Those values are at the endpoints of the tracts. As the median tract may be a bit longer or shorter in different subjects, the endpoints don't always have corresponding points in all subjects 
From: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> on behalf of Hua, Jessica <jphc55@mail.missouri.edu>
Sent: Thursday, April 23, 2020 4:01 PM
To: freesurfer@nmr.mgh.harvard.edu <freesurfer@nmr.mgh.harvard.edu>
Subject: [Freesurfer] Trac-All NaN
 

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Hi FreeSurfer,

I ran the trac-all -stat command on some of my participants, and I noticed that some of the values that were outputted contained NaN.  Why are the values coming out as NaN?

fmajor_PP.avg33_mni_bbr.AD_Avg.txt
S11018a_LGI S11019a_LGI S11021a_LGI 
NaN NaN 0.00109668
0.00116704 NaN 0.00110631
0.00118262 NaN 0.00113231
0.00119589 NaN 0.00116401
0.00121558 NaN 0.00117549
0.00123733 NaN 0.00119309
0.00126087 NaN 0.00123177
0.00127355 0.00116328 0.00127236
0.00126695 0.00115413 0.00129993
0.00125837 0.00117334 0.00131861
0.00125611 0.00117423 0.00134501
0.00130347 0.00117161 0.00135121
0.00133526 0.00117097 0.00136288
0.00135801 0.00116546 0.00136839
0.00138131 0.0011961 0.00141117
0.00137605 0.00126803 0.00143167
0.00139927 0.00132198 0.00144947
0.00140814 0.00135481 0.00145095
0.00141403 0.00136342 0.00144231
0.00143846 0.00136409 0.0014307
0.00144842 0.00134806 0.00141466
0.00144669 0.00138324 0.00139904
0.00144974 0.00143263 0.00139749
0.00146505 0.00145596 0.00143352
0.00149473 0.0014523 0.00144366
0.00150771 0.0014622 0.00144891
0.00151567 0.00148269 0.00147786
0.0015513 0.00151399 0.00153047
0.00158431 0.00155476 0.00160898
0.00163524 0.00162621 0.00166298
0.00166918 0.0016651 0.0016538
0.00165915 0.00165803 0.00169534
0.00171513 0.00164646 0.00176355
0.00178509 0.00167836 0.00179073
0.00186456 0.00175883 0.00181997
0.00187805 0.00183493 0.00178465
0.00189962 0.00187421 0.00175515
0.00192235 0.00189781 0.00171387
0.0019091 0.00184765 0.00160073
0.00191175 0.00181558 0.00157862
0.00191679 0.00182829 0.00165907
0.00185513 0.00185947 0.0017003
0.00181572 0.00189271 0.00172307
0.00181154 0.0018763 0.00159418
0.0018311 0.0018657 0.00159179
0.00172958 0.00189407 0.00164795
0.00165341 0.00191997 0.00167435
0.00156794 0.00190814 0.00168963
0.00146072 0.001859 0.00172164
0.00138372 0.00178192 0.00175954
0.00136893 0.00170486 0.0018261
0.0013654 0.00164533 0.0018264
0.00135974 0.00155251 0.00176598
0.00137226 0.00149038 0.00166574
0.00133654 0.00146834 0.00152383
0.00134757 0.00148128 0.00138086
0.00136271 0.00147022 0.00132929
0.00136545 0.00144934 0.00127674
0.00137979 0.00145088 0.00125313
0.00137398 0.00151918 0.00125802
0.00137699 0.00151537 0.00126461
0.00136867 0.00146195 0.00126159
0.00136882 0.00140568 0.0012639
0.00134777 0.00138923 0.00126469
0.00127934 0.00138564 0.00127229
0.00122813 0.00138057 0.00128295
0.00118596 0.00138419 0.00129555
0.00117204 0.0013933 0.00131012
0.00114282 0.0013934 0.00129255
0.00114104 0.00141831 0.0012982
0.00116965 0.00141932 0.00128999
0.00118427 0.00139441 0.00128321
0.00117267 0.0013619 0.00127428
0.00117105 0.00133817 0.00124349
0.00114046 0.00131501 0.00121045
NaN 0.0012865 0.00117847
NaN 0.00126657 0.00114993
NaN 0.00123952 0.00113779
NaN NaN 0.00112863
 
Jessica

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Jessica Hua, M.A.
Cognitive and Emotional Control Lab
Doctoral Candidate Clinical Psychology 
University of Missouri