Anisotropy effects of the magnetic resonance signal of biological tissue.

磁共振成像（MRI）是一种非侵入性、多功能的成像技术，在研究和诊断方面取得了巨大的成功。借助先进的 MRI，研究人员可以探测生物组织，从而创建组织特性的定量图。 MRI 评估的特征包括信号弛豫、细胞代谢物的浓度以及水扩散或血流的数量和方向。近年来，已经表明一些MRI技术对各向异性组织的主轴线与磁场方向之间形成的角度敏感。例如，特别针对 R2* 信号弛豫图像描述了系统方向依赖性 (OD)，通过当前数学模型将其归因于各向同性和各向异性组织的贡献。如果理解得当，这些效应可以用来绘制早期大脑发育或组织损伤和修复的图谱。 ******拟议的计划重点是通过各种 MRI 技术研究 OD 及其潜在起源。我们的具体目标是： ******1。研究 R2* 松弛的 OD 与通过吸入气体混合物调节的静脉血氧合有何关系。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* 的方向依赖性。获取不同静脉血氧合程度的 R2* 图将使我们能够更详细地研究这些影响。 ******2.旨在研究白质 (WM) 方向如何影响通过基于造影剂的灌注成像获得的脑血流量和血容量图。我们将分析通过梯度回波和自旋回波扫描获取的灌注图，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.研究髓磷脂水图如何依赖于 WM 纤维方向（体内和离体）。 ******4。研究出生后最初几个月 R2* 松弛的 OD 如何演变。 ******由于灌注髓磷脂水和血液氧合成像被广泛使用，因此了解它们的局限性至关重要。此外，角度解析分析可以检测传统分析可能失败的脑组织变化。

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.