During an MRI, you lie still inside a large tube-shaped magnet while the machine uses powerful magnetic fields and radio waves to create detailed images of your internal organs, bones, and soft tissues. The process is painless, involves no radiation, and typically takes 25 to 60 minutes depending on the body part being scanned. Here’s what to expect from start to finish.
How the Machine Creates Images
Your body is about 70 percent water, and every water molecule contains hydrogen atoms. Each hydrogen atom has a single proton that acts like a tiny spinning magnet. Normally, these protons point in random directions. When you enter the MRI scanner, its powerful magnetic field forces the protons to line up in roughly the same orientation, like compass needles pointing north.
The machine then sends short bursts of radio waves into your body. These pulses knock the aligned protons out of position. When the radio waves stop, the protons snap back into alignment, and as they do, they release energy. The scanner detects that released energy and uses it to build a picture. Different types of tissue (muscle, fat, bone marrow, fluid) release energy at different rates, which is what creates contrast between structures in the final image. No radiation is involved at any point.
Before You Enter the Room
The MRI magnet is always on, so the safety screening starts well before you get near the scanner. You’ll fill out a questionnaire about any metal in or on your body. The magnetic field can move, heat, or damage metallic objects, which makes certain implants dangerous in the scanner. Absolute contraindications include most older pacemakers and defibrillators, cochlear implants, implantable drug infusion pumps, cerebral aneurysm clips, and metallic foreign bodies (particularly in the eyes). If you have a history of facial trauma involving metal fragments or unprotected welding work, you may need an orbital X-ray to rule out tiny metallic pieces near your eyes before the scan can proceed.
Newer “MRI-conditional” pacemakers and defibrillators are now widely available, but scans with these devices require dedicated scheduling and monitoring by a cardiac technician. Body piercings, hearing aids, prosthetic limbs with metal components, and even some dental implants need to be removed or evaluated.
You’ll be asked to change into a hospital gown or wear loose, comfortable clothing with no metal. That means no belts, underwire bras, jewelry, zippers, or buttons. For abdominal or pelvic scans, you may be asked to stop eating and drinking four hours beforehand. Prostate MRIs typically require fasting for three hours. Most other scans have no fasting requirement.
Getting Positioned in the Scanner
The technologist will have you lie on a padded table that slides into the scanner bore, a tube roughly two feet in diameter. Depending on the body part being imaged, a specialized receiver coil (a plastic frame that improves image quality) may be placed over or around the area of interest. For a brain scan, this looks like a cage that fits around your head. For a knee scan, your knee goes into a smaller cradle-like device.
You’ll get a squeeze bulb to hold throughout the exam. Pressing it triggers an alarm that immediately alerts the technologist. You can also communicate through a built-in intercom system. Many facilities offer a leg cushion for back support, a warm blanket, and prism glasses that let you see out of the bore toward your feet, which can make the experience feel less enclosed.
What It Sounds and Feels Like
The scanner is loud. Sound levels routinely exceed 95 decibels and can spike above 105 decibels on higher-strength machines, comparable to standing near a running chainsaw. The noise comes from rapid vibrations in the scanner’s internal coils and sounds like a series of loud knocking, buzzing, and thumping patterns that change as the machine runs different imaging sequences. You’ll be given earplugs, headphones, or both. Well-fitting earplugs alone reduce noise by 10 to 30 decibels, bringing the sound within safe exposure limits. Many centers play music through the headphones as well.
You won’t feel the magnetic field or the radio waves. The table may vibrate slightly during certain sequences, and some people notice a mild warming sensation in the area being scanned, but neither is painful. The hardest part for most people is simply lying still. Any movement blurs the images and may require repeating a sequence.
How Long the Scan Takes
Scan times vary quite a bit by body part. Joint scans (knee, ankle, wrist, elbow, hip) are among the shortest, typically 25 to 45 minutes. Brain and spine exams average about 45 minutes. Abdominal and pelvic scans run 45 to 60 minutes. Breast imaging takes 45 minutes to an hour. Cardiac MRIs are the longest, often running 90 minutes to two hours because the scanner has to account for heartbeat and breathing motion.
If your scan includes contrast, add about 15 minutes. The technologist will enter the room partway through the exam to inject the contrast agent into a vein in your arm, then continue scanning.
Contrast Injections
Not every MRI requires contrast, but when it does, the agent used is typically gadolinium-based. Gadolinium is a metallic element that changes how nearby water molecules behave in the magnetic field, making certain tissues (like tumors, inflammation, or blood vessels) stand out more clearly. The initial images are always taken without contrast so the radiologist can compare before and after.
The injection feels like a standard blood draw. The most common side effects are minor: brief coolness or discomfort at the injection site, mild nausea, a headache, or slight dizziness. Serious allergic reactions are rare. Gadolinium-based contrast is different from the iodine-based dye used in CT scans, so an allergy to CT contrast doesn’t necessarily mean you’ll react to MRI contrast.
Managing Claustrophobia and Anxiety
Up to 10 percent of patients cannot complete an MRI due to claustrophobia triggered by the narrow bore, the loud noise, or the need to hold still for an extended period. If you’re prone to anxiety in tight spaces, you have several options.
Mild to moderate sedation with an oral anti-anxiety medication is the most common approach for adults. Intranasal or oral midazolam (a fast-acting sedative) has been shown in controlled studies to significantly reduce MRI-related anxiety and improve image quality. If you’re sedated, you’ll need someone to drive you home. Some facilities offer open MRI machines with wider bores or open sides, though these use weaker magnets and may not produce images as detailed as a standard closed scanner.
For young children, patients with severe developmental disabilities, or anyone who cannot stay still, deeper sedation or general anesthesia may be necessary. In adults, general anesthesia for an MRI is uncommon and generally reserved for extreme cases like uncontrollable agitation or severe psychiatric conditions.
After the Scan
Once the final images are captured, the table slides out. If you had contrast, the IV line is removed. If you weren’t sedated, there’s no recovery period. You can eat, drink, and drive immediately. The images go to a radiologist for interpretation, and results are typically sent to your ordering physician within a few business days, though urgent findings may be communicated the same day.