[MINC-users] Conversion of volume

[Ed Gronenschild]

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