Your concern is a very common one. MRI
stands for magnetic resonance imaging. There is no ionizing radiation (the harmful kind) in MRI scans. Instead, the parts of your body that are being imaged are exposed to high magnetic fields. This strong magnetic field causes the electrons (negatively-charged particles) that are associated with the atoms that make up our bodies to align. Based on the magnetic echo that is sent back to the detector, an image is created that can determine types of tissue/fluids, etc.
MRI is generally considered safe for most people. People that have devices implanted (pacemakers, automatic implantable cardiac defibrillators, vagus nerve stimulators, intrathecal pumps) need to check with their doctor
to see if those devices are MR-safe. Additionally, people that have had surgical clips placed for abdominal, cardiac, or intracranial procedures need to see if they have MR-safe clips. Most recently implanted clips are MR-safe.
Finally, people that have been exposed to metal working (where microscopic pieces of metal could have been implanted in skin, eyes, etc.) and those that have street or prison tattoos (i.e., not tattoo parlor) should also be careful. The latter frequently have large amount of metals that vibrate in the magnetic field. get very hot, and can burn skin. The effect of MR on fetuses has not been studied, so most physicians try to limit MR exposure for pregnant women. There are no known long-term effects of MR.
Other things to be aware of include claustrophobia (the MRI scanner is a tube that you go in) and loud noises (the MR scanner is very loud - it sounds like a super loud washing machine). Most imaging centers provide ear plugs or headphones for patients to assist with this inconvenience.