I do wonder whether this was actually an effective way to look for them. Even with modern high resolution x-ray imaging it may be difficult to see the contrast between soft tissues and diamonds since they're both primarily carbon
bones show up well since they're high in calcium, which has a much higher atomic number. Same with gold.
I mean if everyone tells you "we have a machine that can see through skin and can check if you have hidden diamonds" that would probably stop any attempts at theft that way. Even if it doesn't actually see them. Also, diamonds out of the mine would be uncut, and probably easier to see.