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Abstract：
The multicomponent relaxation observed in nuclear magnetic resonance experiments in biological tissues makes it difficult to establish a correlation between specific relaxation times and tissue structural parameters. The analysis of a nanostructure (the characteristic size of 10-1000 nm) is usually based on formulas for relaxation times which depend on structural parameters at the atomic or molecular levels in the size range of 0.1-5 nm. We have recently developed an analysis method in which relaxation times\' anisotropy in a sample is explicitly related to its structure of nanocavities containing a liquid or gas. However, the method is based on the analysis of experimental data on the anisotropy of relaxation times obtained by using the standard NMR technique and rotating the sample relative to a magnetic field and requires a series of experiments. In the present study, to address this challenge, we develop a new method of analysis of a multi-exponential magnetic resonance signal that does not require determining relaxation times and eliminates the sample rotation and the necessity of a series of experiments. Using the magnetic resonance imaging (MRI) technique, the total signal from the whole sample was obtained as a sum of the signals (echo decays) from all voxels. In contrast to previous research, the volumes of nanocavities and their angular distribution can be obtained by analyzing a single total signal for the entire cartilage. In addition, within the framework of this approach, it is possible to identify the reason for the multicomponent nature of relaxation. The proposed method for analyzing a single multi-exponential signal (transverse relaxation) was implemented on cartilage. Using the signal, three anatomical zones of cartilage were studied, revealing significant structural differences between them. The proposed method not only avoids the need for sample rotation but also enables repeated application of layer-by-layer magnetic resonance imaging with micron resolution. The study results allow us to suggest that water molecules contributing to the echo decay are more likely located in nanocavities formed by the fibrillar structure rather than inside the fibrils.
摘要：
在生物组织的核磁共振实验中观察到的多组分弛豫使得难以建立特定弛豫时间与组织结构参数之间的相关性。纳米结构（特征尺寸为10-1000nm）的分析通常基于弛豫时间的公式，该公式取决于0.1-5nm尺寸范围内原子或分子水平的结构参数。我们最近开发了一种分析方法，其中样品中的弛豫时间各向异性与包含液体或气体的纳米腔的结构明确相关。然而,该方法基于对使用标准NMR技术并相对于磁场旋转样品获得的弛豫时间各向异性的实验数据的分析，需要进行一系列实验。在本研究中,为了应对这一挑战，我们开发了一种分析多指数磁共振信号的新方法，该方法不需要确定弛豫时间，并且消除了样品旋转和一系列实验的必要性。使用磁共振成像（MRI）技术，作为来自所有体素的信号(回波衰减)的总和,获得来自整个样本的总信号。与以前的研究相比，可以通过分析整个软骨的单个总信号来获得纳米腔的体积及其角分布。此外,在这种方法的框架内，可以确定松弛的多组分性质的原因。所提出的用于分析单个多指数信号（横向松弛）的方法在软骨上实施。使用信号，研究了软骨的三个解剖区，揭示了它们之间显著的结构差异。所提出的方法不仅避免了样品旋转的需要，而且能够重复应用具有微米分辨率的逐层磁共振成像。研究结果使我们能够表明，导致回波衰减的水分子更有可能位于由原纤维结构形成的纳米腔中，而不是原纤维内部。
