Thanks, I hadn’t noticed this option before. However, this results in the segmented tube being semi-transparently rendered in front of the volume rendered image volume. Looks like this with depth peeling on:
(The tube should disappear from view as it enters the nose, hidden by the rendered image volume, as in the very first image attached above for the fully opaque image)
So, this changes, but does not resolve the issue. Thanks for the response, I very much appreciate it.