MRI scans are not dangerous for the vast majority of people. Unlike CT scans and X-rays, an MRI uses no ionizing radiation at all. It works by passing radio waves through your body inside a powerful magnetic field, causing water molecules in your tissues to produce signals that create detailed images. There is no known cumulative risk from repeat scans, and no recovery time afterward.
That said, the MRI environment does carry specific hazards, mostly related to the magnet itself and, in some cases, the contrast dye used to enhance images. Understanding these risks helps explain why the screening process before your scan matters so much.
The Magnet Is the Main Safety Concern
An MRI magnet is extraordinarily powerful, and it’s always on, even when no scan is running. Any ferromagnetic object (anything a regular magnet would stick to) brought into the room can be pulled toward the scanner at high speed. This is called the projectile effect, and it’s the single most serious physical danger in an MRI suite. The attractive force is strongest right at the opening of the scanner bore.
Projectile incidents account for roughly 5 to 9 percent of all reported MRI adverse events. Wheelchairs and stretchers are the most common culprits, involved in about 26 percent of projectile cases reported to the FDA over a ten-year review period. Gas cylinders are another frequent offender. In 2001, a child died after an oxygen tank was pulled into the scanner and struck him. Smaller metal objects like surgical instruments, scissors, or even hairpins can also become dangerous projectiles.
This is why MRI facilities follow strict zone-based screening. You’ll be asked to fill out a detailed questionnaire, change into a gown, and pass through a ferromagnetic detection checkpoint before entering the scanner room. Staff go through the same screening. The American College of Radiology recommends at least two separate screenings before anyone enters the room where the magnet is housed.
Metal Implants and Medical Devices
If you have metal in your body, whether from surgery, an implant, or even old shrapnel, it needs to be evaluated before you can safely have an MRI. The FDA uses three labeling categories for medical devices:
- MR Safe: The device contains no metallic, magnetic, or electrically conductive materials and poses no known risk in any MRI environment.
- MR Conditional: The device has been tested and shown to be safe under specific MRI conditions, such as a certain magnet strength or scan duration.
- MR Unsafe: The device poses unacceptable risks and should not enter the MRI room.
Older pacemakers and certain cochlear implants fall into the MR Unsafe category, though many newer cardiac devices are now MR Conditional. The key is knowing exactly what device you have and what conditions were tested. Your MRI team will look up the specific model and manufacturer before clearing you for the scan. If you aren’t sure what’s in your body, tell the technologist. They’d rather delay a scan than take a chance.
Beyond the projectile risk, metal implants can also heat up during scanning because the radiofrequency energy used to generate images can induce electrical currents in conductive materials. This heating effect is regulated by the FDA, which sets limits on how much energy the scanner can deposit into tissue: no more than 4 watts per kilogram for whole-body scans and 3.2 watts per kilogram for head scans, averaged over several minutes.
Contrast Dye and Kidney Risk
Not every MRI requires contrast, but when it does, you’ll receive an injection of a gadolinium-based contrast agent through an IV. For most people, this is safe and uneventful. Mild side effects like a brief cool sensation at the injection site or a metallic taste are common and pass quickly.
The serious concern with gadolinium is a rare condition called nephrogenic systemic fibrosis (NSF), which causes thickening and hardening of the skin and connective tissues. It occurs almost exclusively in people with severe kidney disease. When older, higher-risk contrast agents were used, the incidence was about 36.5 cases per 100,000 gadolinium-enhanced MRIs. Newer contrast agents have essentially eliminated this risk: systematic reviews have found no biopsy-proven cases of NSF among patients receiving the newer formulations, putting the estimated risk below 0.07 percent.
Because of this, your kidney function will be checked before you receive contrast if there’s any reason to suspect it might be impaired. Current guidelines recommend avoiding gadolinium contrast in patients whose estimated kidney filtration rate (eGFR) falls below 30. If contrast is still necessary in someone with reduced kidney function, the lowest-risk agents are used with extra caution.
Gadolinium Retention in the Brain
In 2017, the FDA issued a safety communication noting that small amounts of gadolinium can remain in the brain and other tissues for months or years after contrast-enhanced MRIs. This finding prompted understandable concern, but the FDA has also stated that it has identified no harmful effects from this retention to date. Monitoring is ongoing, and the finding is one reason doctors try to use contrast only when the diagnostic benefit clearly justifies it.
Noise Levels Inside the Scanner
MRI machines are loud. The rapid switching of gradient coils during scanning produces repetitive banging, buzzing, and clicking that can be startling if you’re not prepared. Without ear protection, these noise levels can cause both temporary and, in some cases, permanent hearing changes.
Every MRI facility provides earplugs, and many also offer headphones that can play music. Together, these provide at least 30 decibels of noise suppression. The rule at most centers is straightforward: no earplugs, no scan. If you’re given ear protection and it falls out or feels loose, let the technologist know before the scan starts.
Claustrophobia and Scan Anxiety
About 2.3 percent of all patients scheduled for an MRI experience enough claustrophobia that they either cannot complete the scan or need sedation. With over 80 million MRI procedures performed worldwide each year, that translates to roughly 2 million scans that are cut short or canceled because of anxiety. This isn’t a trivial problem, and it doesn’t mean something is wrong with you. The scanner bore is narrow, the noise is intense, and you need to stay still for 20 to 60 minutes depending on the study.
Newer wide-bore, short-tunnel scanners have made a measurable difference. A study of more than 55,000 patients found that a scanner designed with a wider opening, shorter tunnel, and 97 percent noise reduction cut claustrophobic reactions by a factor of three. If you know you’re prone to claustrophobia, ask whether your facility has a wide-bore scanner, or whether an open MRI is an option for your particular exam. Mild sedation is also available and commonly used.
Pregnancy and MRI
MRI is generally preferred over CT during pregnancy because it doesn’t involve radiation. There is no confirmed evidence that the magnetic fields or radio waves harm a developing fetus. However, gadolinium contrast is typically avoided during pregnancy because it can cross the placenta, and its effects on the fetus haven’t been fully established. When imaging is needed during pregnancy, a non-contrast MRI is the usual approach.
What Makes MRI Safer Than Many Alternatives
The absence of ionizing radiation is the single biggest safety advantage MRI holds over CT scans and X-rays. Ionizing radiation carries a small but real cumulative cancer risk, which is why doctors track how many CT scans a patient has had over time. With MRI, there is no radiation dose to accumulate, so repeated scans don’t carry that same long-term concern. For soft tissue imaging, brain scans, spinal evaluations, and joint injuries, MRI often provides superior detail without any radiation trade-off.
The real risks of MRI are almost entirely preventable: metal screening catches projectile hazards, kidney function tests identify patients who shouldn’t receive contrast, and ear protection eliminates noise-related injury. When the screening process is followed correctly, MRI is one of the safest and most informative imaging tools available.