Dear Doug and freesurfers, 

Referring to the topic we already talked about above, I am still wondering wether the pial view of the Heschl's gyrus (transverse temporal gyrus) of an individual subject (not averaged) is displayed correctly, for the calculated surface in mm^2 from the aseg-file is for atlas I (Desikan 2006) always larger than for atlas II (Destrieux 2010) - but as the attachment shows  (individual Heschl's Gyrus of 20 subjects) atlas II consistently looks considerably larger. What am I doing wrong? Or can the pial surface not conclusively be interpreted refering to the calculated aseg results?

Thanks in advance, 


2013/4/2 Douglas N Greve <greve@nmr.mgh.harvard.edu>
Yea, the appearance of the average subject pial surface can be very
different depending up on the input subjects. The xyz for a pial vertex
are just the average mni305 xyz for that vertex averaged over the input
subjects. Since it is dependent on a 12DOF transform, it will not
accurately represent any surface. The overlays (thicknesses, etc) are
registered using the surface-based high DOF registration, so their
averages mean something. But the pial surface should only be used for
display.
doug


On 04/02/2013 01:07 PM, Bruce Fischl wrote:
> 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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Douglas N. Greve, Ph.D.
MGH-NMR Center
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