Keep the hand-drawn segmentation after interpolation

Hello all. I’m working with a non-isotropic MRI, only the sagittal view with 31 slices. More info can be found in this post: Segmentation using curves . I drew the segmentation on each slice, however, the 3D shape is not smoothed and there are lots of steps and many holes:

One suggestion was to interpolate the slices using Crop module. This ended up with hundreds of slices (e.g., 600), but I don’t want to go through all. I want to interpolate the segmentation as well.

My plane now is to keep the initial hand-drawn segmentation and Fill between the intermediate slices after interpolation. However, my initial segmentation appears in all intermediate slices and the “Fill between slices” doesn’t actually work.

By any chance, is there any way to handle this? (I can draw the segmentation after interpolation, but I cannot find the original slices)

Thank you in advance.

Here is a video that better explains the issue.

This also happens even if I draw segmentation on only one slice after interpolation.