Division of MRI Research, Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
Diagnostic Imaging and Radiology, Children's National Hospital, Washington, DC, USA.
J Cereb Blood Flow Metab. 2021 Aug;41(8):1899-1911. doi: 10.1177/0271678X20982382. Epub 2021 Jan 14.
Methods for imaging of cerebral blood flow do not typically resolve the cortex and thus underestimate flow. However, recent work with high-resolution MRI has emphasized the regional and depth-dependent structural, functional and relaxation times variations within the cortex. Using high-resolution Arterial Spin Labeling (ASL) and T mapping acquisitions, we sought to probe the effects of spatial resolution and tissue heterogeneity on cortical cerebral blood flow (CBF) measurements with ASL. We acquired high-resolution (1.6mm) whole brain ASL data in a cohort of 10 volunteers at 3T, along with T and transit-time (ATT) mapping, followed by group cortical surface-based analysis using FreeSurfer of the different measured parameters. Fully resolved regional analysis showed higher than average mid-thickness CBF in primary motor areas (+15%,p<0.002), frontal regions (+17%,p<0.01) and auditory cortex, while occipital regions had lower average CBF (-20%,p<10). ASL signal was higher towards the pial surface but correction for the shorter T near the white matter surface reverses this gradient, at least when using the low-resolution ATT map. Similar to structural measures, fully-resolved ASL CBF measures show significant differences across cortical regions. Depth-dependent variation of T in the cortex complicates interpretation of depth-dependent ASL signal and may have implications for the accurate CBF quantification at lower resolutions.
方法学研究表明,脑血流成像通常无法解析皮质,因此会低估皮质的血流量。然而,最近应用高分辨率磁共振成像(MRI)的研究强调了皮质在结构、功能和弛豫时间方面存在区域性和深度依赖性的变化。我们使用高分辨率动脉自旋标记(ASL)和 T 映射采集技术,旨在探讨空间分辨率和组织异质性对 ASL 测量皮质脑血流量(CBF)的影响。我们在 3T 扫描仪上对 10 名志愿者进行了高分辨率(1.6mm)全脑 ASL 数据采集,同时采集了 T 和渡越时间(ATT)映射图,然后使用 FreeSurfer 对不同测量参数进行皮质表面的基于组的分析。完全解析的区域分析显示,初级运动区(+15%,p<0.002)、额区(+17%,p<0.01)和听觉皮层的中层 CBF 高于平均水平,而枕叶区的平均 CBF 较低(-20%,p<10)。ASL 信号在软脑膜表面较高,但由于白质表面附近 T 值较短,校正后会反转这种梯度,至少在使用低分辨率 ATT 图时是这样。与结构测量相似,完全解析的 ASL CBF 测量值在皮质区域之间显示出显著差异。皮质内 T 的深度依赖性变化使深度依赖性 ASL 信号的解释变得复杂,并且可能对较低分辨率下的准确 CBF 定量产生影响。