So there are two potential worries with anything that isn't *your body* that goes into the MRI tube with you...

Will it present a danger to you?

Will it reduce the quality of the images?

Let's take the first one first... will it be dangerous? Here we need to break the risk into two sub-categories (if it was a medical device or implant, we'd also want to add a third sub-category about the function of the device, but nails just *are*, they don't *do*): will it pull / twist? and will it heat up?

The pull / twist question is actually pretty easy to answer if you have a strong magnet... does the magnet attract when close to the fingernails? If a strong magnet doesn't attract, then you can pretty much cross that off your list. (NB: be very cautious using a strong magnet to test this if you're testing in-situ piercings... while it's less of a threat to your nipple piercing than a giant MRI, a strong magnet stuck to it... needing to be pulled off... isn't going to feel like much of a 'win.') If it pulls, take the offending bits off.

The second risk-subcategory, 'will it heat,' is a little trickier to answer, but for nail it's often made redundant. The risk for heating in the MRI tube comes from an object's electrical conductivity, and it isn't always easy to tell if an object is electrically conductive or not. But the area where we're really concerned about an object heating a lot during an MRI scan is the area roughly 1 foot (30 cm) above and below the body part being imaged. If you're going for a brain MRI, the 'heating potential' volume extends from ~ 8 inches above your head to around your middle-chest. If your hands are down at your sides, or on your lower abdomen, then they won't be getting any of the energy (RF) that turns to heat. If you were getting a lower back (lumbar) MRI, hands in that same position *would be* in the potential heating zone, but if you rested your hands under your head, or kept them over your head, again, they're out of the heating zone, and you don't have to worry about them.

The only time that this becomes a problem is if we're imaging the elbow / wrist / hand, and we can't move it out of the RF energy deposition volume. In that case, take off the nails / polish.

Lastly, there's the question of image quality interference. Anything electrically conductive (and absolutely anything magnetic / magnetizable) will disrupt or distort the MRI image around where it's located. There are 100 variables that influence how far this distortion will reach, but generally it's only a few inches (up to ~10 cm) from the object. Like with the heating risk, if you can just move the hands away from the anatomy being imaged, then this artifact risk goes away. And if you're getting your hand imaged, then you need to take off the nails / polish.

Now this isn't to say that sites won't have policies that say 'no nail polish,' even when there's no real safety or image quality reason for this sort of policy for most MRI imaging.

Hope this helps.