Image 6_2 looked good for me. I’ve used Segment Editor module’s Threshold effect to create surface and then Scissors effect to remove irrelevant parts and got this:
Scene file: download. This segmentation is usable for 3D printing.
After that, I’ve used Margin effect to grow the segmentation a bit and used it as mask in Mask Volume effect (this effect shows up if you install SegmentEditorExtraEffects extension) to blank out parts of the input volume that are outside the segmented region, and visualized result using Volume rendering module:
Scene file: download