McIlvain Grace
Department of Biomedical Engineering, College of Engineering and Applied Sciences, Columbia University, New York, NY 10027, USA.
Department of Radiology, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA.
Brain Commun. 2024 Dec 3;6(6):fcae424. doi: 10.1093/braincomms/fcae424. eCollection 2024.
Magnetic resonance elastography has emerged over the last two decades as a non-invasive method for quantitatively measuring the mechanical properties of the brain. Since the inception of the technology, brain stiffness has been the primary metric used to describe brain microstructural mechanics. However, more recently, a secondary measure has emerged as both theoretical and experimental significance, which is the ratio of tissue viscosity relative to tissue elasticity. This viscous-to-elastic ratio describes different but complementary aspects of brain microstructural health and is theorized to relate to microstructural organization, as opposed to stiffness, which is related to tissue composition. The relative viscosity of brain tissue changes regionally during maturation, aging and neurodegenerative disease. It also exhibits unique characteristics in brain tumours and hydrocephalus, and is of interest for characterizing traumatic head impacts. Most notably, regional measures of relative brain tissue viscosity appear to hold a unique role in describing cognitive function. For instance, in young adults, relatively lower hippocampal viscosity compared to elasticity repeatedly and sensitively relates to spatial, declarative and verbal memory performance. Importantly, these same trends are not found with hippocampal stiffness, or hippocampal volume, highlighting a potential sensitivity of relative viscosity to underlying cellularity that contributions to normal healthy brain function. Likewise in young adults, in the orbitofrontal cortex, lower relative viscosity relates to better performance on fluid intelligence tasks, and in the Broca's area of children ages 5-7, lower relative viscosity is indicative of better language performance. In these instances, this ratio shows heightened sensitivity over other structural MRI metrics, and importantly, provides a quantitative and intrinsic alternative to measuring structure-function relationships with task-based fMRI. There are ongoing efforts to improve the accuracy and repeatability of the relative viscosity measurement, and much work is needed to reveal the cellular underpinning of changes to tissue viscosity. But it appears clear that regionally measuring the viscous-to-elastic ratio holds the potential to noninvasively reveal an aspect of tissue microstructure that is clinically, cognitively and functionally relevant to our understanding of brain function and health.
在过去二十年中，磁共振弹性成像已成为一种用于定量测量大脑力学特性的非侵入性方法。自该技术问世以来，脑僵硬度一直是用于描述脑微观结构力学的主要指标。然而，最近出现了一种具有理论和实验意义的次要测量指标，即组织粘度与组织弹性的比值。这种粘弹性比值描述了脑微观结构健康的不同但互补的方面，理论上与微观结构组织有关，而僵硬度则与组织组成有关。脑组织的相对粘度在成熟、衰老和神经退行性疾病过程中会发生区域性变化。它在脑肿瘤和脑积水方面也表现出独特的特征，并且对于表征创伤性头部撞击很有意义。最值得注意的是，相对脑组织粘度的区域测量似乎在描述认知功能方面具有独特作用。例如，在年轻人中，与弹性相比，海马体相对较低的粘度反复且敏感地与空间、陈述性和言语记忆表现相关。重要的是，在海马体僵硬度或海马体体积方面未发现相同的趋势，这突出了相对粘度对潜在细胞结构的潜在敏感性，而这种细胞结构对正常健康的脑功能有贡献。同样在年轻人中，在眶额皮质，较低的相对粘度与流体智力任务的更好表现相关，而在5至7岁儿童的布洛卡区，较低的相对粘度表明语言表现更好。在这些情况下，该比值比其他结构磁共振成像指标表现出更高的敏感性，并且重要的是，为使用基于任务的功能磁共振成像测量结构 - 功能关系提供了一种定量和内在的替代方法。目前正在努力提高相对粘度测量的准确性和可重复性，并且需要做大量工作来揭示组织粘度变化的细胞基础。但很明显，区域测量粘弹性比值有可能非侵入性地揭示组织微观结构的一个方面，这在临床、认知和功能上与我们对脑功能和健康的理解相关。
