Laminar fMRI using T2-prepared multi-echo FLASH
Functional magnetic resonance imaging (fMRI) using blood oxygenation level dependent (BOLD) contrast at a sub-millimeter scale is a promising technique to probe neural activity at the level of cortical layers. While gradient echo (GRE) BOLD sequences exhibit the highest sensitivity, their signal is...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Elsevier
2021-08-01
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| Series: | NeuroImage |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S1053811921004407 |
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| author | Viktor Pfaffenrot Maximilian N. Voelker Sriranga Kashyap Peter J. Koopmans |
| author_facet | Viktor Pfaffenrot Maximilian N. Voelker Sriranga Kashyap Peter J. Koopmans |
| author_sort | Viktor Pfaffenrot |
| collection | DOAJ |
| description | Functional magnetic resonance imaging (fMRI) using blood oxygenation level dependent (BOLD) contrast at a sub-millimeter scale is a promising technique to probe neural activity at the level of cortical layers. While gradient echo (GRE) BOLD sequences exhibit the highest sensitivity, their signal is confounded by unspecific extravascular (EV) and intravascular (IV) effects of large intracortical ascending veins and pial veins leading to a downstream blurring effect of local signal changes. In contrast, spin echo (SE) fMRI promises higher specificity towards signal changes near the microvascular compartment. However, the T2-weighted signal is typically sampled with a gradient echo readout imposing additional T2’-weighting.In this work, we used a T2-prepared (T2-prep) sequence with short GRE readouts to investigate its capability to acquire laminar fMRI data during a visual task in humans at 7 T. By varying the T2-prep echo time (TEprep) and acquiring multiple gradient echoes (TEGRE) per excitation, we studied the specificity of the sequence and the influence of possible confounding contributions to the shape of laminar fMRI profiles. By fitting and extrapolating the multi-echo GRE data to a TEGRE = 0 ms condition, we show for the first time laminar profiles free of T2’-pollution, confined to gray matter. This finding is independent of TEprep, except for the shortest one (31 ms) where hints of a remaining intravascular component can be seen. For TEGRE > 0 ms a prominent peak at the pial surface is observed that increases with longer TEGRE and dominates the shape of the profiles independent of the amount of T2-weighting. Simulations show that the peak at the pial surface is a result of static EV dephasing around pial vessels in CSF visible in GM due to partial voluming. Additionally, another, weaker, static dephasing effect is observed throughout all layers of the cortex, which is particularly obvious in the data with shortest T2-prep echo time. Our simulations show that this cannot be explained by intravascular dephasing but that it is likely caused by extravascular effects of the intracortical and pial veins. We conclude that even for TEGRE as short as 2.3 ms, the T2’-weighting added to the T2-weighting is enough to dramatically affect the laminar specificity of the BOLD signal change. However, the bulk of this corruption stems from CSF partial volume effects which can in principle be addressed by increasing the spatial resolution of the acquisition. |
| first_indexed | 2024-12-21T21:03:01Z |
| format | Article |
| id | doaj.art-71ea01ac46d147579460754b499c54af |
| institution | Directory Open Access Journal |
| issn | 1095-9572 |
| language | English |
| last_indexed | 2024-12-21T21:03:01Z |
| publishDate | 2021-08-01 |
| publisher | Elsevier |
| record_format | Article |
| series | NeuroImage |
| spelling | doaj.art-71ea01ac46d147579460754b499c54af2022-12-21T18:50:23ZengElsevierNeuroImage1095-95722021-08-01236118163Laminar fMRI using T2-prepared multi-echo FLASHViktor Pfaffenrot0Maximilian N. Voelker1Sriranga Kashyap2Peter J. Koopmans3Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, 45141 Essen, Germany; High-Field and Hybrid MR Imaging, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany; Corresponding author at: Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Kokereiallee 7, 45141 Essen, Germany.Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, 45141 Essen, Germany; High-Field and Hybrid MR Imaging, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, GermanyDepartment of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, 6229 Maastricht, NetherlandsErwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, 45141 Essen, Germany; High-Field and Hybrid MR Imaging, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, GermanyFunctional magnetic resonance imaging (fMRI) using blood oxygenation level dependent (BOLD) contrast at a sub-millimeter scale is a promising technique to probe neural activity at the level of cortical layers. While gradient echo (GRE) BOLD sequences exhibit the highest sensitivity, their signal is confounded by unspecific extravascular (EV) and intravascular (IV) effects of large intracortical ascending veins and pial veins leading to a downstream blurring effect of local signal changes. In contrast, spin echo (SE) fMRI promises higher specificity towards signal changes near the microvascular compartment. However, the T2-weighted signal is typically sampled with a gradient echo readout imposing additional T2’-weighting.In this work, we used a T2-prepared (T2-prep) sequence with short GRE readouts to investigate its capability to acquire laminar fMRI data during a visual task in humans at 7 T. By varying the T2-prep echo time (TEprep) and acquiring multiple gradient echoes (TEGRE) per excitation, we studied the specificity of the sequence and the influence of possible confounding contributions to the shape of laminar fMRI profiles. By fitting and extrapolating the multi-echo GRE data to a TEGRE = 0 ms condition, we show for the first time laminar profiles free of T2’-pollution, confined to gray matter. This finding is independent of TEprep, except for the shortest one (31 ms) where hints of a remaining intravascular component can be seen. For TEGRE > 0 ms a prominent peak at the pial surface is observed that increases with longer TEGRE and dominates the shape of the profiles independent of the amount of T2-weighting. Simulations show that the peak at the pial surface is a result of static EV dephasing around pial vessels in CSF visible in GM due to partial voluming. Additionally, another, weaker, static dephasing effect is observed throughout all layers of the cortex, which is particularly obvious in the data with shortest T2-prep echo time. Our simulations show that this cannot be explained by intravascular dephasing but that it is likely caused by extravascular effects of the intracortical and pial veins. We conclude that even for TEGRE as short as 2.3 ms, the T2’-weighting added to the T2-weighting is enough to dramatically affect the laminar specificity of the BOLD signal change. However, the bulk of this corruption stems from CSF partial volume effects which can in principle be addressed by increasing the spatial resolution of the acquisition.http://www.sciencedirect.com/science/article/pii/S1053811921004407T2-weightingLayer fMRIBOLD contrast mechanisms |
| spellingShingle | Viktor Pfaffenrot Maximilian N. Voelker Sriranga Kashyap Peter J. Koopmans Laminar fMRI using T2-prepared multi-echo FLASH NeuroImage T2-weighting Layer fMRI BOLD contrast mechanisms |
| title | Laminar fMRI using T2-prepared multi-echo FLASH |
| title_full | Laminar fMRI using T2-prepared multi-echo FLASH |
| title_fullStr | Laminar fMRI using T2-prepared multi-echo FLASH |
| title_full_unstemmed | Laminar fMRI using T2-prepared multi-echo FLASH |
| title_short | Laminar fMRI using T2-prepared multi-echo FLASH |
| title_sort | laminar fmri using t2 prepared multi echo flash |
| topic | T2-weighting Layer fMRI BOLD contrast mechanisms |
| url | http://www.sciencedirect.com/science/article/pii/S1053811921004407 |
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