Magnetization transfer explains most of the T 1 variability in the MRI literature.

ArXiv Pub Date : 2024-11-24
Jakob Assländer, Sebastian Flassbeck
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引用次数: 0

Abstract

Purpose: To identify the predominant source of the T 1 variability described in the literature, which ranges from 0.6-1.1 s for brain white matter at 3 T.

Methods: 25 T 1 -mapping methods from the literature were simulated with a mono-exponential and various magnetization-transfer (MT) models, each followed by mono-exponential fitting. A single set of model parameters was assumed for the simulation of all methods, and these parameters were estimated by fitting the simulation based to the corresponding literature T 1 values of white matter at 3 T. In vivo MT parameter maps were further used to synthesize MR images for 3 T 1 -mapping methods. A mono-exponential model was fitted to the synthesized and corresponding experimental MR images.

Results: Mono-exponential simulations suggest good inter-method reproducibility and fail to explain the highly variable T 1 estimates in the literature. In contrast, MT simulations suggest that a mono-exponential fit results in a variable T 1 and explain up to 62% of the literature's variability. In our own in vivo experiments, MT explains 70% of the observed variability.

Conclusion: The results suggest that a mono-exponential model does not adequately describe longitudinal relaxation in biological tissue. Therefore, T 1 in biological tissue should be considered only a semi-quantitative metric that is inherently contingent upon the imaging methodology; and comparisons between different T 1 -mapping methods and the use of simplistic spin systems-such as doped-water phantoms-for validation should be viewed with caution.

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磁化传递可以解释磁共振成像文献中大部分的 $T_1$ 变异。
目的:确定文献中描述的$T_1$变异性的主要来源,文献中描述的脑白质在 3 T 下的$T_1$变异性范围为 0.6 - 1.1 秒。方法:用单指数模型和磁化转移(MT)模型模拟文献中的 25 种$T_1$绘图方法,每种方法都进行了单指数拟合。所有方法的模拟都假定有一组模型参数,这些参数是通过将模拟结果与相应文献中 3 T 白质的 $T_1$ 值进行拟合而估算出来的:单指数模拟表明方法间具有良好的可重复性,但无法解释文献中高度多变的 T_1$ 估计值。与此相反,MT 模拟表明单指数拟合会产生可变的 $T_1$,并能解释文献中高达 62% 的可变性:结果表明,单指数模型不能充分描述生物组织的纵向弛豫。因此,生物组织中的 $T_1$ 只应被视为一种半定量指标,其本身取决于成像方法;应谨慎看待不同 $T_1$ 绘图方法之间的比较以及使用简单自旋系统(如掺水模型)进行验证。
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