Artefacts when overlapping volumes

[chriskisskiss]

Hello,

I added two nifti files as scalars, which are overlapping and joined in a Join Component node. The structural image (cranial MRI) is trimmed via a Cube and Cut node.

However, there is clearly an artefact line projected on the cut surrounding the nifti colored in red. I am no blender expert, maybe I am missing the obvious.
Any advice?

Thank you very much,
Christian