Re: [Freesurfer] Relation between Segmentation Volumes and number of pixels in Aseg+aparc.mgz

more exact than what?

On 4/25/17 2:07 PM, Gamaliz wrote:

Is there any way to generate a file which is more exact? Or perhaps, is that file already there?

On Tue, Apr 25, 2017 at 2:04 PM, Douglas Greve <greve@nmr.mgh.harvard.edu mailto:greve@nmr.mgh.harvard.edu> wrote:

The aseg.stats is generated with partial volume estimation


On 4/25/17 12:40 PM, Gamaliz wrote:

...

I wrote an algorithm which uses the number of pixels per region
in the aseg+aparc.mgz file. As this file has 1x1x1mm3 I was
expecting the number of pixels to match very closely the value of
the volume; as each pixel represents a 1 mm3 cube.(I did the same
for cortical volume and got a similar result, with an even larger
discrepancy).

The aseg.stats file lists the nVoxel value, and it is basically
the volume rounded up.
here are some sample values for subcortical regions:

Left-Lateral-Ventricle Volume (mm3): 7829.8
Left-Lateral-Ventricle (number of Pixels in aseg+aparc.mgz): 7396
Left-Inf-Lat-Vent Volume (mm3):594
Left-Inf-Lat-Vent(number of Pixels in aseg+aparc.mgz):569
Left-Cerebellum-White-Matter Volume (mm3):12668
Left-Cerebellum-White-Matter(number of Pixels in
aseg+aparc.mgz):12203
Left-Cerebellum-Cortex Volume (mm3):44113.2
Left-Cerebellum-Cortex(number of Pixels in aseg+aparc.mgz):43804
Left-Thalamus-Proper Volume (mm3):5752.8
Left-Thalamus-Proper(number of Pixels in aseg+aparc.mgz):5899

Pretty much the values are close to the volume, but different
enough to be significant. I wonder why this discrepancy.


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