An MRI scan is painless, requires no needles (unless contrast dye is needed), and typically takes 25 to 45 minutes depending on the body part being scanned. But the experience can feel unfamiliar, from the loud knocking sounds to lying still inside a narrow tube. Here’s a detailed walkthrough so nothing catches you off guard.
How the Machine Creates Images
An MRI uses a powerful magnet and radio waves instead of radiation. Your body is mostly water, and water molecules contain tiny particles called protons that behave like miniature magnets. When you enter the machine, the magnetic field lines up these protons so they all point in the same direction. The machine then sends a pulse of radio waves through your body, knocking the protons out of alignment. As they snap back into place, they release signals that the machine detects and translates into detailed images of your organs, joints, and soft tissues.
Different types of tissue (healthy muscle vs. a torn ligament, for example) release slightly different signals as the protons relax. That difference is what gives MRI its remarkable ability to distinguish between tissues, making it especially useful for brains, spines, joints, and abdominal organs.
Before You Arrive
Most MRI scans require no special preparation. You can eat, drink, and take your medications normally. The exception is abdominal, pelvic, and liver scans, which typically require you to fast for about four hours beforehand. You can still take your usual medications with small sips of water during that fasting window.
Your imaging center will send you a screening questionnaire about metal in or on your body. This is the single most important safety step. Certain implants are not compatible with MRI at all, including most pacemakers and cochlear implants. Other implants, like hip replacements, stents, or surgical hardware in the skull, need to be reviewed and approved before you can safely enter the room. If you have any implanted device, bring documentation (such as an implant card) so the team can verify it’s MRI-safe.
What to Remove and What to Wear
You’ll be asked to remove all metallic items before entering the scan room: jewelry, watches, hairpins, bobby pins, hearing aids, belts, wallets, phones, keys, and orthotics. Most facilities provide a locker and a hospital gown or scrubs to change into.
If you’re told you can wear your own clothes, choose carefully. Many athletic fabrics now contain invisible silver microfibers woven into the material for odor control. These metallic threads can interact with the machine’s energy and cause skin burns. A case published in the American Journal of Neuroradiology documented second-degree burns from a shirt with silver-impregnated fabric that was invisible to the naked eye. In fact, about 70% of MRI-related complications reported to the FDA involve thermal burns. The safest option is to wear the gown provided or plain cotton clothing with no metallic components, including in the zipper, underwire, or decorative elements.
The Scan Room and Getting Positioned
The MRI scanner looks like a large, hollow tube. A standard machine has an opening about 60 centimeters (roughly 24 inches) wide. Wide-bore machines, which are increasingly common, open up to about 70 centimeters. You’ll lie on a padded table that slides into the center of the tube. Depending on the body part being scanned, the technologist may place a plastic device called a coil over or around the area. This is just an antenna that helps the machine pick up better signals.
For brain and head scans, the coil fits around your head like a cage. It doesn’t touch your face, but it does restrict your view. For knee or wrist scans, a smaller coil wraps around the joint. Once you’re positioned, the technologist will leave the room but stay in constant contact through an intercom and a window. You’ll usually get a squeeze ball or call button to signal the team if you need to stop at any point.
What It Sounds and Feels Like
The machine is loud. Depending on the type of scan and the strength of the magnet, noise levels range from about 82 decibels (comparable to heavy traffic) up to 115 decibels or more on high-powered 3-Tesla machines. Some sequences at 3-Tesla have been measured above 126 decibels on a linear scale. For perspective, a rock concert is around 110 decibels.
You’ll hear a series of loud knocking, banging, and buzzing sounds. Each sequence sounds different, and there are quiet gaps between them. You will always be given earplugs, headphones, or both. Properly fitted earplugs reduce noise by 10 to 30 decibels, which brings even the loudest sequences down to a manageable level. Many centers also pipe music or audio through the headphones.
You won’t feel the magnetic field or the radio waves. The table may vibrate slightly during certain sequences, and some people notice mild warmth in the area being scanned. Neither sensation is cause for concern. The most challenging part for most people is simply lying still.
How Long It Takes
Brain and spine scans typically last about 45 minutes. Joint scans (knee, ankle, hip, wrist, elbow) generally run 25 to 45 minutes, with the exact time depending on the size of the area. Scanning a full thigh bone, for instance, takes longer than a routine knee. If your scan requires contrast dye, add roughly 15 minutes to those estimates.
You’ll need to hold still throughout. Even small movements blur the images and may require the technologist to repeat a sequence, adding time. Between sequences, you can usually swallow or make small adjustments, and the technologist will tell you through the intercom when those brief breaks are happening.
Contrast Dye
Some scans require an injection of a contrast agent called gadolinium, which highlights blood vessels, inflammation, and certain abnormalities that might not show up clearly otherwise. The injection goes into a vein in your arm, usually about halfway through the scan. You might feel a brief coolness or a metallic taste, but both pass quickly.
Adverse reactions to gadolinium are rare. In a large European registry of nearly 18,000 patients, only 0.17% experienced any reaction at all, and every single one was classified as mild (things like brief nausea, hives, or a headache). Before receiving contrast, you’ll be asked about kidney problems, since the body clears gadolinium through the kidneys. If your kidney function is significantly reduced, your doctor may choose a different imaging approach.
If You’re Claustrophobic
Feeling anxious about enclosed spaces is one of the most common concerns, and imaging centers deal with it every day. Strategies that help include keeping your eyes closed from the moment you lie down, using the headphones to focus on music or a podcast, and asking the technologist to tell you how long each sequence will take so you can mentally count down. Some people find it helps to enter the machine feet-first (possible for lower body scans) so their head stays near the opening.
If you know you’re claustrophobic, call your referring doctor’s office before your appointment. A mild sedative taken about an hour before the scan can make a significant difference, but you’ll need someone to drive you home afterward. You can also ask whether a wide-bore machine is available at your facility, since that extra 10 centimeters of space is noticeable.
MRI During Pregnancy
MRI is considered safe during pregnancy. Unlike CT scans or X-rays, it uses no ionizing radiation. The American College of Obstetricians and Gynecologists states there are no precautions or contraindications specific to pregnant women, though it notes that MRI should still be used only when it’s expected to answer a meaningful clinical question. Theoretical concerns about tissue heating and acoustic effects on the fetus have not been supported by evidence of actual harm.
Gadolinium contrast is a different matter. Because it crosses the placenta and enters fetal circulation, it’s used during pregnancy only when the diagnostic benefit clearly outweighs the uncertainty. If you’re breastfeeding, however, there’s no need to interrupt nursing after receiving gadolinium.
Getting Your Results
The technologist who performs your scan cannot share results with you. The images go to a radiologist, a doctor who specializes in reading medical imaging, who writes a formal report and sends it to the physician who ordered your scan. Most results are available within a few business days, though urgent or emergency scans are read much faster. Your referring doctor’s office will typically call you or make the report available through a patient portal. If you haven’t heard anything within a week, it’s reasonable to call and ask.