Donna/John,

Is it possible to apply the distortion correction to individual tiles?

Best Regards, Donald McLaren
=====================
D.G. McLaren
University of Wisconsin - Madison
Neuroscience Training Program
Tel: (773) 406 2464
=====================
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----- Original Message -----
From: Mateus Joffily <[EMAIL PROTECTED]>
Date: Tuesday, January 30, 2007 12:29 pm
Subject: Re: [caret-users] ROI center of gravity
To: "Caret, SureFit, and SuMS software users" <caret-users@brainvis.wustl.edu>


> Hi Donald,
> 
> Thanks for your comments.
> 
> I would like to propose a 'new' method for calculating the surface's 
> COG. To avoid the nodes density problem, I think it would be 
> reasonable 
> to calculate the COG of every tile on the surface and, after, to 
> calculate the COG of the whole surface summing the COG of each tile 
> multiplied by its own area and divided by the total surface area. I 
> have 
> done some tests using this method and compared the results with 
> Caret's 
> method.
> 
> On the attached capture (cog_m1.jpg), you can see a flat map of the 
> primary motor cortex. Depending on the method used (caret vs. 'new' 
> method) the COG can be shifted of up to 10mm. The 'new' method shows a 
> 
> COG more superior, consistent with the lower concentration of nodes at 
> 
> this region of the surface. Capture 'cog_m1_zoom.jpg' is just a zoom 
> in 
> on the tiles' CoG (green points).
> 
> I would appreciate any comment on this method.
> 
> I couldn't find the paper you cited. I guess it hasn't been published 
> 
> yet. Do you know when it will be available for download?
> 
> Best regards,
> Mateus
> 
> DG MCLAREN wrote:
> 
> >Mateus,
> >
> >You raise a good point. 
> >
> >In practice, it seems that you should keep the uneven distribution of 
> nodes. The reason is as follows: If you resample the nodes to a more 
> sparse uniform distribution, then you will distort the surface to some 
> degree. The surface distortion will inevitable shift the center of 
> gravity. I had thought about using the border points of a cluster to 
> calculate the region; however, it seems that approach may unequally 
> weight some parts of the cluster if there is an odd shape. It might be 
> interesting to do a comparison between these methods.
> >
> >In the end, it probably doesn't matter how you do the calculation for 
> COG, as they should be similar, as long as the method is reported. I 
> should also note, a recently accepted article: Cortical network for 
> vibrotactile attention: A fMRI study in Human Brain Mapping describes 
> the method and uses the traditional method; so there is an established 
> standard that one could rely on and cite in future work.
> >
> >Best Regards, Donald McLaren
> >=====================
> >D.G. McLaren
> >University of Wisconsin - Madison
> >Neuroscience Training Program
> >Tel: (773) 406 2464
> >=====================
> >This e-mail contains CONFIDENTIAL INFORMATION which may contain 
> PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED 
> and which is intended only for the use of the individual or entity 
> named above. If the reader of the e-mail is not the intended recipient 
> or the employee or agent responsible for delivering it to the intended 
> recipient, you are hereby notified that you are in possession of 
> confidential and privileged information. Any unauthorized use, 
> disclosure, copying or the taking of any action in reliance on the 
> contents of this information is strictly prohibited and may be 
> unlawful. If you have received this e-mail unintentionally, please 
> immediately notify the sender via telephone at (773) 406 2464 or email.
> >
> >----- Original Message -----
> >From: Mateus Joffily <[EMAIL PROTECTED]>
> >Date: Friday, January 26, 2007 12:12 pm
> >Subject: [caret-users] ROI center of gravity
> >To: "Caret, SureFit, and SuMS software users" 
> ><caret-users@brainvis.wustl.edu>
> >
> >
> >  
> >
> >>Hi,
> >>
> >>I would like to calculate the center of gravity (COG) of a surface 
> >>ROI. 
> >>I see that 'Surface Region of Interest':'Statistical Report' gives 
> me 
> >>
> >>that information. However, if the nodes distribution over the 
> surface 
> >>is 
> >>not uniform, the COG is biased toward the more dense regions.
> >>I understand that, if someone wants to calculate the COG, taking 
> into 
> >>
> >>account the nodes-density, this is the right calculation. But, if I 
> 
> >>suppose that the surface density is uniform, is there a way of 
> >>calculating the COG avoiding the nodes distribution effect?
> >>
> >>Thanks,
> >>Mateus
> >>_______________________________________________
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> >>    
> >>
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> >
> >
> >  
> >
> 
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