Hi,
I have downloaded and unpacked HCP500_Parcellation_Timeseries_Netmats data.
My question is about group ICA spatial maps, specifically, about
melodic_IC.dscalar.nii and melodic_IC_ftb.dlabel.nii files in the groupICA*
subdirectories. There is a very short description of these files in the
accompanying PDF file:
melodic_IC.dscalar.nii ICA spatial maps (unthresholded
Zstats); one "timepoint" per map. Grayordinates
melodic_IC_ftb.dlabel.nii Summary "find the biggest" labels
image for all ICA spatial maps. Grayordinates
I have loaded these files generated for 25-dimensional group-ICA to wb_view
with corresponding Q1-Q6_R440_midthikness surface files for their
inspection.
1. I can appreciate Zstats maps provided for each IC by
melodic_IC.dscalar.nii. How were exactly these Zstats computed? Are these
regular Z-scores obtained by subtracting the vertex/voxel-wise mean and
dividing by the standard deviation, or something else?
2. When I click on the map and Information Window pops up, it shows
two SCALAR values for the selected vertex. For example:
VERTEX CortexLeft: 28165
ANATOMICAL XYZ: -6.28827, 59.2204, -0.919904
CIFTI SCALARS melodic_IC.dscalar.nii: 0.935668 -0.20834
What do these two numbers 0.935668 and -0.20834 actually mean? I though
there should be just one number corresponding to the Zstat of the vertex.
3. It appears that melodic_IC_ftb.dlabel.nii provides a hard
non-overlapping parcellation and labels each parcel (which could consist of
several spatially separated regions) by a color. The number of parcels
corresponds to the ICA dimension, 25 in this case. How is this parcellation
obtained? How is the set of spatially continuous/diffusive maps of
individual ICs give rise to this parcellation with sharp non-overlapping
borders and without any gaps between the neighboring parcels?
Thank you very much for your help.
Bagrat
Bagrat Amirikian, Ph.D.
Department of Neuroscience
University of Minnesota Medical School
Brain Sciences Center
Minneapolis Veterans Affairs Health Care System
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