The receiver coil picks up the RF electromagnetic radiation produced by nuclear relaxation inside the subject.
2.
The RF electromagnetic radiation produced by nuclear relaxation inside the subject is true EM radiation ( radio waves ), and these leave the subject as RF radiation, but they are of such low power as to also not cause appreciable RF interference that can be picked up by nearby radio tuners ( in addition, MRI scanners are generally situated in metal mesh lined rooms which act as Faraday cages .)
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