Introduction
   
    DSI Studio provides several ways to perform along tract quantitative analysis as opposed to voxel-based analysis. The paradigm behind along tract analysis is that the analysis is based on the tracking results to confirm the location of the fiber bundle. The located white matter regions are then observed for changes in quantitative indecies such as FA, ADC. To carry out such analysis, the workflow is as follows:

    1. Perform fiber tracking
    2. Save along tract quantitative indecies.
    3. Anlysis the exported quantitative indecies.

    The fiber tracking is explained in another section. The information related to analysis is detailed in the following content.


Save along tract quantitative indecies

    In the tract 3D presentation window. The save along tract quantitative indecies functions are located on the main menu. "File"-> "Save Tracts".

    DSI Studio calculate along tract quantitative values through interpolation, obtaining the "Nearest FA" as for FA. The reason for this interpolation is that the tract points may not pass through the center of the voxel exactly. So, for each point on the tract, DSI Studio samples the quantitative values provided by 8 nearby voxels and perform trilinear interpolation to obtain the "Nearest" quantitative value of the point. The quantitative values of a tract will be exported as a line in sequence whereas the FA values of different tracts are saved in different lines as follows: (The values are separated by a space)

    [1st point 1st tract] [2nd point 1st tract]...
    [1st point 2nd tract] [2nd point 2nd tract]...
    [1st point 3rd tract] [2nd point 3rd tract]...

Note: For DSI or QBI, use along tract gfa instead.


Analyze the exported quantitative indecies.

    A simple way to analysis the exported quantitative information is by loading the file in Microsoft Excel. Open the text file in Excel using "space" as the separator and the quantitative values will be imported. The quantitative indices of diffferent tracts can be averaged if the tracts are aligned properly. A quick way to align the tract is to use "Cut" function to trim the fiber bundles so that the tracts can be viewed as alinged ("Cut" function is detailed in tract editing section).

   After the quantitative values of the aligned tracts are averaged, the averaged values can be plotted to demonstrate the pattern along the fiber bundle.