Length of contact line in an image

Dear all, I have CT scans of few layers. How to detect the volume of each layer or detect the contact line between layers?

I tried 'edge', but it doesn't work. Then follow an instruction to detect cell https://au.mathworks.com/help/images/examples/detecting-a-cell-using-image-segmentation.html, but my picture seems to be tricky. When I do 'imdilate' to close boundary line, it also closes gaps between layer. Then tried to use 'imclose' with disk and line, but it doesn't work neither.