Neuroscience 2000 Abstract
| Presentation Number: | 309.7 |
|---|---|
| Abstract Title: | Delay of fMRI response in blood vessels versus parenchyma. |
| Authors: |
Saad, Z. S.*1
; Lewis, J. W.2
; Ropella, K. M.1
; DeYoe, E. A.2
1Biomedical Eng., Marquette Univ., Milwaukee, WI 2Cell. Bio. & Anat., Med. Col. of Wisconsin, Milwaukee, WI |
| Primary Theme and Topics |
F. Sensory Systems - 79. Visual cortex: striate |
| Session: |
309. Visual cortex: striate--maps and imaging I Slide |
| Presentation Time: | Monday, November 6, 2000 2:30 PM-2:45 PM |
| Location: | Room 393 |
| Keywords: | Functional Imaging, Response Latency, Human Visual Cortex, Venous Blood Flow |
Empirical data from Functional Magnetic Resonance Imaging (FMRI) of human brain have revealed variations in response delay on the order of 10 seconds [1,2,3]. This relatively wide range of delays has been attributed to the delayed flow of blood through large veins draining the sites of neuronal activation [1,2]. This study examined the difference in response delays between large blood vessels and parenchyma using two independent, unbiased methods for classifying activated voxels as vessel- or parenchyma- related. FMRI images (BOLD EPI, 1.5 T. voxel size 3.75 × 3.75 ×4 mm) from 3 subjects were obtained during visual stimulation consisting of a checkered annulus centered on a gray fixation point alternating with fixation alone. High-resolution FMRI images (3T, voxel size 1.0×1.0 ×1.2 mm) were also obtained for one of the subjects. In the first classification method, we imaged blood vessels directly using 2D-TOF MRI capable of resolving blood vessels greater than 2 mm in diameter. Stimulus-activated voxels were classified as blood vessels if they overlapped with high intensity voxels in 2D-TOF images. In the second method, voxels were classified as blood vessels if they exhibited large signal changes in response to the stimulus [4]. Given the arbitrary threshold criteria for voxel classification, we examined delay differences across a range of thresholds. For each subject, the maximum significant delay difference between blood vessels and parenchyma was then determined. Across all subjects, image resolutions and classification methods, mean delays for blood vessels were only 1.5 s (range 0.7 to 2.4 s) longer than those for parenchyma (p <0.01). Moreover, long delays were obtained from both parenchyma and vessels, thereby indicating that response delay is not a sufficient criterion for identifying and rejecting FMRI signals arising from large blood vessels, as proposed previously [2]. [1] Lai et al. (93) MRM 30. [2] Lee et al. (95) MRM 33. [3] Saad et al. (95) proc. SMR95. [4] Ogawa et al. (93) Biophys J.. 64.
Supported by Whitaker Foundation, R. Bagozzi fellowship to K. Ropella, NIH grants EY10244, MH51358 to E. DeYoe.
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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