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. 2021 Aug;41(8):1899-1911.
doi: 10.1177/0271678X20982382. Epub 2021 Jan 14.

Regional and depth-dependence of cortical blood-flow assessed with high-resolution Arterial Spin Labeling (ASL)

Manuel Taso  1 , Fanny Munsch  1 , Li Zhao  2 , David C Alsop  1
Affiliations

Regional and depth-dependence of cortical blood-flow assessed with high-resolution Arterial Spin Labeling (ASL)

Manuel Taso et al. J Cereb Blood Flow Metab. 2021 Aug.

Abstract

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 T1 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)3 whole brain ASL data in a cohort of 10 volunteers at 3T, along with T1 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<10-5). ASL signal was higher towards the pial surface but correction for the shorter T1 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 T1 in the cortex complicates interpretation of depth-dependent ASL signal and may have implications for the accurate CBF quantification at lower resolutions.

Keywords: ASL; cerebral blood-flow; cortical perfusion; perfusion; surface-based analysis.

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Conflict of interest statement

Declaration of conflicting interests: The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: David C. Alsop is an inventor on patents related to the pseudo-continuous ASL method used in the current work. Consequently, he receives post-market royalties through his institution from GE Healthcare, Siemens Healthineers, Philips Healthcare, Hitachi Medical and Animage LLC. He additionally receives research support from GE Healthcare.

Figures

Figure 1.
Figure 1.
Example of (a) T1-weighted, (b) T1 map, (c) T2-FLAIR and (d) high-resolution 1.6mm isotropic ASL perfusion-weighted data.
Figure 2.
Figure 2.
Integrated and mid-distance sampled CBF, T1 and ATT projected on an inflated pial surface of the left hemisphere
Figure 3.
Figure 3.
Group Z-score maps showing CBF regional variation.
Figure 4.
Figure 4.
Uncorrected, as well as T1/ATT, T1 only and ATT-only corrected CBF sampled at mid-distance in the cortex (left-hemisphere). A relative color scale is shown because of different CBF values depending on which correction is used.
Figure 5.
Figure 5.
depth-dependence of cortical blood-flow before and after T1/ATT correction as well as T1, averaged across cortical ROIs (a) and in the precentral gyrus (b). The S/M/D marks represent grouping into superficial, middle and deep cortical layers.
See this image and copyright information in PMC

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