okay, here's some of my thoughts:
1. it's an MRI. i'm not a doctor or anything, but it is a CROSS section (or it looks like it to me) which would be an MRI, not an x-ray or ultra-sound.
2. the images are of colleen. the recruiter said 20ish (can't remember exactly), colleen fits the bill. i think the main reason colleen's death was upsetting to the others was that she may have been pregnant. remember sun, shot her in the stomach. i think that means something.
3. maybe kate was dressed up in front of sawyer for them to "get it on". who knows, maybe they are trying to get her pregnant. maybe they tried to "inseminate" her with ben. we still don't know what all happened with ben/kate.
there are still a lot of things that could have happened. i mean, who's to say these mri images aren't completely fake just to get juliet on the island!