Abstract
The ability to evaluate the cerebral microvascular structure and function is crucial for investigating pathological processes in brain disorders. Previous angiographic methods based on blood oxygen level-dependent (BOLD) contrast offer appropriate visualization of the cerebral vasculature, but these methods remain to be optimized in order to extract more comprehensive information. This study aimed to integrate the advantages of BOLD MRI in both structural and functional vascular assessments. The BOLD contrast was manipulated by a carbogen challenge, and signal changes in gradient-echo images were computed to generate ΔR2* maps. Simultaneously, a functional index representing the regional cerebral blood volume was derived by normalizing the ΔR2* values of a given region to those of vein-filled voxels of the sinus. This method is named 3D gas ΔR2*-mMRA (microscopic MRA). The advantages of using 3D gas ΔR2*-mMRA to observe the microvasculature include the ability to distinguish air–tissue interfaces, a high vessel-to-tissue contrast, and not being affected by damage to the blood–brain barrier. A stroke model was used to demonstrate the ability of 3D gas ΔR2*-mMRA to provide information about poststroke revascularization at 3 days after reperfusion. However, this technique has some limitations that cannot be overcome and hence should be considered when it is applied, such as magnifying vessel sizes and predominantly revealing venous vessels.
Highlights
Abnormal structure and function of cerebral microvessels, including arterioles, venules, and capillaries, are pathological features that have been increasingly recognized in brain disorders [1]
The Choice of Optimal blood oxygen level-dependent (BOLD) Contrast by Gas Challenges The 3D high-resolution T2*-weighted images (T2*WIs) acquired during the inhalation of air, 100% oxygen, or carbogen exhibited different BOLD contrasts
Use of DR2* Maps to Reconstruct 3D gas DR2*-mMRA The 3D high-resolution T2*WIs acquired during the inhalation of air followed by carbogen are shown in Figure 2A and 2B, respectively
Summary
Abnormal structure and function of cerebral microvessels, including arterioles, venules, and capillaries, are pathological features that have been increasingly recognized in brain disorders [1]. 3D DR2-mMRA has been successfully used to detect arterioles and venules and obtain the microvascular cerebral blood volume (CBV), the application of contrast agents in MR angiography was found to have substantial limitations in a diseased status, such as in the presence of damage to the blood– brain barrier (BBB), which is a common pathological sign in many brain diseases. Such damage tends to result in contrast agent extravasating via the leaky BBB, which causes inaccurate visualization and estimation of the vasculature [9,10,11]. The use of iron-based contrast agents is problematic due to their availability, cost, and safety [12]
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