You should try another logic perhaps, you know. Because I think you might be excessively worrying even after an X-ray.
Think about it: Would that stuff that you think is in your body be made of normal metal? Would anybody be that absolutely stupid, really? (Especially aliens, governments, secret organisations and whatever.)
Would they not rather choose a material or a special metal that will remain unaffected and undetected by common everyday devices, including an MRI? If it's undetectable, it won't react or be influenced by even an MRI.
Just imagine what extensive trouble it would be to have a person running around with common detectable metal in their body just in everyday life. That would make is impossible to keep it secret from normal people and especially from doctors.
There's, like, no chance that MRI will go wrong. Conspirational organisations aren't stupid or careless, seriously.
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Autism + ADHD
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The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it. Terry Pratchett