The How and Why of Your MRI

You might be wondering how a giant magnet is going to create images of your insides. Or maybe you’re wondering why you have to do, wear, or disclose such specific and seemingly random things before your scan. I mean, permanent makeup? Really?

We wondered that, too! Here’s what we learned.

How does MRI work?

MRI, or magnetic resonance imaging, is used to scan everything from your brains to your veins. Since it’s noninvasive and doesn’t use any form of radiation, MRI is the imaging method of choice if you need a lot of scans or a lot of detail.

The magnet in the MRI makes the positively charged protons inside your atoms fall in line with the magnetic field around you. Then, a radio wave passes through the magnetic field and excites those protons, making them wiggle out of that tidy arrangement created by the magnetic field.

When the radio wave is removed and the protons fall back into line, the scanner records the amount of released energy and how long the protons take to fall back into place.  Every type of structure in your body – from bone to brain – has a specific combination of energy released and proton return time. That’s how the MRI scanner can differentiate between your internal structures.

How does an MRI scan feel?

You really shouldn’t feel much of anything from the scan itself, though you may feel a little stiff from lying in the same position for the duration of the scan.

Claustrophobic? If the idea of lying inside a big noisy magnetic tube makes you nervous, tell your doctor before you go. You might be prescribed a sedative to help with the anxiety.

Why do I have to change into scrubs or a hospital gown?

The magnetic field produced by the MRI machine is strong enough to hurl a wheelchair across the room. You don’t want to be attached to anything metal that might have a similar effect. You might be able to wear your own clothes if you don’t have any sort of metal in your clothing – even snazzy metallic threads – but odds are good you’ll be sporting hospital chic, just to be safe.

This is where we have to mention that you need to disclose any piercings, implantable medical devices like pacemakers, former bullet or shrapnel wounds, working with sheet metal – ANYTHING that could introduce metal to the body. Tell your tech up front so they can adjust accordingly. You really don’t want the magnet to find that piercing you forgot about.

Why do I have to disclose any tattoos or permanent makeup?

Believe it or not, some tattoo inks (even those used for permanent makeup) are made with magnetic components, like iron oxide. The atoms in those metallic compounds can distort the MRI image…or worse, cause burns or swelling to your skin.

Don’t panic – not every tattoo is affected, and tattoos don’t automatically disqualify you from getting an MRI. Oh, and this should probably go without saying, but if you start feeling anything burning during your MRI, you should let your tech know immediately.

Why do I get earplugs or earphones during the MRI?

Easy one. The MRI scanner thumps and whirs and can generally sound like the outside of a busy night club. Ear protection or music can help minimize the noise.

Why would I need an MRI with contrast? (embed link to procedure)

Basically, if your doctor says so. Contrast adjusts the magnetic properties of certain soft tissues so they stand out in the image.

How will I feel after my MRI?

You should feel pretty normal and ready to get back to the daily grind, unless you had a sedative, in which case you should get someone to drive you home so you can sleep it off. If you had contrast, just keep an eye out for any signs of allergic reaction.

Unless your doctor tells you otherwise, go be free and rest assured that your MRI is giving your doctor all sorts of inside information…get it? Inside information? Thanks, we’ll be here all week.

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Sources:

http://www.mayoclinic.org/tests-procedures/mri/basics/what-you-can-expect/prc-20012903

http://www.hopkinsmedicine.org/healthlibrary/test_procedures/orthopaedic/magnetic_resonance_imaging_mri_of_the_bones_joints_and_soft_tissues_92,p07652/#MRI_prep

https://www.nibib.nih.gov/science-education/science-topics/magnetic-resonance-imaging-mri

http://www.smithsonianmag.com/smart-news/some-tattoo-inks-can-burn-you-during-mri-180949995/?no-ist

http://www.radiologyinfo.org/en/info.cfm?pg=safety-contrast