9 Computing Volumes and Statistics

Once you have a segmentation, it is important to get some information about it. For this, there is a volumes and statistics option in ITK-Snap that allows you to see the volume corresponding to each label in your segmentation as well as intensity statistics for each label.

STEP 1

Open image and corresponding segmentation.

STEP 2

In the task bar, select Segmentation -> Volumes & Statistics

Here, you will see information about:

​​Number of voxels that belong to the structure

Volume of the structure (in cubic millimeters)

Mean image intensity inside the structure

Standard deviation of the image intensity in the structure

STEP 3

Select Export and specify a filename with a .txt extension and click OK.

STEP 4

Import text file into a spreadsheet application for analysis. For analysis, it is important to note that you cannot use raw structural volumes in your models. This is because you need to account for total estimated intracranial volume (ICV).

To do this, refer to the methodology section of Raz et al. (2015). You may correct for ICV via a linear equation: Volumeadj = Volumerawi - b(ICVi - Mean ICV), where Volumeadj is the adjusted regional volume, Volumerawi is the original volume for an individual, b is the slope of the ROI volume regressed on ICV, and Mean ICV is the sample mean of ICV (Raz et al., 2015).