Department of Radiology, Wayne State University, Detroit, MI, USA.
Department of Radiology, Wayne State University, Detroit, MI, USA; Magnetic Resonance Innovations, Inc., Bingham Farms, MI, USA.
Neuroimage. 2020 Oct 15;220:117106. doi: 10.1016/j.neuroimage.2020.117106. Epub 2020 Jun 29.
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 × 1 mm at 3T. 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 = 4 mg/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 50 μm-100 μm. 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 50 μm should be visible with the maximum dose of 4 mg/kg.
目前迫切需要更好地检测和理解微观水平的血管异常，因为关键的血管营养和细胞代谢变化都发生在这个水平。对于中脑等结构，这种情况尤其如此，因为供血和引流血管都相当小。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，并开发治疗方法。在这项工作中，13 名健康志愿者在 3T 下使用双回波磁化率加权成像（SWI）序列进行扫描，分辨率为 0.22×0.44×1mm。超小超顺磁性氧化铁（USPIO）用于在动脉和静脉中引起磁化率增加。虽然增加的血管磁化率增强了亚像素小血管的可见性，但大血管的伴随强信号损失会降低局部组织对比度。为了克服这个问题，SWI 数据是在 USPIO 试剂（最终浓度为 4mg/kg）逐渐给药的不同时间点采集的，并对数据进行处理以动态组合 SWI 数据，以便穿透这些blooming 伪影。使用动静脉图谱，在组合的 SWI 数据上识别出主要血管及其分支（如丘脑血管、脚间动脉、脚间静脉和外侧中脑静脉）。然后将动态组合的 SWI 数据与之前的组织学工作进行比较，以验证该方案能够检测到 50-100μm 量级的小血管。还采用了基于复杂划分的相位解缠技术，通过减少血管边界处混叠体素引起的伪影，来提高定量磁化率图的质量。然后通过重新进行数值模拟，使用存在 Ferumoxytol 时基底静脉和大脑后动脉的估计真实磁化率来评估最小可检测血管尺寸。这些模拟表明，使用 4mg/kg 的最大剂量，应该可以看到 50μm 大小的血管。
