Diffusion properties along trajectory

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[edit] Two ways to compute fiber group properties.

1. Aggregate over all nodes in all the fibers comprising the fiber group.

In dtiFiberUI choose your fiber group and click "Analyze"->"Fibers"->"Summary" to obtain mean and range for FA, MD, ADC, RD, fiber length and number of fibers.

2. Compute diffusion properties ALONG the trajectory of the fiber group segment between two ROIs. This method uses distance-weighted averaging [add link] of tensor eigenvlues across the fibers at each of N points (you specify N). Essentially, the fibers that are traveling close to the "core" of the fiber group will contribute more to the average property estimates.

[edit] Computing diffusion properties along the trajectory

[edit] Example

1. Start with two ROIs and a fiber group.

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Set your current fiber group to the one you want analyzed. Click "Analyze"->"Fibers"->"Diffusion properties along the trajectory".

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2. You will be prompted to chose the two ROIs which define the FG segment of interest. You have to choose two, and only two ROIs from the list of currently loaded ROIs. You will then be prompted to choose the number of nodes (steps within the FG segment of interest for which the properties will be computed).

[edit] Results

1. This will generate 4 plots (for FA/MD/AD/RD). Each plot contains two panels. The right panel shows a plot of the respective diffusion-based property from node 1 to last node. The left panel shows a 3D representation of the fiber group as a tube, where the tube's width reflect the amount of spatial dispersion of the fibers at that node. The core of the tube travels through the center of mass of the fiber group. You can click on "3D rotate" icon in the figure window and rotate the plot. Axes are labeled as left/right, anterior/posterior and inferior/superior. Axes as scaled in ACPC coordinates for this b0. Also note that the colors of the tube segments correspond to the property value (e.g., peak FA along the fiber group would be showed as bright red).

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2. Two more fiber groups will be added to the "fiber groups" in dtiFiberUI GUI: (1) Your originally chosen fiber group cropped to the two ROIs you chosen. (2) Center-of-mass ("core") trajectory of the cropped fiber group. This will be saved as a single fiber created by aggregating the locations of all the fibers in the fibergroup. This "core" fibers in some cases may be traveling through the regions where there are no real fibers from our fiber group. (This may happen, for example, if your fiber group is comprised of several spatially distinct bundles).

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