This is the public/consumer arm of Medline (Medline-plus) and it may help with the x-ray/imaging questions. http://wwwindex.nlm.nih.gov http://www.nlm.nih.gov/medlineplus/diagnosticimaging.html Zim may really be the one to answer this one. Ultrasound is usually not used to see cartlidge, but I am not sure about the second level (?) ultrasound. Got to see blood flow through the heart with it when my sister was pregnant, but again do not recall much in the way of cartlidge. I guess you could target various tissue depths, but to get a fully 3-D picture I think you would need to be able to vary the frequency (again... I am dredging it up for a quick post) and I am not sure how adaptable ocean dwellers are at that. I think you may be looking at gross-er reflections than what each cartlidge area would look like inside another animal. Hope that helps. Dee
