MRI Risks, Side Effects and Red Flags to Watch For
The real risks of MRI, from implants and metal to contrast dye and kidney function, plus warning signs of an unsafe or overpriced provider.
MRI is generally very safe because it uses a strong magnetic field and radio waves instead of ionizing radiation. The real risks are few and mostly preventable: metal objects or implants that are not properly screened, rare reactions to gadolinium contrast, kidney problems in people who receive certain contrast agents, burns or heating from improper positioning, hearing damage without earplugs, and anxiety in the tube. A center that screens carefully removes most of these risks. This guide explains each risk, who is more exposed, and the red flags that should make you reconsider a provider.
The magnet and metal
The magnetic field is always on, even when no scan is running. Ferromagnetic objects can be pulled toward it with force. This is why every patient and visitor is screened and why metal items stay out of the scan room.
Implants and devices. Many are safe to scan: most joint replacements, many stents, most surgical plates and screws. Others are labeled "MR conditional," meaning the scan is safe only under specific conditions, such as a particular field strength or time limit. A few devices are unsafe. Cardiac pacemakers and defibrillators, cochlear implants, neurostimulators and some older aneurysm clips need special review. Bring the device card or the surgical record, and tell the center the manufacturer, model and date if you know it.
Metal fragments. Metal in the eye from grinding or welding, or bullet and shrapnel fragments, can move or heat. If you have had such exposure, say so; the center may require an X-ray before the scan.
Tattoos and permanent makeup. Some pigments contain metal and can warm or tingle. Serious burns are rare, but report any heat or burning during the scan immediately.
Heating and burns
Radio waves can warm tissue slightly. Burns are uncommon and usually come from skin-to-skin contact loops, conductive clothing or cables. Technologists use padding and positioning to prevent this. Wear what they give you, and always tell them if you feel warmth.
Noise and hearing
MRI scanners can exceed 100 decibels during some sequences. Earplugs or headphones are standard and should be used. Ask for them if they are not offered.
Contrast agents: gadolinium
Many scans do not need contrast. When one does, a gadolinium-based agent is injected into a vein.
- Allergic-type reactions are uncommon and usually mild, such as itching or hives. Severe reactions are rare. Tell the staff about prior reactions to contrast.
- Nephrogenic systemic fibrosis (NSF) is a rare, serious condition that has been linked to certain older gadolinium agents in people with severe kidney disease. Newer, more stable agents carry a much lower risk, and centers screen for kidney function in at-risk patients. Tell the staff about kidney disease, dialysis or a history of kidney problems.
- Gadolinium retention. Small amounts of gadolinium can remain in the body, including the brain, after contrast MRI. The FDA has studied this and has not identified harm in patients with normal kidney function, but it advises considering this when choosing repeat contrast scans. Ask your doctor whether contrast is truly needed.
- Pregnancy. Contrast is generally avoided in pregnancy unless the benefit is essential. Tell the staff if you are or may be pregnant.
- Breastfeeding. Guidance generally says breastfeeding can continue after contrast, but discuss it with your doctor and the radiologist.
Sedation risks
Sedatives and anesthesia carry their own risks, such as drowsiness, breathing changes and drug interactions. They should be given only with appropriate monitoring and a staff trained to manage them. This is why higher-risk patients should be scanned in hospital settings.
Claustrophobia and anxiety
A meaningful minority of people feel anxious in the scanner. It is not dangerous, but it can cancel the scan and cost money. Options include wide-bore or open scanners, feet-first positioning, music, a coach and medication. Read open vs closed vs wide-bore MRI.
Incidental findings and over-testing
A scan can reveal findings that are common and harmless, such as disc bulges in people without back pain. Interpreting them correctly requires your doctor's clinical judgment, because acting on every finding can lead to more tests and expense. This is a larger issue for direct-to-consumer screening scans, where evidence of benefit in people without symptoms is limited, according to professional radiology societies, and a false alarm can trigger costly follow-up.
Red flags in a provider
| Red flag | Why it matters |
|---|---|
| No safety questionnaire or interview | Unscreened metal and devices are the main danger |
| Will not name the radiologist or credentials | Poor reading quality risk |
| Pushes extra scans or contrast not ordered | Revenue motive over clinical need |
| No written price or Good Faith Estimate | Likely billing trouble |
| Pressure to prepay a large sum or sign a blank financial form | Billing risk |
| No hearing protection offered | Safety lapse |
| Cannot explain emergency procedures | Unprepared for events |
| Claims a scan can "detect everything" or promises certainty | Marketing, not medicine |
| No accreditation and no explanation | Unknown quality controls |
Warning signs during the scan
Press the call button for: chest pain, trouble breathing, severe anxiety, burning or heating of the skin, a feeling of a metal object pulling, sudden dizziness, hives or swelling of the face or throat. The technologist can stop the scan and call for help.
Warning signs afterward
Call your doctor or the center if you develop hives, persistent nausea or swelling at the injection site, new pain, or any unexpected symptom after sedation. For severe breathing trouble, swelling of the face or throat or chest pain, call 911.
Worked example (illustrative)
A patient with a knee replacement says nothing about it at a center that has no questionnaire. Fortunately most knee replacements are MR conditional, but the technologist adjusts the protocol to reduce artifacts only if told. In a second case, a patient with a pacemaker visits a center without a cardiology program; the center should decline or refer to a hospital with protocols. The safe pattern in both cases is full disclosure and a center that asks.
When to consult a professional
Patients with pacemakers, defibrillators, neurostimulators, cochlear implants, severe kidney disease, pregnancy or a history of contrast reactions should speak to their doctor and the center's MRI safety staff before booking. The center's medical director or radiologist makes the safety decision.
Frequently asked questions
Is MRI safer than CT?
MRI does not use ionizing radiation, which CT does. Which test is appropriate depends on the clinical question.
Can I have an MRI with a pacemaker?
Some modern pacemakers are MR conditional and can be scanned under strict protocols at suitable facilities. Ask your cardiologist and the center.
Does contrast stay in my body?
Most is cleared by the kidneys within a day in people with normal kidney function. Trace retention can occur; discuss necessity with your doctor.
Is a tattoo a problem?
Usually not, but report it; metal-containing pigments may warm.
Sources
- U.S. Food and Drug Administration — MRI safety and gadolinium-based contrast agent information
- American College of Radiology — manual on MR safety and contrast media
- RadiologyInfo.org — patient safety information
- National Kidney Foundation — kidney health and contrast
