Hi,
On Fri, Jul 10, 2015 at 1:18 AM, Darren Yeo <jia...@gm...> wrote:
> Hi MarsBar users,
>
> I created several spherical ROIs of radius 5 mm, each with a different
> center coordinate. However, they turn out to have very different volumes
> (and number of voxels). They have volumes of either 448, 560 or 648 cubic
> mm. I created several other ROIs using the same radius but with different
> centers, and each sphere results in either one of the 3 volumes.
>
> On the other hand, when I created spherical ROIs in BrainVoyager using the
> same radius, I get a consistent volume of 515 cubic mm.
>
> Is there an explanation for the inconsistency in MarsBar? And is there a way
> to ensure more consistent creation?
How are you assessing the volume of the ROI?
I'm sure what is happening here, is that your center is sometimes in
the center of a voxel, and sometimes not. This in turn makes a
difference as to which voxel centers are within the sphere, when
sampling on a voxel grid. I suspect that BrainVoyager gives the
volume without consideration of the voxel grid, but of course you
can't avoid the voxel grid when you do the resampling from the ROI.
Best,
Matthew
|
