Windows 10, slicer 4.11.
This is a common question I think. My apologies for asking this simple question but after reading all the manuals, definitions, and answers in the support, I still cannot understand.

Issue: I have produced a 3D model of the frontal sinus cavity by cropping the region and applying threshold value. Now, I want to know the volume of my 3D frontal sinus cavity. I click on segment statistics to get the volume. But there is three volume given which is computed from labelmap statistic, scalar volume statistic and closed surface statistic.

May I know the difference between these three in a brief/simple term?
and which one of these three should I choose to represent the volume of my reconstructed 3D model?

They are all different ways of calculating the same basic quantity but may have different behaviors based on the size/shape of your object and images. If these descriptions are not clear perhaps we can work together to improve them:

I need a few further clarification.
Is closed surface means it is empty inside?

For scalar volume (values are computed for only that part of the segments that overlap with the bounding box of the scalar volume), I dont understand the āsegments that overlapā. How can I know it is overlap?
Where is the bounding box of scalar volume? Is it the white box in the 3D pane?

A segment in Slicer is a solid 3D object. It is not empty inside. A closed surface representation specifies a segment by a closed surface boundary. Anything within that closed surface is inside the segment.

Iāve rephrased the text. Please check and let us know if it is clear now.

I meant that it is within the scalar volume. Iāve removed the ābounding boxā term to avoid confusion.