Meyers Sandra M, Kolind Shannon H, MacKay Alex L
Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada.
Medicine, University of British Columbia, 2211 Wesbrook Mall, Vancouver, BC V6T 2B5, Canada.
Magn Reson Imaging. 2017 Apr;37:187-194. doi: 10.1016/j.mri.2016.12.001. Epub 2016 Dec 5.
This work demonstrates the in vivo application of a T relaxation based total water content (TWC) measurement technique at 3T in healthy human brain, and evaluates accuracy using simulations that model brain tissue. The benefit of using T relaxation is that it provides simultaneous measurements of myelin water fraction, which correlates to myelin content.
T relaxation data was collected from 10 healthy human subjects with a gradient and spin echo (GRASE) sequence, along with inversion recovery for T mapping. Voxel-wise T distributions were calculated by fitting the T relaxation data with a non-negative least squares algorithm incorporating B inhomogeneity corrections. TWC was the sum of the signals in the T distribution, corrected for T relaxation and receiver coil inhomogeneity, relative to either an external water standard or cerebrospinal fluid (CSF). Simulations were performed to determine theoretical errors in TWC.
TWC values measured in healthy human brain relative to both external and CSF standards agreed with literature values. Simulations demonstrated that TWC could be measured to within 3-4% accuracy.
In vivo TWC measurement using T relaxation at 3T works well and provides a valuable tool for studying neurological diseases with both myelin and water changes.
本研究展示了基于T弛豫的总含水量（TWC）测量技术在3T场强下对健康人脑的体内应用，并通过对脑组织建模的模拟来评估其准确性。使用T弛豫的好处在于它能同时测量髓鞘水分数，而髓鞘水分数与髓鞘含量相关。
采用梯度自旋回波（GRASE）序列以及用于T映射的反转恢复序列，从10名健康人体受试者收集T弛豫数据。通过使用结合B不均匀性校正的非负最小二乘算法拟合T弛豫数据，计算体素层面的T分布。TWC是T分布中信号的总和，相对于外部水标准或脑脊液（CSF）进行T弛豫和接收线圈不均匀性校正。进行模拟以确定TWC的理论误差。
相对于外部和CSF标准，在健康人脑中测量的TWC值与文献值一致。模拟表明，TWC的测量精度可达3 - 4%。
在3T场强下使用T弛豫进行体内TWC测量效果良好，为研究伴有髓鞘和水分变化的神经系统疾病提供了有价值的工具。
