Magnetic metals can convert the radio-frequency pulses of an MRI machine into electricity. The burning sensation that would be felt at the site of the tattoo may be a result of electricity running through the tattoo or from the 'pull' exerted on the magnetic material in the tattoo.
I am unaware of any state laws requiring a technician to warn patients of a potential interaction between a tattoo and an MRI, so if you believe you may have a tattoo containing an iron oxide pigment, you need to bring this up with your physician.

