Anisotropy effects of the magnetic resonance signal of biological tissue.

磁共振成像(MRI)是一种无创、多功能的成像技术，在研究和诊断方面取得了巨大的成功。有了先进的核磁共振成像，人们可以探测生物组织，使研究人员能够创建组织属性的量化地图。MRI评估的特征包括信号松弛、细胞代谢物浓度、水扩散或血流的数量和方向。近年来的研究表明，一些磁共振成像技术对各向异性组织的主轴与磁场方向之间的夹角很敏感。例如，已经特别针对R2*信号弛豫的图像描述了系统取向相关性(OD)，由当前数学模型将其归因于各向同性和各向异性组织两者的贡献。如果理解得很好，这些效应可能被用来绘制早期大脑发育或组织损伤和修复的图谱。*拟议的计划侧重于通过各种MRI技术调查OD及其潜在来源。我们的具体目标是：*1.研究R2*松弛的OD与吸入混合气体调节的静脉血氧代谢之间的关系。较大的血管最好与大脑白质的神经纤维束平行运行。因此，这些血管中的脱氧血液增加了白质中R2*的方位依赖性。在不同程度的静脉血氧分压下获取R2*MAP将使我们能够更详细地研究这些影响。*2.研究对比剂脑灌注成像获得的脑血流和血容量图如何受白质方位的影响。我们将分析用梯度回波和自旋回波扫描获得的灌注图，以评估对MR数据采集的依赖性，并对空间各向异性血管网络进行数值模拟。*3.研究髓鞘水图如何依赖于WM纤维取向(体内和体外)。*4.研究R2*松弛的外径在出生后的头几个月是如何演变的。*由于髓鞘水灌注成像和血液氧合成像被广泛使用，了解它们的局限性是至关重要的。此外，角度分辨分析可能允许检测常规分析可能失败的脑组织的变化。

Magnetic Resonance Imaging (MRI) is a non-invasive and versatile imaging technique, which has seen tremendous success in research and diagnosis. With advanced MRI, one can probe biological tissues in ways that allow researchers to create quantitative maps of tissue properties. Characteristics assessed with MRI include the signal relaxation, the concentration of cell metabolites, and the amount and direction of water diffusion or blood flow. In recent years it has been shown that some MRI techniques are sensitive to the angle formed between the main axis of anisotropic tissues and the direction of the magnetic field. For instance, a systematic orientation dependency (OD) has been described in particular for images of R2* signal relaxation, attributed by current mathematical models to the contributions of both isotropic and anisotropic tissues. If understood well, these effects may be used to map early brain development or tissue damage and repair. ******The proposed program focuses on the investigation of the OD and its underlying origin across various MRI techniques. Our specific aims are: ******1. To investigate how the OD of R2* relaxation relates to venous blood oxygenation modulated via the inhalation of gas mixtures. Larger blood vessels run preferably in parallel with nerve fibre tracts of the brain's white matter. Therefore, deoxygenated blood in these vessels adds to the orientation dependency of R2* in white matter. Acquisition of R2* maps at varous degrees of venous blood oxygenation will allow us to investigate these effects in more detail. ******2. To investigate how cerebral blood flow and blood volume maps acquired with contrast-agent-based perfusion imaging are influenced by the orientation of white matter (WM). We will analyze perfusion maps acquired with gradient echo and spin echo scans to evaluate the dependency on MR data acquisition and perform numerical simulations of spatially anisotropic vascular networks. ******3. To investigate how myelin water maps depend on WM fibre orientation (both in vivo and ex vivo). ******4. To investigate how the OD of R2* relaxation evolves in the first months after birth. ******Since imaging of perfusion myelin water and blood oxygenation are used widely, it is vital to understand their limitations. Moreover, angle resolved analysis may allow for the detection of change in brain tissue where conventional analyses may fail.