That they are. Fun fact, at least as of a few years ago when I was learning about it, magnetic field intensities are measured in teslas in the SI unit system. These are named after Tesla himself (who pronounced his name “Tezla”). Those superpowerful neodymium-iron-boron magnets have a field intensity near their pole surfaces of about 1 tesla (1 T). Medical MRI machines generally have at least this field intensity, and perhaps more. Somebody here mentioned a 3 T machine being specified for their imaging, for example. As a rule of thumb, an MRI machine costs about $1,000,000 per tesla.
I think it’s more subtle than this. Ferromagnetic substances, like iron, will feel forces inside the powerful magnetic field. Folks worry about metal fragments inside the eye, and some implants like aneurism clips, for fear they’ll jump about scrambling soft tissue. Nonferromagnetic substances may still move about a bit, because of their interactions with the variation in the magnetic field. For example, my gold wedding band, which is a closed loop of conductor like a winding in an induction motor, vibrates. Further back, they would tell me the ring had to come off, but in more recent years they said it was OK (I take it off anyway because I dislike the vibrations). Also, metals confuse the signal, so there are image artifacts around pieces of metal. I have fixation plates in my neck, and both MRI scans and CT scans get image artifacts around the plates, though the effect of the metal is different so the two kinds of scans get different image artifacts. So, the rules about metal are sometimes subject to some judgement (though steel in the eyes or brains, I bet, are non-negotiably forbidden).
It was gadolinium, a fascinating elemental metal that looks about like steel. It’s ferromagnetic below its Curie point temperature, and not so above it (this is true of all ferromagnetic substances). But, interestingly, its Curie point temperature is about room temperature. You can drop a piece in your icewater and then lift it with a magnet, then warm it in your hand and the magnet won’t pull it anymore. Curie point temperatures are usually higher – the chromium oxide they make recording tapes out of is about 150 C, and nickel about 350 (iirc). And you were given some salt of gadolinium, not the metal itself.
I was just talking to a friend about this yesterday. I find it difficult to be on my back because I have chronic bronchitis and a bad post nasal drip, and it is hard for me to manage my airway that way without frequent coughing and forceful exhalations. I was wondering if one could choose to be on one’s front. She said that she had MRIs lying on her front, as part of her breast cancer experience. Turns out she HAD TO be on her front. So I don’t know if it’s ever optional for the patient to lie on whichever they prefer. I do have more MRIs coming up (I’ve probably had a dozen or so) – any insight here would be welcome!
Yeah, gadolidium I meant.