I am more or less a complete novice in the field of 3D modeling. I understand the basics of a polygon mesh and a texture; however, it was always my understanding that 3D models were, effectively, "hollow" inside the mesh, in the same way that a plastic skeleton Halloween decoration is hollow. It possesses a surface, but no internal density. This understanding has always worked well for me, as I primarily work with photogrammetry-created 3D models, for which this is undoubtedly true.
In my latest project, however, I am being asked to work with 3D models created using CT scan data and Slicer. Unlike photogrammetry images, CT scans do care about internal density and structure. I know Slicer can be used to create 3D models from CT scan images. What I'm uncertain about, however, is whether Slicer creates truly "solid" models from this data -- models which have internal density rather than simply a mesh "skin", where the "inside" of the model is programmatically distinct from the "outside" -- or whether it simply create a multilayered but still fundamentally hollow mesh (or series of meshes) based on boundaries between areas of different densities.
Is this a meaningful distinction? Am I fundamentally misunderstanding how the surface/internal geometry of 3D models works? Any advice is welcome.
(I took my best guess as to where to ask this question -- if this is outside the purview of this site, please let me know! If you know another place where I could go asking for answers, I would also appreciate that information. Thank you so much!!!)