Dear FreeSurfer experts,
I computed distances on the cortex surface using mris_pmake on a data set
acquired at a 3T scanner (using an MPRAGE sequence and protocol recommendations
for FreeSurfer). The exact syntax of the distance computation was:
mris_pmake --subject SUBJECT_ID --hemi lh --surface0 smoothwm --curv0 sulc
--curv1 sulc --mpmOverlay euclidean --mpmProg pathFind --mpmArgs
startVertex:66245,endVertex:59104 .
Subsequently, the euclidean distance was computed using the Talairach
coordinates displayed by tksurfer if the startVertex and the stopVertex are
selected:
distance_euc =
sqrt[(startTal_x-stopTal_x)^2+(startTal_y-stopTal_y)^2+(startTal_z-stopTal_z)^2]
.
As you all know from your Tutorials, the in-surface distance must be larger or
equal to the euclidean distance. Surprisingly, in the majority of cases
investigated the opposite is computed. Typical distances calculated are in the
range of 7 mm. Do you have an explanation for this outcome and a possible
solution how it can be corrected? I am using FreeSurfer 5.1 and did not
encounter any other problems in data evaluation. Any help us highly appreciated!
Sincerely yours
pfannmoe
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