Got it. 
Thanks for the prompt answer! 
By the way, I tried mri_segstats with --accumulate flag, but it says option '--accumulate' is unknown. 
I don't seem to find it when I looked up mri_segstas --help either. 
 


On Tue, Jun 11, 2013 at 5:05 PM, Douglas N Greve <greve@nmr.mgh.harvard.edu> wrote:

Right, so in this case, the "NVoxels" column is the number of vertices, the "Mean" column is the average surface area of the vertices in the mask. You can force it to compute the total surface area by adding the --accumulate flag. Or you can multiple the mean by the number of vertices.
doug



On 06/11/2013 04:55 PM, Glen Lee wrote:
Hi Doug --
I copied and pasted the summary file below.
It looks like mask.mgh was treated as volumetric image.
Also I'm not sure how to interpret TableCol.



# Title Segmentation Statistics
#
# generating_program mri_segstats
# cvs_version $Id: mri_segstats.c,v 1.75.2.2 2011/04/27 22:18:58 nicks Exp $
# cmdline mri_segstats --seg mask.mgh --id 1 --i /fMRI/2D/freesurfer/fsaverage_sym/surf/lh.area --sum sum.dat
# sysname  Linux
# hostname rage.uphs.upenn.edu <http://rage.uphs.upenn.edu>

# machine  x86_64
# user     gel
# anatomy_type volume
#
# SegVolFile mask.mgh
# SegVolFileTimeStamp  2013/06/05 14:50:24
# InVolFile  /fMRI/2D/freesurfer/fsaverage_sym/surf/lh.area
# InVolFileTimeStamp  2013/05/22 16:49:43
# InVolFrame 0
# Only reporting non-empty segmentations
# VoxelVolume_mm3 1
# TableCol  1 ColHeader Index
# TableCol  1 FieldName Index
# TableCol  1 Units     NA
# TableCol  2 ColHeader SegId
# TableCol  2 FieldName Segmentation Id
# TableCol  2 Units     NA
# TableCol  3 ColHeader NVoxels
# TableCol  3 FieldName Number of Voxels
# TableCol  3 Units     unitless
# TableCol  4 ColHeader Volume_mm3
# TableCol  4 FieldName Volume
# TableCol  4 Units     mm^3
# TableCol  5 ColHeader Mean
# TableCol  5 FieldName Intensity Mean
# TableCol  5 Units     unknown
# TableCol  6 ColHeader StdDev
# TableCol  6 FieldName Itensity StdDev
# TableCol  6 Units     unknown
# TableCol  7 ColHeader Min
# TableCol  7 FieldName Intensity Min
# TableCol  7 Units     unknown
# TableCol  8 ColHeader Max
# TableCol  8 FieldName Intensity Max
# TableCol  8 Units     unknown
# TableCol  9 ColHeader Range
# TableCol  9 FieldName Intensity Range
# TableCol  9 Units     unknown
# NRows 1
# NTableCols 9
# ColHeaders  Index SegId NVoxels Volume_mm3 StructName Mean StdDev Min Max Range
  1   1     81837    81837.0  Seg0001     0.3836     0.1111     0.1297     1.1861     1.0563


On Tue, Jun 11, 2013 at 11:44 AM, Douglas N Greve <greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu>> wrote:

    Did you look in the summary file? If you have questions about
    that, can you send it?
    doug


    On 06/11/2013 11:34 AM, Glen Lee wrote:

        mri_segstats --seg mask.mgh --id 1 --i
        /fMRI/2D/freesurfer/fsaverage_sym/surf/lh.area --sum sum.dat


        On Tue, Jun 11, 2013 at 10:41 AM, Douglas Greve
        <greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu>
        <mailto:greve@nmr.mgh.harvard.edu

        <mailto:greve@nmr.mgh.harvard.edu>>> wrote:

            what is your full command line?


            On 6/11/13 10:04 AM, Glen Lee wrote:

                thanks Doug.
                it worked and I got the following result on which I have
                clarifying questions:

                --------------
                Voxel Volume is 1 mm^3
                Generating list of segmentation ids
                Found   1 segmentations
                Computing statistics for each segmentation
                  0 1 81837 81837 <tel:1%2081837%20%2081837>

            <tel:1%20%C2%A0%2081837%20%C2%A081837>

                ----------------

                1) I'm assuming that voxel here refers to vertex since I'm
                submitting the surface data.

                2) what does 'found 1 segmentations mean'?

                3) the dimension is 81837mm^2, correct?




                On Tue, Jun 11, 2013 at 12:31 AM, Douglas Greve
                <greve@nmr.mgh.harvard.edu
            <mailto:greve@nmr.mgh.harvard.edu>
            <mailto:greve@nmr.mgh.harvard.edu

            <mailto:greve@nmr.mgh.harvard.edu>>> wrote:

                    It's --sum for this, not --o
                    doug


                    On 6/10/13 4:44 PM, Glen Lee wrote:

                        Thanks Doug!

                        I just tried, but I got an error:
                        mri_segstats --seg mask.mgh --id 1 --i
                        /fMRI/2D/freesurfer/fsaverage_sym/surf/lh.area
                --o sum.dat
                        ERROR: Option --o unknown

                        I don't see --o option when I looked up
                mri_segstats --help
                        either. FYI, I'm using v5.1.
                        Any idea?



                        On Mon, Jun 10, 2013 at 3:39 PM, Douglas N Greve
                        <greve@nmr.mgh.harvard.edu
                <mailto:greve@nmr.mgh.harvard.edu>
                        <mailto:greve@nmr.mgh.harvard.edu

                <mailto:greve@nmr.mgh.harvard.edu>>> wrote:


                            Hi Glen, you can use

                            mri_segstats --seg mask.mgh --id 1 --i
                            $SUBJECTS_DIR/fsaverage_sym/surf/lh.area
                --o sum.dat

                            doug


                            On 06/10/2013 03:17 PM, Glen Lee wrote:
                            > Dear freesurfer users
                            >
                            > I'm wondering if there is any way of
                figuring out the
                            surface size
                            > within a mask image (mask.mgh)
                            > which is generated after running a
                group-level GLM
                            analysis (2nd RFX)
                            > using mri_glmfit.
                            >
                            > As I'm thinking, this may be:
                            >   number of vertex by dimension of one
                vertex (1mm).
                            >
                            > But I could be wrong and let me know if
                anyone knows
                            the solution.
                            >
                            > -Glen
                            >
                            > fyi) the group analysis was performed in
                freesurfer
                            sym space.
                            >
                            >
                            >
                            >
                _______________________________________________
                            > Freesurfer mailing list
                            > Freesurfer@nmr.mgh.harvard.edu
                <mailto:Freesurfer@nmr.mgh.harvard.edu>
                            <mailto:Freesurfer@nmr.mgh.harvard.edu

                <mailto:Freesurfer@nmr.mgh.harvard.edu>>

                            >
                https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer

                            --
                            Douglas N. Greve, Ph.D.
                            MGH-NMR Center
                greve@nmr.mgh.harvard.edu
                <mailto:greve@nmr.mgh.harvard.edu>
                <mailto:greve@nmr.mgh.harvard.edu

                <mailto:greve@nmr.mgh.harvard.edu>>
                            Phone Number: 617-724-2358
                <tel:617-724-2358> <tel:617-724-2358 <tel:617-724-2358>>
                            Fax: 617-726-7422 <tel:617-726-7422>
                <tel:617-726-7422 <tel:617-726-7422>>


                            Bugs:
                surfer.nmr.mgh.harvard.edu/fswiki/BugReporting
                <http://surfer.nmr.mgh.harvard.edu/fswiki/BugReporting>
                                           <http://surfer.nmr.mgh.harvard.edu/fswiki/BugReporting>
                            FileDrop:
                https://gate.nmr.mgh.harvard.edu/filedrop2
                www.nmr.mgh.harvard.edu/facility/filedrop/index.html
                <http://www.nmr.mgh.harvard.edu/facility/filedrop/index.html>
                                           <http://www.nmr.mgh.harvard.edu/facility/filedrop/index.html>


                            Outgoing:
                ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/

                                           _______________________________________________
                            Freesurfer mailing list
                Freesurfer@nmr.mgh.harvard.edu
                <mailto:Freesurfer@nmr.mgh.harvard.edu>
                            <mailto:Freesurfer@nmr.mgh.harvard.edu

                <mailto:Freesurfer@nmr.mgh.harvard.edu>>

                https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer


                            The information in this e-mail is intended
                only for the
                            person to whom it is
                            addressed. If you believe this e-mail was
                sent to you in
                            error and the e-mail
                            contains patient information, please
                contact the
                            Partners Compliance HelpLine at
                http://www.partners.org/complianceline . If the e-mail
                            was sent to you in error
                            but does not contain patient information,
                please contact
                            the sender and properly
                            dispose of the e-mail.







    --     Douglas N. Greve, Ph.D.
    MGH-NMR Center