MRI does not use radiation in the way most people mean when they ask this question. Unlike X-rays and CT scans, which use ionizing radiation that can damage DNA and slightly increase cancer risk over time, an MRI produces images using a powerful magnet and radio waves. Neither of these harms DNA or raises cancer risk.
That said, the word “radiation” has a broad scientific meaning, and radio waves are technically a form of non-ionizing electromagnetic radiation, the same type your cell phone emits. This is very different from the ionizing radiation in X-rays, and it’s worth understanding exactly what happens inside the machine.
How MRI Creates Images Without X-Rays
Your body is mostly water, and water molecules contain hydrogen atoms with a single proton at their core. An MRI machine generates a magnetic field thousands of times stronger than the Earth’s, which forces those protons to line up in a uniform direction. The machine then sends pulses of radiofrequency energy through your body, knocking the protons out of alignment. When the pulse stops, the protons snap back into place and release small amounts of energy as they do.
Sensors inside the machine detect that released energy. Different tissues, whether muscle, fat, bone marrow, or fluid, take different amounts of time for their protons to realign, and they release different amounts of energy in the process. The MRI’s computer translates those differences into detailed cross-sectional images. The entire process involves no X-rays and no ionizing radiation at any point.
MRI vs. CT: The Radiation Difference
The confusion between MRI and CT scans is understandable because both produce detailed internal images and both involve lying inside a large machine. But their technology is fundamentally different. A CT scan is essentially a series of X-rays taken from many angles, and it delivers a meaningful dose of ionizing radiation. A single chest CT exposes you to about 7 millisieverts, roughly 70 times the dose of a standard chest X-ray.
MRI delivers zero millisieverts. It simply doesn’t appear on radiation dose charts because there’s no ionizing radiation to measure. This is one reason doctors prefer MRI when a patient needs repeated imaging over time, particularly for monitoring brain conditions, joint injuries, or soft tissue problems. You can have multiple MRI scans without any cumulative radiation exposure building up.
What MRI Risks Actually Exist
The absence of ionizing radiation doesn’t mean MRI is entirely without considerations. The strong magnetic field is the primary safety concern, and it’s the reason you’ll be asked detailed screening questions before every scan.
Ferromagnetic metal inside your body can be moved or heated by the magnetic field. Absolute contraindications include metallic foreign bodies in the eye (which could shift and damage surrounding tissue), certain implanted cardiac pacing leads (where radiofrequency pulses can induce electrical currents and cause burns), insulin pumps (both external and implanted types must be removed), and specific implanted devices with magnetic components. Even something as specialized as a contact lens designed to measure eye pressure continuously can cause severe burns inside the MRI environment.
If there’s any question about metal fragments in your body, especially near the eyes, a screening CT of the eye sockets may be done beforehand to confirm it’s safe to proceed. Most modern joint replacements, dental fillings, and surgical hardware are MRI-compatible, but the imaging team will verify each case individually.
MRI Contrast Agents and Their Risks
Some MRI scans require an injection of a contrast agent to make certain tissues or blood vessels stand out more clearly. The most common type is gadolinium-based. This is not radiation either, but it does carry its own set of risks worth knowing about.
Common side effects are mild: a warm or cold sensation at the injection site, headache, or nausea. More serious reactions like rash, hives, or difficulty breathing are possible but uncommon. The bigger concern involves people with kidney problems. Gadolinium can cause a condition affecting the skin, muscles, and other organs, with symptoms including skin hardening, joint stiffness, and deep bone pain. People over 60 or those with diabetes, high blood pressure, or kidney disease should make sure their doctor knows before contrast is ordered.
Gadolinium can also remain in small amounts in the brain, bones, and skin for months or even years after injection. The long-term significance of this retention is still being studied, but it’s one reason contrast is only used when it will meaningfully change the diagnostic outcome.
MRI Safety During Pregnancy
Because MRI involves no ionizing radiation, the American College of Obstetricians and Gynecologists considers it one of the preferred imaging options during pregnancy, alongside ultrasound. There are no precautions or contraindications specific to pregnant women, and no trimester is considered riskier than another.
Theoretical concerns have been raised about tissue heating, acoustic damage to the fetus, and effects on fetal development, but no published human studies have documented actual harm, and most animal studies show no risk. Tissue heating from the scanner is proportional to how close the tissue is to the scanner’s surface, making it negligible near the uterus. Studies monitoring fetal hearing after prenatal MRI have found no acoustic injuries.
Gadolinium contrast during pregnancy is a different matter. One large study found that pregnancies exposed to gadolinium had higher rates of certain skin conditions in the newborn and a significantly increased risk of stillbirth and neonatal death compared to unexposed pregnancies. For this reason, gadolinium is reserved for situations where the diagnostic benefit clearly outweighs the potential risk to the fetus. For breastfeeding mothers, however, gadolinium does not require any interruption of nursing.
Why MRI Is Preferred for Children
Children are more sensitive to ionizing radiation than adults because their cells are dividing rapidly and they have more years ahead in which radiation-related damage could develop into cancer. The National Cancer Institute specifically recommends that when imaging can be accomplished with ultrasound or MRI instead of CT, those non-ionizing options should be used.
The practical challenge with pediatric MRI is that the scan requires the patient to hold very still for extended periods, which can be difficult for young children. Sedation or anesthesia is sometimes needed, and that carries its own small risks. But from a radiation standpoint, MRI adds zero exposure, making it the safer long-term choice when it can provide the diagnostic information needed.