGill University Health Centre, McGill University, 3801 University Street, Montreal, Quebec, H3A 2B4, Canada.
出版信息
Neuroimage. 2018 Nov 15;182:370-378. doi: 10.1016/j.neuroimage.2017.09.040. Epub 2017 Sep 25.
PURPOSE
Myelin Water Fraction (MWF) mapping can be achieved by fitting multi-gradient recalled echo (MGRE) magnitude images with a three-component model or a pseudo-continuous T distribution. Recent findings of compartment-specific orientation-dependent magnetic susceptibility shifts have spurred the inclusion of frequency offset (Δf) terms in the fitting models. In this work, we performed simulations to assess the impact of Δf's on the MWF, derived from three different fitting models, at two field strengths.
THEORY AND METHODS
White matter MGRE signals were simulated using the Hollow Cylinder Fiber Model at 3 and 7 T, for a range of fiber orientations (θ), and analyzed using: 1) a multi-component T signal magnitude model (MCMT); 2) a three-component T signal magnitude model (3CMT); and, 3) a three-component complex T signal model (3CCT).
RESULTS
At 3 T, MCMT & 3CMT yielded accurate MWFs: (11.9±1.1)% and (11.7±1.0)% (mean± standard deviation across 1000 simulations, true MWF = 12%), respectively. 3CCT MWFs were less accurate and had the largest variability: (9.2±5.0)%. At 7 T, MCMT and 3CMT MWFs became less accurate as θ increased. This was remedied by 3CCT, at the expense of accuracy for small θ.
CONCLUSION
This work suggests that if no information regarding Δf is sought, MCMT and 3CMT are preferable at 3 T. At 7 T, Δf cannot be overlooked.
目的
通过拟合多梯度回波（MGRE）幅度图像的三组分模型或伪连续 T 分布，可以获得髓鞘水分数（MWF）图。最近发现的各向异性磁敏感位移的分室特异性促使在拟合模型中包含频率偏移（Δf）项。在这项工作中，我们进行了模拟，以评估在两个场强下，来自三个不同拟合模型的 Δf 对 MWF 的影响。
理论和方法
在 3 和 7 T 下，使用空心圆柱纤维模型模拟白质 MGRE 信号，针对一系列纤维取向（θ）进行分析，并使用：1）多组分 T 信号幅度模型（MCMT）；2）三组分 T 信号幅度模型（3CMT）；和 3）三组分复 T 信号模型（3CCT）进行分析。
结果
在 3 T 下，MCMT 和 3CMT 产生了准确的 MWF：（11.9±1.1）%和（11.7±1.0）%（1000 次模拟的平均值±标准偏差，真实 MWF=12%）。3CCT 的 MWF 不太准确，且变异性最大：（9.2±5.0）%。在 7 T 下，随着θ的增加，MCMT 和 3CMT 的 MWF 变得不太准确。这可以通过 3CCT 来纠正，但代价是小θ的准确性。
结论
这项工作表明，如果不寻求有关Δf 的信息，则在 3 T 时，MCMT 和 3CMT 是首选。在 7 T 时，不能忽略Δf。
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