Fiber assignment by continuous tracking algorithm (FACT)

Fiber assignment by continuous tracking (FACT(FACT) algorithms are a commonly used deterministic post-processing algorithmsalgorithm for magnetic resonance tractography studies.

In these algorithms, axonal fiber bundles are reconstructed - voxel by voxel - following the direction of the main eigenvector. The beginning of this reconstruction process can take place in different ways:

• from a single voxel (seed point);
• from several independent voxels;
• from several voxels belonging to the same ROI (Region Of Interestregion of interest (ROI).

The use of a single voxel or several independent voxels is not advisable, because they tend to generate too thin fibers with an approach to the real neural pathway not very reliable. The most reliable approach is the use of several voxels belonging to the same ROI^4,5.

The characteristic of this particular type of algorithm, totally based on data, is the remarkably fast computational speed. Therefore, although FACT algorithms create some predictable errors, they may in some cases be preferred to more accurate algorithms ^2,3.