Neuroscience 2000 Abstract
| Presentation Number: | 550.12 |
|---|---|
| Abstract Title: | Human bold functional MRI at 4 and 7 tesla: evaluation of microvascular versus macrovascular contribution. |
| Authors: |
Kim, S. G.*1
; Cohen, E. R.1
; Merkle, H.1
; Adriany, G.1
; Andersen, P.1
; Ugurbil, K.1
; Duong, T. Q.1
1Center for Magnetic Resonance Research, University of Minnesota Medical School, MN |
| Primary Theme and Topics |
F. Sensory Systems - 79. Visual cortex: striate |
| Session: |
550. Visual cortex: striate--maps and imaging II Poster |
| Presentation Time: | Tuesday, November 7, 2000 4:00 PM-5:00 PM |
| Location: | Hall G-J |
| Keywords: | fMRI, BOLD, Blood Flow, CBF |
It has been shown that the blood oxygenation level dependent (BOLD) functional MRI signal at magnetic field strengths of ≤ 1.5T arises predominantly from large vessels, which can be quite distant from the sites of neuronal activity. To improve the spatial localization to the active tissues/capillaries, the use of high field magnets has been proposed. To test this hypothesis, we evaluated the microvascular versus the macrovascular contribution to the BOLD response at high fields (4 and 7T) following visual stimulation in humans. Diffusion-weighted BOLD fMRI was used to selectively attenuate the fast-moving (large-vessel) fMRI signals. Two acquisition schemes were used: a gradient-echo scheme which is sensitive to both large- and small-vessel BOLD effects and a spin-echo scheme which should mitigate large-vessel BOLD effects. A comparison was made between the two sets of results. Diffusion-weighted BOLD fMRI was performed on 24 normal humans with graded flow-crushing gradients (4-7 b values). The visual stimulus consisted of red LEDs flashing at 10 Hz. The gradient-echo EPI parameters were: TR=2s, and TE=80ms (4T) or 60ms (7T). The spin-echo EPI parameters were: TR=2s, and TE=60ms (4T) or 50ms (7T). BOLD sensitivity at 7T was qualitatively better than that at 4T, though differences in acquisition parameters and signal sources prevented a quantitative comparison. The spin-echo BOLD maps showed reduced large-vessel contribution compared with the gradient-echo BOLD maps. In marked contrast to the results of the 1.5T studies, the gradient-echo BOLD percent changes at both 4 and 7T showed negligible decreases with increasing flow-crushing gradients, suggesting a negligible intravascular, large-vessel contribution at high fields. These results are consistent with the hypothesis that high fields yield differential sensitivity toward microvascular relative to macrovascular BOLD responses. We concluded that the intravascular large-vessel contribution to the BOLD signal was markedly attenuated at high fields. In combination with flow-crushing gradients and/or a spin-echo acquisition scheme, significant improvement in spatial localization and specificity can be achieved.
Supported by NIH (RR08079, NS10930, NS38295, MH57180), Keck Fdn.
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2000 Neuroscience Meeting Planner. New Orleans, LA: Society for Neuroscience, 2000. Online.
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