Quantitative Magnetic Resonance Imaging of Anisotropic Biological Tissues

各向异性生物组织的定量磁共振成像

• 批准号: RGPIN-2021-04085
• 负责人: Rauscher, Alexander
• 金额: $ 2.99万
• 依托单位: University of British Columbia
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=761985
• 关键词: Quantitative; Magnetic; Resonance; Imaging; Anisotropic

Magnetic resonance imaging (MRI) has become a powerful tool for the investigation of the central nervous system. Intense efforts are underway to develop quantitative MRI methods specific for particular components of biological tissue. Over the past five years, my students and I have investigated how quantitative MRI methods, such as myelin water imaging or perfusion image depend on tissue composition and tissue architecture and its orientation relative to the main magnetic field. We found that perfusion measurements are strongly influenced by tissue orientation since about half of the blood in the brain is in blood vessels that run in parallel with the brain's nerve fibre tracts. Depending on the MRI technique, the effect is up to 100% difference between white matter tissue that runs parallel to the magnetic field and tissue that runs perpendicular to the magnetic field. We developed numerical methods that allowed us to determine the blood volume in the brain's white matter, with high agreement between positron emission tomography (the gold standard) and our MRI approaches. For the myelin water fraction determined with a multi echo spin echo scan, we also found a systematic orientation effect of 30% between the lowest values and the highest values. The reasons for this effect are not clear. Dipole-dipole interactions as well as the magnetic susceptibility of the myelin sheath could contribute to the effect. During the next five years of my research program I will continue to investigate these orientation effects in order to contribute to our understanding of MRI signal generation. I will analyse myelin water data acquired in the non-myelinated human newborn brain and in myelinated and demyelinated post mortem tissue before and after fixation and develope numerical tissue models. From this work we will gain insights into the role of myelin on the orientation effects and how tissue fixation may have obscured orientation effects in previous post mortem studies. Furthermore, we have embarked on machine learning approaches to recover meaningful information from MRI scans. Normally, machine learning relies on large amounts of training data. With our understanding of magnetic resonance image generation, we are in the position to compute arbitrary amounts of synthetic training data. Neural networks trained on such synthetic data are able to solve problems encountered in real data, often with no or minimal additional training on real data. We will train two neural networks that will help us overcome barriers to the broader applicability of our quantitative methods. One network will determine tissue orientation from a conventional anatomical scan that is part of almost every brain MRI protocol. The other network will learn the noise distribution of the data in order to perform much improved parameter inference.

磁共振成像（MRI）已成为研究中枢神经系统的有力工具。目前正在加紧努力开发针对生物组织特定成分的定量MRI方法。在过去的五年里，我和我的学生研究了定量MRI方法，如髓鞘水成像或灌注成像如何取决于组织成分和组织结构及其相对于主磁场的方向。我们发现灌注测量受到组织方向的强烈影响，因为大脑中大约一半的血液位于与大脑神经纤维束平行的血管中。根据MRI技术，平行于磁场的白色组织和垂直于磁场的组织之间的影响差异高达100%。我们开发了数值方法，使我们能够确定大脑白色物质中的血容量，正电子发射断层扫描（金标准）和我们的MRI方法之间具有高度一致性。 对于髓磷脂水分数确定与多回波自旋回波扫描，我们还发现了一个系统的方向效应的最低值和最高值之间的30%。造成这种影响的原因尚不清楚。偶极-偶极相互作用以及髓鞘的磁化率可能有助于这种效应。在未来五年的研究计划中，我将继续研究这些方向效应，以促进我们对MRI信号产生的理解。我将分析在无髓鞘的人类新生儿大脑和有髓鞘和脱髓鞘的死后组织固定前后获得的髓鞘水数据，并开发数值组织模型。从这项工作中，我们将获得深入了解髓鞘的作用的方向效果，以及如何组织固定可能掩盖了方向的影响，在以前的死后研究。 此外，我们已经开始使用机器学习方法从MRI扫描中恢复有意义的信息。通常，机器学习依赖于大量的训练数据。随着我们对磁共振图像生成的理解，我们能够计算任意数量的合成训练数据。在这样的合成数据上训练的神经网络能够解决在真实的数据中遇到的问题，通常不需要对真实的数据进行额外的训练或进行最少的额外训练。我们将训练两个神经网络，帮助我们克服量化方法更广泛适用性的障碍。其中一个网络将通过常规解剖扫描确定组织方向，这是几乎所有大脑MRI协议的一部分。另一个网络将学习数据的噪声分布，以执行更好的参数推断。