An MRI scan is a painless imaging procedure that typically takes 25 to 60 minutes, during which you lie still inside a large tube-shaped machine while powerful magnets and radio waves create detailed pictures of the inside of your body. No radiation is involved. Here’s what happens before, during, and after the scan.
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 slide into an MRI scanner, its powerful magnet (typically 1.5 or 3 Tesla, thousands of times stronger than a refrigerator magnet) forces those protons to line up in roughly the same direction, creating a faint but detectable magnetic signal.
The machine then sends short bursts of radio waves tuned to the exact spinning frequency of those protons. This knocks them out of alignment and transfers energy to them. When the radio pulse stops, the protons snap back into line and release that energy as a signal. Different tissues (fat, muscle, bone marrow, fluid) release energy at different rates, and the scanner’s receivers pick up those differences. A computer translates millions of these signals into cross-sectional images with remarkable soft-tissue detail, far more than X-rays or CT scans can show.
What Happens Before the Scan
You’ll complete a safety screening questionnaire, and this step is non-negotiable. The magnet is always on, so anything ferromagnetic in or on your body is a potential hazard. Staff will ask whether you have a cardiac pacemaker, implantable defibrillator, cochlear implant, neurostimulator, drug infusion pump, aneurysm clips, metal fragments from prior injuries (bullets, shrapnel), or any implant held in place by a magnet. These are absolute contraindications that can prevent the scan entirely or require clearance from an MRI safety officer.
You’ll also be asked to remove all metallic objects: jewelry, watches, hair pins, belt buckles, coins, credit cards, body piercings, hearing aids, and dentures. Medication patches (like nicotine patches) need to come off too, because some contain metallic foil that can heat up. Many facilities provide a gown and a locker for your belongings.
Getting Positioned on the Table
A technologist will have you lie on a padded table, almost always on your back. Depending on which body part is being scanned, they’ll place a specialized receiver coil around or near it. Think of the coil as an antenna that picks up the signals from your tissue. A brain MRI uses a cage-like coil that fits around your head, with your chin tilted slightly upward. A knee scan uses a cylindrical coil your knee slides into with a slight 15-degree bend. Shoulder, ankle, wrist, and spine each have their own coil shapes and positioning requirements.
Proper positioning matters. If the coil isn’t centered on the area of interest, the images lose quality, and the scan may need to be repeated. The technologist will use laser alignment lights or touch sensors to get this right, and they may tuck foam pads around you to help you stay still.
What It Feels Like Inside the Scanner
The table slides into the bore of the machine, which is essentially a horizontal tube. A traditional MRI bore is about 60 centimeters (roughly 24 inches) across. Wide-bore machines offer about 70 centimeters, and that extra 10 centimeters makes a noticeable difference if tight spaces bother you. Open MRI systems, which have open sides, are another option, though they often produce lower-resolution images.
The loudest part of the experience is the noise. MRI scanners produce rapid banging, buzzing, and clicking sounds as the magnetic field gradients switch on and off. At 3 Tesla, time-averaged sound levels typically exceed 95 decibels and can peak above 105 decibels, comparable to standing near a jackhammer. The FDA caps the maximum allowable sound at 140 decibels. You’ll be given earplugs or padded headphones before the scan begins, which reduce noise by 10 to 30 decibels, and many facilities play music through the headphones.
You won’t feel the magnetic field or radio waves. The only physical sensation some people notice is mild warmth in the area being scanned. You’ll have a call button or squeeze ball to signal the technologist at any time, and they can talk to you through an intercom between sequences.
When Contrast Is Used
Some scans require a gadolinium-based contrast agent to make certain tissues, blood vessels, or abnormalities show up more clearly. If your scan calls for contrast, a small IV catheter will be placed in your hand or arm vein before or partway through the exam. The contrast is injected through the IV, and you may feel a brief cool sensation as it enters.
Gadolinium works by altering how nearby water molecules behave in the magnetic field, causing those tissues to appear brighter on the images. It’s commonly used when looking for tumors, inflammation, or blood vessel problems. Adding contrast typically extends the total scan time by about 15 minutes.
How Long the Scan Takes
Scan duration depends on the body part and how many image sequences the radiologist has ordered:
- Brain or spine: about 45 minutes
- Abdomen or pelvis: 45 to 60 minutes
- Knee, ankle, hip, elbow, or wrist: 25 to 45 minutes
- Specialty exams (cardiac MRI, full-body staging): up to 2 hours
Each scan consists of multiple sequences, and each sequence captures a different type of tissue contrast. Between sequences, the machine goes quiet for a few seconds. The technologist will often tell you how many minutes remain in each sequence so you know what to expect. Staying still throughout is critical, because even small movements blur the images and may require repeating a sequence.
After the Scan
Once the final sequence finishes, the table slides out, the coil is removed, and you can get up. If contrast was used, the IV is removed. There’s no recovery period. You can eat, drive, and return to normal activities immediately.
A radiologist reviews the images and writes a report for the doctor who ordered the scan. Turnaround time varies by institution and urgency. Emergency or “STAT” orders are typically read within an hour. Routine outpatient scans are often reported within 24 hours, though some facilities take a few business days. Your ordering physician will contact you with the results or discuss them at a follow-up appointment. In many health systems, images and reports also become available through an online patient portal.