[Freesurfer] Talairach coordinates

2008-06-29 Thread Feng-Xian Yan 
Hi,
I have some problems about surface coordinates.
After running the qdec and analyzed my data(cortical thickness), I display a
plot of the data for a particular vertex by left-clicking on a point while
holding down the Ctrl key. It shows a plot and its plot window shows this
vertex's *surface coordinates.*
  1) Does the surface coordinates differ from Talairach coordinates?
  2) If yes, can I translate the surface coordinates to Talairach
coordinates?
  And how do I do? Does Freesurfer have some methods to do that?

Thank you in advance.
Feng-Xian
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[Freesurfer] About the area of the vertices in the surfaces

2008-06-29 Thread jorge luis 
Hello all
I have some questions:

I would like to know how freesurfer computes the vertex’s wise areas? eg. 
thouse in lh.area. 

It should be expected that the sum of the areas of all the vertices across a 
surface equals the total surface area?

To be much specific:
 Can I compute the area of an 'activated' cortical  ROI  in the average subject 
by simply adding the area of all its vertices? 

In adavance thank you

Jorge
Phd Student





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Re: [Freesurfer] About the area of the vertices in the surfaces

2008-06-29 Thread Bruce Fischl 

Hi Jorge,

yes, the area of a vertex is 1/3 of the area of all triangles that it is 
a member of, and it should sum to the area of the surface. The average 
subject has a correction factor that accounts for the "lost" area due to 
averaging, so you'll need to apply this if you want it to be in true mm 
(in the average sense across your subjects). mris_info 
~/local_subjects/fsaverage/surf/lh.white

reading group avg surface area 864 cm^2 from file
Reading in average area 
/homes/4/fischl/local_subjects/fsaverage/surf/lh.white.avg.area.mgh

SURFACE INFO 
type: MRIS_TRIANGULAR_SURFACE=MRIS_ICO_SURFACE
num vertices: 163842
num faces   : 327680
num strips  : 0
surface area: 70394.8
AvgVtxArea   0.429650
AvgVtxDist   0.757401
StdVtxDist   0.227951
group avg surface area: 86444.7
.
.
.

thus, you would need to multiply your areas by 86444.7/70394.8 to get mm in 
the average cross-subject sense.

cheers,
Bruce

On Sun, 29 Jun 
2008, jorge luis wrote:



Hello all
I have some questions:

I would like to know how freesurfer computes the vertexÿÿs wise areas? eg. 
thouse in lh.area.

It should be expected that the sum of the areas of all the vertices across a 
surface equals the total surface area?

To be much specific:
Can I compute the area of an 'activated' cortical  ROI  in the average 
subject by simply adding the area of all its vertices? 


In adavance thank you

Jorge
Phd Student





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Consigue una que te guste de verdad - millones de direcciones de correo 
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http://es.docs.yahoo.com/mail/nueva_direccion.html

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