Re: [Marsbar-users] Inconsistent spherical ROIs created

[Darren Y. <dar...@va...>]

Hi Dr Brett,

I’m resampling against images preprocessed in SPM and used Conn toolbox,
which I believe uses the same 2-mm template in SPM. So, all structural,
functional, and ROIs are within the same MNI standard space.

I understand the part regarding whether voxels are considered to be within
the boundaries of the sphere or not, but I’m still not sure if I understood
why the sphere center will not be a voxel center in the first place if they
are created in the same SPM space (of 2-mm dimensions).

Thanks!

Best,
Darren


On Fri, Jul 10, 2015 at 10:31 AM, Matthew Brett <mat...@gm...>
wrote:

> Hi,
>
> On Fri, Jul 10, 2015 at 4:13 PM, Yeo, Darren J
> <dar...@va...> wrote:
> > Hi Dr Brett,
> >
> > Thanks for your prompt reply!
> >
> > For the ROIs I created in MarsBar, I referred to the volumes indicated in
> > the MarsBar viewer as well as using AFNI¹s 3DBrickStat function to count
> > the number of voxels (and multiplying by 2^3). The computed volumes
> > corroborated with each other using both methods of assessment.
> >
> > For the ROIs I created in BrainVoyager, I extracted the number of voxels
> > from the ROIs, which are the same ‹ 515 1-mm isotropic voxels.
> >
> > A basic question that I¹m grappling with is: If I specify the center of
> > the sphere using MNI coordinates, and I build the ROI in MNI standard
> > space, wouldn¹t the center (always?) be in the center of a voxel?
>
> It depends what image you are resampling against.  By default Marsbar
> displays the image on the 2mm templates that come with SPM.
>
> Unless you do something to them, marsbar stores the spherical ROIs as
> spheres (center and radius) and then applies them when you resample
> from the given images.    When resampling, the voxel is taken to be
> within the sphere if the the voxel center coordinate is within the
> sphere.
>
> Cheers,
>
> Matthew
>
>
> ------------------------------------------------------------------------------
> Don't Limit Your Business. Reach for the Cloud.
> GigeNET's Cloud Solutions provide you with the tools and support that
> you need to offload your IT needs and focus on growing your business.
> Configured For All Businesses. Start Your Cloud Today.
> https://www.gigenetcloud.com/
> _______________________________________________
> Marsbar-users mailing list
> Mar...@li...
> https://lists.sourceforge.net/lists/listinfo/marsbar-users
>



-- 
Darren Yeo
Graduate student in Child Studies
Peabody College, Vanderbilt University
http://jiansh.wix.com/darrenyeo