Computing Anisotropy

You can compute the degree of anisotropy, which is a measure of how highly oriented substructures are within a volume, for any selected region of interest using the mean intercept length (MIL) or star volume distribution (SVD) method (see Anisotropy for information about these methods).

Right-click the region of interest you want to analyze and then choose Compute Anisotropy Using and a computation method in the pop-up menu to open the Set Anisotropy Parameters dialog, in which you can a select the settings for the computation. Results will appear in a message box after the computation is complete, as shown below.

Anisotropy computation

For an isotropic (perfectly oriented) system, the degree of anisotropy (DA) is equal to 0. As the system becomes more anisotropic (less well-oriented), the DA increases to some value less than 1.

The settings for computing the degree of anisotropy, for example of segmented trabecular bone, are available in the Set Anisotropy Parameters dialog, shown below.

Set Anisotropy Parameters dialog

Refer to the table below for a description of the settings applicable to anisotropy computations.

Settings for computing anisotropy
  Description
Max iterations Is the maximum number of random points in the sample that will be analyzed. Fitting will stop automatically after this number is completed or if the coefficient of variation (tolerance) is reached.
Sampling Is the resolution, or distance between subsequent samples along each vector. You should note that the entered value can be equal to the voxel size of the input region of interest.
Orientations Is the number of lines to analyze per sampling sphere.
Min iterations Is the minimum number of random points in the sample that will be analyzed.
Radius Is the radius of the sampling sphere, which determines the length of each sampling vector.
Tolerance Is the coefficient of variation. Sampling new random points will continue until either a coefficient of variation equal to the tolerance is reached or the maximum number of iterations is completed.
  1. Right-click the region of interest you want to analyze in the Data Properties and Settings panel.
  2. Do one of the following:
    • Choose Compute Anisotropy Using > Mean Intercept Length (MIL).
    • Choose Compute Anisotropy Using > Star Volume Distribution (SVD).
  3. Enter the required settings in the Set Anisotropy Parameters dialog.

    Refer to the table Settings for computing anisotropy for information about the available parameters.

  4. Click OK

    When processing is complete, the result appears in the Anisotropy dialog.