Re: [Freesurfer] Discrepancy between surface data of Heschl's gyrus and its image

the average subject is constructed by specifically trying to normalize out differences in folding so I wouldn't try to infer anything from it cheers Bruce

On Tue, 2 Apr 2013, Klein, Holger wrote:

Hi Bruce,  Thanks for the quick reply. I took the individual surface values from every subject's aseg-file and calculated the mean. Visualization was made in tksurfer with the average subject.

Thus, I am still wondering about this discrepancy.

Any other hints?

Thanks, H

2013/4/2 Bruce Fischl fischl@nmr.mgh.harvard.edu Hi Holger

  how did you calculate the surface area? And how are you visualizing it? I wouldn't use the surface area of
  the average subject for anything other than visualization as the coordinate system is not linear. You need to
  compute the surface area in the individual subject coordinates or take the jacobians into account.

  cheers
  Bruce


  On Tue, 2 Apr 2013, Klein, Holger wrote:

  Dear Freesurfers, 
  I averaged 42 subjects with make_average_subject focusing on Heschl's Gyrus and finally got the image
  attached (for both
  atlases (Desikan = Atlas I, Destrieux = Atlas II).

  Gray matter surface calculations for Heschl's gyrus showed the following mean values (in mm^2):
  Atlas I lh = 439 (SD 60), rh = 323 (SD 46)
  Atlas II lh = 340 (SD 70), rh = 253 (SD 47)

  Heschl's gyrus depicted in the attached image looks considerably larger for Atlas II, but the surface
  analysis gives me
  smaller values for mean surface calculation (Atlas II < Atlas I)

  How can that be explained? 

  Thanks in advance

[cleardot.gif]

Holger

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