How can I compare 'small' and 'big' Talairach box datasets?
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Q67. How can I compare 'small' and 'big' Talairach box datasets?
This question arises when people have a bunch of older datasets that were transformed to Talairach-Tournoux space when the transformed box only extended to z=-55 mm. In March 1996, I extended the 3D grid of the +tlrc datasets to z=-65 mm - the reason for this was that for many subjects, the z=-55 mm level did not get the whole cerebellum. To maintain backward compatibility, the Big Talairach Box? toggle box was added to the Markers control panel. If this toggle is turned off, then the old z=-55 mm lower limit is used; otherwise, the new z=-65 mm is used.
The "best" solution is to go back and retransform the old datasets to the Big box. This is a fair amount of trouble, though. If you don't care about activation in that very inferior region, then you can extend the old (small box) datasets to have the same size as the new (Big box) datasets using the program 3dZeropad. This will add slices of all zeros, which will make the dataset .BRIK files the same size, and thus be able to be compared (e.g., via 3dANOVA).
If you have used the default 1 mm voxel size in +tlrc coordinates (as almost everyone does), then you need to add 10 zero slices at the inferior edge of the small box datasets. You can do this with a command like
3dZeropad -I 10 -prefix fredBig fredSmall+tlrcThe new dataset (fredBig+tlrc) is what you want. If you used some other voxel size, then you'll have to figure out the amount of zero padding yourself (hint: use 3dinfo).
[03 Oct 2000] You can now use the new Dset Zeropad plugin to do the same thing interactively.
[Answer added 11 Jul 2000 - edited 03 Oct 2000]
This FAQ applies to: Any version.
