On 9/18/2020 12:12 PM, Billah, Tashrif wrote:

Hi there,

How is the rightmost column in `mri_convert -c` calculated?

I have the following fslhd (relevant fields shown only) in a NIFTI image:

```

dim1 208
dim2 300

dim3 320

qto_xyz:1 0.799690 0.022176 0.001352 -86.687996

qto_xyz:2 -0.021442 0.783122 -0.162051 -62.728546

qto_xyz:3 -0.005816 0.161952 0.783414 -174.620270

qto_xyz:4 0.000000 0.000000 0.000000 1.000000

```

That looks like it is the qform matrix in the nifti file

After `mri_convert -c`, mri_convert reports the following (relevant fields shown only) in the MGZ image:

```

voxel to ras transform:
-1.0000 -0.0000 0.0000 128.0225

-0.0000 0.0000 1.0000 -101.4184

0.0000 -1.0000 -0.0000 102.4140
0.0000 0.0000 0.0000 1.0000

```

Shouldn't the right-most column be:

128.5

-128.5

128.5

1

The numbers are (256+1)/2=128.5

Not necessarily. That matrix still converts from col-row-slice to scanner RAS (or whaterver the qform space is)

Best,

Tashrif

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