Simulating extravascular artifacts surrounding cortical draining veins to increase neuronal specificity of ultra-high-field fMRI

模拟皮质引流静脉周围的血管外伪影以提高超高场功能磁共振成像的神经元特异性

• 批准号: 388285513
• 负责人: Dr. Jörg Pfannmöller
• 金额: --
• 依托单位: Institut für Diagnostische Radiologie und Neuroradiologie
• 依托单位国家: 德国
• 项目类别: Research Fellowships
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/388285513?language=en
• 关键词: Simulating; extravascular; artifacts; surrounding; cortical

fMRI is the most commonly used imaging method for non-invasively mapping brain function in humans. Modern MRI technology has provided imaging methods with unprecedentedly high spatio-temporal resolution, enabling fMRI investigations which are dramatically enhancing our knowledge about the working human brain. All fMRI techniques seek to infer patterns of neuronal activity by measuring the accompanying changes in blood supply. The most commonly used fMRI signal is the blood oxygen level dependent or BOLD contrast, which is typically acquired with gradient echo MRI sequences. This technique provides the most sensitive and robust fMRI measurement and is therefore well suited to exploit the available spatio-temporal imaging resolution. However, a major problem that limits the ability of gradient-echo BOLD to infer underlying neuronal activity is the degradation of the spatial specificity due to artifacts given by signal displacement from draining veins at the cortical surface and from intra cortical veins. Those artifacts can be discounted using a priori knowledge of the functional architecture in combination with careful experimental design, which provided sufficient specificity to detect neuronal activation across the cerebral cortical layers. The prospect of “laminar fMRI” has spurred recent interest in methods designed to account for these artifacts that limit BOLD fMRI by combining knowledge about the cortical vascularization, which is strikingly regular and consistent across the cortex, with models of how the fMRI signal is influenced by draining veins. Here we propose to adapt the Ogawa/Boxerman model to simulate the intravascular and extravascular gradient-echo BOLD signals for a broadly applicable removal of draining vein artifacts to improve resolution. Our new implementation will first be benchmarked against previous simulations and estimations of the artifact. In a second step the model for artifact removal will be constructed after the calibration of the simulation. Subsequently, we validate our artifact range and voxel size based model for artifact removal in an independent sample. Calibration and validation will be carried out using fMRI data of a well-known topographic map in the primary visual cortex acquired at 3T and 7T. This serves as a proof for our hypothesis that accounting for the extravascular signal can improve the neuronal specificity of fMRI. Currently, several endeavors are underway to construct next generation MRI scanners with field strengths up to 20T, paving the way for future decreases in fMRI voxel sizes. However, the artifact ranges and magnitudes increase together with MR field strength. Thus, careful modeling of the relationship between neuronal activity and the observed hemodynamic signals underlying fMRI measures will be even more important to exploit these future technologies. Therefore, we will use our simulations to predict the spatial resolution and the maximum achievable specificity from 3 to 20 Tesla.

功能磁共振成像是最常用的成像方法，用于非侵入性映射人类大脑功能。现代MRI技术为成像方法提供了前所未有的高时空分辨率，使fMRI研究大大提高了我们对人脑工作的了解。所有的功能磁共振成像技术都试图通过测量伴随的血液供应变化来推断神经元活动的模式。最常用的fMRI信号是血氧水平依赖性或BOLD对比度，通常使用梯度回波MRI序列采集。这种技术提供了最灵敏和强大的功能磁共振成像测量，因此非常适合利用现有的时空成像分辨率。然而，限制梯度回波BOLD推断潜在神经元活动的能力的一个主要问题是由于来自皮质表面处的引流静脉和来自皮质内静脉的信号位移所给出的伪影导致的空间特异性的退化。使用功能结构的先验知识并结合仔细的实验设计，可以消除这些伪影，这为检测大脑皮质层的神经元激活提供了足够的特异性。“层状功能磁共振成像”的前景最近激发了人们的兴趣，他们设计了一些方法来解释这些限制BOLD功能磁共振成像的伪影，这些方法结合了关于皮质血管化的知识，这些血管化在整个皮质中是惊人的规则和一致的，以及功能磁共振成像信号如何受到引流静脉影响的模型。 在这里，我们建议调整Ogawa/Boxerman模型来模拟血管内和血管外梯度回波BOLD信号，以广泛适用于去除引流静脉伪影，以提高分辨率。我们的新实现将首先根据以前的模拟和工件的估计进行基准测试。在第二步骤中，将在模拟的校准之后构建用于伪影去除的模型。随后，我们验证了我们的伪影范围和体素大小为基础的模型，在一个独立的样本中去除伪影。校准和验证将使用功能磁共振成像数据的一个众所周知的地形图在初级视觉皮层在3 T和7 T采集。这为我们的假设提供了证据，即考虑血管外信号可以提高fMRI的神经元特异性。目前，正在努力构建下一代MRI扫描仪，其场强高达20 T，为未来fMRI体素尺寸的减小铺平了道路。然而，伪影范围和幅度随着MR场强的增加而增加。因此，仔细建模神经元活动和所观察到的血流动力学信号之间的关系的fMRI措施将更加重要的利用这些未来的技术。因此，我们将使用我们的模拟来预测3到20特斯拉的空间分辨率和最大可实现的特异性。