Combined fMRI and DTI of the human low level visual cortex I. Abstract We study the anatomical...
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Transcript of Combined fMRI and DTI of the human low level visual cortex I. Abstract We study the anatomical...
Combined fMRI and DTI of the human low level visual cortex
I. AbstractWe study the anatomical connectivity network in the human low-level visual cortex using in vivo Magnetic Resonance Imaging techniques.
8 different visual areas were functionally mapped in each hemisphere of 4 subjects, and the white matter
fibers network among them was then investigated using DTI. Various intra and inter-hemispheric
connections were found, globally supporting the ventral/dorsal streams segregation.
Keywords: fMRI, DTI, visual areas, retinotopy, functional mapping, Riemannian geometry, fiber tracking
N. Wotawa†, C. Lenglet†, M. Roth*, B. Nazarian*, J.-L. Anton*, R. Majhoub*, R. Deriche†, O. Faugeras†
(†) I.N.R.I.A., 2004 route des Lucioles, 06902 Sophia-Antipolis, France(*) Centre IRMf de Marseille, CHU Timone, 13385 Marseille, France Odyssée Lab
V. Results and Conclusion
III. ROIs definition from fMRI• Two different criteria to define various low-level visual areas: retinotopy and functional selectivity
• Visual stimuli: 300x300 pixels video, 20.9°x20.9° visual angle, 72Hz refresh rate
• Attention and fixation controlled through a discrimination task at the fixation cross (normal: 0.5°, test: 0.77°)
• Preprocessings:
Segmented areas: V1, V2v-V2d, V3v-V3d, V3A, V4.
Volumetric ROIs computed through a 3mm “retro-projection” along the GM/WM interface normals
80°, 8 rotations
4 rotations
2/ Functional mapping of hMT+ (10mns)
• hMT+ complex: visual motion sensitive area, presumably human homologue of MT/V5 + MST (+ FST)
• Classical block design: RDP in coherent radial motion (7.53 deg.s-1, 2Hz alternating) VS flicker or static
• 2 x 5mns run, 3x8 blocks of ~17secs each
• hMT+ volumetric ROIs extracted with SPM99 - Marsbar Toolbox
II. Data acquisition• 3T MEDSPEC 30/80 AVANCE (Bruker) at the Centre IRMf de Marseille, quadrature bird-cage head coil
• Anatomical image: T1-weighted MPRAGE, TR=25msec, TE=5ms, FOV 256x230x180mm 3,
voxel size = 1x0.75x1.22mm3, 15mns
• fMRI: 30 pseudo-coronal slices, TR=2.111sec, TE=35ms, voxel size=2x2x2mm 3
• DTI: 12 directions, repeated 8 times, b=1000 s.mm -2, =38.5ms, =21.6ms, TR=10000ms, TE=83ms.
voxel size = 2x2x2mm3, 20mns
•
Investigation of the low level visual cortex areas considering 3 different characterization criteria within
<1.5h of scans for the whole experiment
Intra and Inter-hemispheric connexions were found in all subjects
Good inter-subjects reproducibility (4 subjects)
Our data support the dorsal (V1, V3A, hMT+) and v entral (V1, V2, V3, V4) streams
1462 W-PM Human Brain Mapping, Toronto, Ontario, Canada, June 12-16, 2005
1/ Retinotopic mapping of occipital areas (25mns) Standard procedure by phase-encoded stimulation of the visual field
P-uncorr.
10-2
10-10
0
1000
Centre IRMf
Results of the fiber tracking with every white matter voxels taken as a seed from a single left hMT+
voxel. Dark values correspond to low mean along the fibers, indicating a strong connectivity index.
White matter segmentation (Brainvisa and Absolut).Each white matter voxel is considered as a seed for the
fiber tracking algorithm.
IV. DTI Fiber Tracking & Connections Likelihood
Basic idea: DTI fiber tracking and estimation of an index of connectivity for each fiber are conducted as follows. Diffusion tensor are used as a metric to first compute geodesic distances and then the shortest paths between the ROIs extracted from fMRI. A measure of likelihood for each computed fiber is then derived by looking at the minima of the distance function Euclidean gradient norm.
Estimation of diffusion tensors by a robust gradient descent algorithm (see poster 736 T-
PM)
ROI
Distance function computation:
Statistics of along two distinct fibers toward the same target. Fibers with high
variance (red) are discarded
3D rendering of geodesics with best statistical properties of with left hMT+ (red) as a target.Fiber tracts strongly connect contralateral hMT+ (green) and contralateral as well as ipsilateral (blue) V1 area.
Synthetic example of distance function
Real dataset distance function from a corpus callosum voxel over an axial slice
motion correction (INRIAlign Sofware) cortical surface-based anisotropic smoothing, FWHM=3mm (Odyssee Lab. software) MNI template normalization (SPM2)
Fiber with low confidenceMean = 1815Standard deviation = 1160
Fiber with high confidenceMean = 1020Standard deviation = 180