Multi-echo investigations of positive and negative CBF and concomitant BOLD changes

Devi, Ratnamanjuri; Lepsien, Jöran; Lorenz, Kathrin; Schlumm, Torsten; Mildner, Toralf; Möller, Harald E.

doi:10.1016/j.neuroimage.2022.119661

Cited by 4 publications

(1 citation statement)

References 108 publications

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“…Compared to single-echo acquisition, multi-echo (ME) is a fascinating approach that can address various goals in one acquisition, including sensitivity/SNR improvement and quantification of T 2 * relaxation time for clinical and basic neuroscience research. The ME scheme has been demonstrated with robust performance in various applications, including in a line-scanning fMRI with high spatiotemporal resolutions [16], in a combined gradientand spin-echo acquisition for simultaneous quantify T 2 * and T 2 relaxation time quantification [17], and in blood flow measurements to quantify T 2 * relaxation time [18]. Recently, a deep learning model was proposed for end-to-end parametric mapping for an overlapped multi-echo sequence [19].…”

Section: Introductionmentioning

confidence: 99%

Improved Resting-State Functional MRI Using Multi-Echo Echo-Planar Imaging on a Compact 3T MRI Scanner with High-Performance Gradients

Kang

et al. 2023

Sensors

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In blood-oxygen-level-dependent (BOLD)-based resting-state functional (RS-fMRI) studies, usage of multi-echo echo-planar-imaging (ME-EPI) is limited due to unacceptable late echo times when high spatial resolution is used. Equipped with high-performance gradients, the compact 3T MRI system (C3T) enables a three-echo whole-brain ME-EPI protocol with smaller than 2.5 mm isotropic voxel and shorter than 1 s repetition time, as required in landmark fMRI studies. The performance of the ME-EPI was comprehensively evaluated with signal variance reduction and region-of-interest-, seed- and independent-component-analysis-based functional connectivity analyses and compared with a counterpart of single-echo EPI with the shortest TR possible. Through the multi-echo combination, the thermal noise level is reduced. Functional connectivity, as well as signal intensity, are recovered in the medial orbital sulcus and anterior transverse collateral sulcus in ME-EPI. It is demonstrated that ME-EPI provides superior sensitivity and accuracy for detecting functional connectivity and/or brain networks in comparison with single-echo EPI. In conclusion, the high-performance gradient enabled high-spatial-temporal resolution ME-EPI would be the method of choice for RS-fMRI study on the C3T.

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Section: Introductionmentioning

confidence: 99%

Improved Resting-State Functional MRI Using Multi-Echo Echo-Planar Imaging on a Compact 3T MRI Scanner with High-Performance Gradients

Kang

et al. 2023

Sensors

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Two distinct modes of hemodynamic responses across the human cortex

Epp,

Castrillón,

Yuan

et al. 2023

Preprint

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Functional magnetic resonance imaging (fMRI) detects changes in brain activity by measuring fluctuations in blood oxygenation. While fMRI assumes a fixed relationship between changes in cerebral blood flow (CBF) and metabolic activity, its uniform application across the human cortex lacks complete validation. We used quantitative fMRI together with blood oxygenation level-dependent (BOLD) fMRI to assess oxygen metabolism against both positive and negative BOLD signal changes. We found a surprising mismatch between changes in oxygen consumption and the direction of BOLD signal changes (ΔBOLD) in 14-33% of voxels with significant positive, and in 50-66% of voxels with significant negative ΔBOLD. This implies that a substantial number of voxels with negative ΔBOLD actually demonstrate increased metabolic activity, and vice versa. Contrary to the canonical hemodynamic response model, discordant voxels cover their oxygen demand predominantly via changes in the oxygen extraction fraction (ΔOEF) and not via ΔCBF. This coincides with a higher vascular density and a lower OEF during baseline that we identified in discordant voxels. In summary, we identified a second type of hemodynamic response mechanism for regulating oxygen supply in the human brain. Our results suggest that the classical interpretation of positive and negative BOLD signal changes in terms of increased or decreased neural activity may be too simplistic and we recommend incorporating quantitative MRI or additional CBF measurements for a more accurate assessment of neuronal activity.

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A comparative analysis of the sensitivity and BOLD contamination of the VASO response at 3 Tesla: ME-DEPICTING vs. ME-EPI readouts

Devi,

Lepsien,

Mildner

et al. 2024

Imaging Neuroscience

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‘Non-BOLD fMRI’ data acquired at non-zero echo time (TE) suffer from contamination by the Blood Oxygenation Level Dependent (BOLD) signal due to the unavoidable signal decay caused by transverse relaxation. This contamination further reduces their already low inherent functional sensitivities and makes their correction essential. The Slice-Saturation Slab-Inversion (SS-SI) VASO, for instance, cancels out BOLD contributions from Vascular Space Occupancy (VASO) data, reflecting cerebral blood volume (CBV) changes, via a dynamic division approach. Alternatively, multi-echo (ME) data provide the possibility of extrapolating to TE=0. Acquisitions at very short TE would minimize the need for such corrections. The center-out EPI variant (“DEPICTING”) is one such readout which allows for short TE. The ME 2D DEPICTING was compared here against a traditional ME 2D EPI for its sensitivity to functional changes in the VASO signal. The two BOLD-correction schemes were also evaluated. Clear differences in functional sensitivity were observed for the uncorrected VASO data obtained from the first echo, TE1, of the two readouts. VASO data corrected by ME extrapolation were, however, found to be almost identical in their sensitivity for detecting CBV changes for both readouts. An excessively high increase in VASO signal sensitivity observed with the dynamic division correction for both readouts revealed a near-perfect linear dependence on TE of VASO signal changes. This could be attributed to the substantial intravascular BOLD contributions at 3 T. In the present data, extravascular ΔR2* fraction was found to be around ~50-60%. ME extrapolation is hence recommended to avoid overestimation of functional CBV changes at commonly used TEs.

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Multi-echo investigations of positive and negative CBF and concomitant BOLD changes

Cited by 4 publications

References 108 publications

Improved Resting-State Functional MRI Using Multi-Echo Echo-Planar Imaging on a Compact 3T MRI Scanner with High-Performance Gradients

Improved Resting-State Functional MRI Using Multi-Echo Echo-Planar Imaging on a Compact 3T MRI Scanner with High-Performance Gradients

Two distinct modes of hemodynamic responses across the human cortex

A comparative analysis of the sensitivity and BOLD contamination of the VASO response at 3 Tesla: ME-DEPICTING vs. ME-EPI readouts

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