University of Applied Sciences Koblenz, RheinAhrCampus Remagen, 53424 Remagen, Germany.
Z Med Phys. 2012 Jun;22(2):133-42. doi: 10.1016/j.zemedi.2011.09.005. Epub 2011 Oct 22.
We present an algorithm for the fast mapping of myelin water content using standard multiecho gradient echo acquisitions of the human brain. The method extents a previously published approach for the simultaneous measurement of brain T(1), T(2)() and total water content. Employing the multiexponential T(2)() decay signal of myelinated tissue, myelin water content was measured based on the quantification of two water pools ("myelin water" and "rest") with different relaxation times. As the existing protocol was focussed on the fast mapping of quantitative MR parameters with whole brain coverage in clinically relevant measurement times, the sampling density of the T(2)() curve was compromised to 10 echo times with a TE(max) of approx. 40ms. Therefore, pool amplitudes were determined using a quadratic optimisation approach. The optimisation was constrained by including à priori knowledge about brain water pools. All constraints were optimised in a simulation study to minimise systematic error sources given the incomplete knowledge about the real pool-specific relaxation properties. Based on the simulation results, whole brain in vivo myelin water content maps were acquired in 10 healthy controls and one subject with multiple sclerosis. The in vivo results obtained were consistent with previous reports which demonstrates that a simultaneous whole brain mapping of T(1), T(2)(), total and myelin water content is feasible on almost any modern MR scanner in less than 10 minutes.
我们提出了一种使用标准多回波梯度回波采集人脑的髓鞘水含量快速映射算法。该方法扩展了以前发表的同时测量脑 T1、T2()和总含水量的方法。利用有髓组织的多指数 T2()衰减信号，根据弛豫时间不同的两个水池（“髓鞘水”和“剩余水”）的定量，测量髓鞘水含量。由于现有方案侧重于在临床相关测量时间内用全脑覆盖快速映射定量 MR 参数，因此 T2()曲线的采样密度以 10 个回波时间妥协，最大 TE（约 40ms）。因此，使用二次优化方法确定池幅度。通过包括关于脑水池的先验知识来约束优化。所有约束都在模拟研究中进行了优化，以在对真实池特定弛豫特性的不完全了解的情况下最小化系统误差源。基于模拟结果，在 10 名健康对照者和 1 名多发性硬化症患者中获得了整个大脑的髓鞘水含量图。体内结果与先前的报告一致，证明在不到 10 分钟的时间内在几乎任何现代磁共振扫描仪上都可以进行 T1、T2()、总水和髓鞘水含量的全脑同时映射是可行的。
