Registration matrix files

If you want to visualize reconstructed fibers in the geometry of another image than the DWI (i.e. the T1 image), you must specify a registration matrix (affine) when creating the DTI-study. As said in Sec. 3.2, you must specify the file containing the registration matrix that has to be applied to go from DWI geometry to the new image geometry.

In the second screen of the DTI importation wizard, click on ``Load Aff. Matrix'' and choose the file that contains the matrix. Fig. A.2 shows an example of this file. First is specified resolution information. First line corresponds to the DWI image resolution, while the second line to the new image resolution (T1 for instance). Image sizes on the 3 axes are indicated followed by the voxel size in mm. After this resolution information, the coefficients of the transformation matrix to apply are succesively specified. Transformation is divided in a linear transform and a translation :

where A is the affine transform matrix and T the translation vector.

In the matrix file the coefficients are sorted as followed (column-wise):

For instance the identity transformation would be:

Once you have loaded the matrix file (extension .mat), please verify it has been loaded by looking at the log window (error panel) and check that there hasn't been any file reading error. See Fig. A.2 for an example.

Figure A.2: On the left is shown the visualization of reconstructed fibers with a T1 image loaded. To map the fibers in the T1 image geometry, a file has been loaded when creating the study. You can see on the right the file used in this example. In this file are succesively specified the resolution and voxel size information of the DWI and the T1 image. Then the 12 transformation matrix coefficients are specified.