[MINC-users] Conversion of volume

[Ed Gronenschild]

Hello,

Since I didn't receive any response I tried to figure it out myself.
I think that I'm wrong about the proposed conversion. I guess
that it is much simpler:

vol_native = vol_tal / scale_factor
		= vol_tal / 1.4388
		= vol_tal * 0.6950

(see eg. Pruessner et al, J. Neurosci, 2001, 21(1), 194-200)

I hope that I can have some feedback now.

Ed

On 7 Sep 2006, at 14:44, Ed Gronenschild wrote:

> Hello
>
> I'm doing volumetric measurements of brain structures in
> stacks which have been transformed linearly in stereotaxic
> Talairach space (mritotal) en resampled in 1.00 mm cubic
> voxels (mincresample). The native voxel size is 0.94 * 0.94
> * 1.50 = 1.3254 mm^3). To derive the volume in native
> space I do the following:
>
> Let's define the native voxel size "voxel_size_native",
> and the Talairach voxel size "voxel_size_tal". Furthermore,
> the native volume is defined as "vol_native" and the volume
> in Talairach as "vol_tal".
>
> With xfm2param I derive the following transformation
> parameters:
>
> -center         0.00000    0.00000    0.00000
> -translation -129.92584  111.43100   97.71683
> -rotation      -7.68466   -1.81075   -0.82142
> -scale          1.06879    1.11325    1.20931
> -shear          0.00000   -0.00000   -0.00000
>
> The scale factor ("scale_factor") is the product of the scale
> factors in X,Y, and Z, so
> scale_factor = 1.06879 * 1.11325 * 1.20931 = 1.43882.
> By the way, this is equal to the determinant of the transformation
> matrix.
>
> The conversion from Talairach to native is then:
>
> vol_native = vol_tal * voxel_size_native / voxel_size_tal /  
> scale_factor,
>
> or
>
> vol_native = vol_tal * 1.3254 / 1.0 / 1.4388
>
> 		= vol_tal * 0.9211
>
> Can you agree with me?
>
> Regards,
>
> Ed