Diffusion gradients files

To perform DTI analysis such as tensor estimation and fiber tracking, importation of Diffusion Weighted Images (DWIs) is not enough. Indeed information about the gradient directions used for the acquisition is necessary. As said in section 3.2, you must load a text file containing these gradients in the importation wizard. An example of this file is shown in Fig. A.1. It is a simple text file containing a succession of numbers. First integer is the number of gradients. For example if the acquisition has been performed in 6 different diffusion directions, plus the acquisition without gradient (the B0 image), this integer will be 7. Then there has to be the succesion of 7 gradient directions (one at each line). A gradient direction corresponds to the 3 coordinates (real numbers) of the direction vector. Directions have to be sorted to respect the alpha order of the DWI files (see Fig. A.1).

Figure A.1: On the left is shown a part of the DTI Importation wizard's second screen (see Sec. 3.2). You see an example of the importation of a B0 image and 6 DWI, with their corresponding gradient directions. As the B0 image has no gradient, its corresponding gradient direction is null. On the right, you can see the corresponding text filled that has been loaded for this example. It contains the gradients, one null + 6 gradient directions, preceded by the total number of them (here 7). These directions have to be sorted to respect the alpha order of the DT-MR files.