Just checked mris_euler_number, holes are calculated from euler number: holes = 1-eno/2

From: freesurfer-bounces@nmr.mgh.harvard.edu freesurfer-bounces@nmr.mgh.harvard.edu On Behalf Of Fischl, Bruce R.,PHD Sent: Thursday, February 1, 2024 10:27 AM To: Freesurfer support list freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] Euler number calculation from number of holes

Hi Melissa

mris_euler_number <surface>

writes out a bunch of stuff, including the Euler number:

mris_euler_number ~/links/subjects/bruce.dev/surf/lh.orig.nofix euler # = v-e+f = 2g-2: 154526 - 463668 + 309112 = -30 --> 16 holes F =2V-4: 309112 != 309052-4 (-64) 2E=3F: 927336 = 927336 (0)

total defect index = 32

so -30 in this case. Is that what you wanted?

Cheers Bruce From: freesurfer-bounces@nmr.mgh.harvard.edumailto:freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edumailto:freesurfer-bounces@nmr.mgh.harvard.edu> On Behalf Of Melissa Thalhammer Sent: Thursday, February 1, 2024 5:31 AM To: Freesurfer@nmr.mgh.harvard.edumailto:Freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] Euler number calculation from number of holes

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Dear FreeSurfer experts,

I want to calculate Euler numbers for QC but I am not sure how to get them. I read some posts here and figured out that I get the number of holes in a surface with mris_euler_number -o $OUTPUT_FILE $subject/surf/?h.orig.nofix. Is it correct that I need to calculate the Euler number subsequently as the sum of holes of both surfaces and then Euler_number=(number_of_holes*(-2)) -2 ?

Best, Melissa