van Gelderen Peter, Jiang Xu, Duyn Jeff H
Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
Neuroimage. 2016 Mar;128:85-95. doi: 10.1016/j.neuroimage.2015.12.032. Epub 2015 Dec 24.
MRI based on T1 relaxation contrast is increasingly being used to study brain morphology and myelination. Although it provides for excellent distinction between the major tissue types of gray matter, white matter, and CSF, reproducible quantification of T1 relaxation rates is difficult due to the complexity of the contrast mechanism and dependence on experimental details. In this work, we perform simulations and inversion-recovery MRI measurements at 3T and 7T to show that substantial measurement variability results from unintended and uncontrolled perturbation of the magnetization of MRI-invisible (1)H protons of lipids and macromolecules. This results in bi-exponential relaxation, with a fast component whose relative contribution under practical conditions can reach 20%. This phenomenon can strongly affect apparent relaxation rates, affect contrast between tissue types, and result in contrast variations over the brain. Based on this novel understanding, ways are proposed to minimize this experimental variability and its effect on T1 contrast, quantification accuracy and reproducibility.
基于T1弛豫对比度的磁共振成像（MRI）越来越多地用于研究脑形态和髓鞘形成。尽管它能很好地区分灰质、白质和脑脊液等主要组织类型，但由于对比度机制的复杂性以及对实验细节的依赖性，T1弛豫率的可重复量化很困难。在这项工作中，我们在3T和7T下进行了模拟和反转恢复MRI测量，以表明大量测量变异性源于脂质和大分子的MRI不可见（1）H质子磁化的意外和不受控制的扰动。这导致双指数弛豫，其快速成分在实际条件下的相对贡献可达20%。这种现象会强烈影响表观弛豫率，影响组织类型之间的对比度，并导致大脑对比度变化。基于这一新认识，我们提出了一些方法来最小化这种实验变异性及其对T1对比度、量化准确性和可重复性的影响。
