There is an urgent need for better detection and understanding of vascular abnormalities at the micro-level, where critical vascular nourishment and cellular metabolic changes occur. This is especially the case for structures such as the midbrain where both the feeding and draining vessels are quite small. Being able to monitor and diagnose vascular changes earlier will aid in better understanding the etiology of the disease and in the development of therapeutics. In this work, thirteen healthy volunteers were scanned with a dual echo susceptibility weighted imaging (SWI) sequence, with a resolution of 0.22×0.44×1mm3. Ultra-small superparamagnetic iron oxides (USPIO) were used to induce an increase in susceptibility in both arteries and veins. Although the increased vascular susceptibility enhances the visibility of small subvoxel vessels, the accompanying strong signal loss of the large vessels deteriorates the local tissue contrast. To overcome this problem, the SWI data were acquired at different time points during a gradual administration (final concentration = 4mg/kg) of the USPIO agent, Ferumoxytol, and the data was processed to combine the SWI data dynamically, in order to see through these blooming artifacts. The major vessels and their tributaries (such as the collicular artery, peduncular artery, peduncular vein and the lateral mesencephalic vein) were identified on the combined SWI data using arterio-venous maps. Dynamically combined SWI data was then compared with previous histological work to validate that this protocol was able to detect small vessels on the order of 50μm to 100μm. A complex division-based phase unwrapping was also employed to improve the quality of quantitative susceptibility maps by reducing the artifacts due to aliased voxels at the vessel boundaries. The smallest detectable vessel size was then evaluated by revisiting numerical simulations, using estimated true susceptibilities for the basal vein and the posterior cerebral artery in the presence of Ferumoxytol. These simulations suggest that vessels as small as 50μm should be visible with the maximum dose of 4mg/kg.

中文翻译：

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使用 USPIO 增强 MRI 对中脑进行亚体素血管成像

迫切需要在微观层面更好地检测和了解血管异常，其中发生关键的血管营养和细胞代谢变化。对于像中脑这样的进给和引流血管都非常小的结构来说尤其如此。能够更早地监测和诊断血管变化将有助于更好地了解疾病的病因和治疗方法的开发。在这项工作中，对 13 名健康志愿者进行了双回波敏感性加权成像 (SWI) 序列扫描，分辨率为 0.22×0.44×1mm3。超小型超顺磁性氧化铁 (USPIO) 用于诱导动脉和静脉的易感性增加。虽然增加的血管易感性增强了小亚体素血管的可见性，伴随的大血管的强信号损失使局部组织对比度恶化。为了克服这个问题，在USPIO药剂Ferumoxytol的逐渐给药（最终浓度= 4mg / kg）期间的不同时间点获取SWI数据，并处理数据以动态组合SWI数据，以便看透这些绽放的神器。使用动静脉图在组合 SWI 数据上识别主要血管及其支流（如丘动脉、蒂动脉、蒂静脉和中脑外侧静脉）。然后将动态组合的 SWI 数据与以前的组织学工作进行比较，以验证该协议能够检测到 50μm 到 100μm 的小血管。还采用了基于复杂划分的相位展开，通过减少由于血管边界处的混叠体素造成的伪影来提高定量磁敏度图的质量。然后通过重新访问数值模拟评估最小的可检测血管尺寸，使用在 Ferumoxytol 存在下估计的基底静脉和大脑后动脉的真实敏感性。这些模拟表明，在最大剂量为 4mg/kg 的情况下，小至 50μm 的血管应该是可见的。