人脑中水扩散的普适幂律标度定义了我们在MRI中看到的东西
Universal power-law scaling of water diffusion in human brain defines what we see with MRI
摘要：
神经系统疾病的成功疗法的开发取决于我们在细胞水平上诊断和监测潜在病理进展的能力。物理学和生理学将人类MRI的分辨率限制在毫米级，比微米级的细胞尺寸粗三个数量级。扩散加权MRI（dMRI）提供了一种有前途的访问细胞结构的方法，这种方法利用了MRI信号对受到细胞壁强烈阻碍的水分子的微米级布朗运动的敏感性。通过分析水分子在人体中的扩散，在这里，我们证明了生物物理建模有可能打破固有的MRI分辨率限制。对dMRI信号的普遍幂律缩放的观察确定了来自专门限制在狭窄的不可渗透轴突内的水的贡献，验证了神经元组织中扩散模型背后的总体假设。这种缩放行为确立了dMRI作为一种体内仪器，能够量化低于标称MRI分辨率的数量级的轴突内特性，促进了我们对大脑解剖结构和功能的理解。
英文摘要：
Development of successful therapies for neurological disorders depends on our ability to diagnose and monitor the progression of underlying pathologies at the cellular level. Physics and physiology limit the resolution of human MRI to millimeters, three orders of magnitude coarser than the cell dimensions of microns. A promising way to access cellular structure is provided by diffusion-weighted MRI (dMRI), a modality which exploits the sensitivity of the MRI signal to micron-level Brownian motion of water molecules strongly hindered by cell walls. By analyzing diffusion of water molecules in human subjects, here we demonstrate that biophysical modeling has the potential to break the intrinsic MRI resolution limits. The observation of a universal power-law scaling of the dMRI signal identifies the contribution from water specifically confined inside narrow impermeable axons, validating the overarching assumption behind models of diffusion in neuronal tissue. This scaling behavior establishes dMRI as an in vivo instrument able to quantify intra-axonal properties orders of magnitude below the nominal MRI resolution, spurring our understanding of brain anatomy and function.
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