MRI Imaging

Magnetic Resonance Imaging (MRI) is a non-invasive scanning method that produces detailed pictures of organs, bones, muscles, and blood vessels. Instead of ionizing radiation, it relies on a strong magnetic field paired with radio waves, which makes it a common alternative to CT scans when doctors need a closer look at soft tissue.

How it works

The scanner surrounds the body with a powerful magnetic field that briefly lines up the atoms in your tissue. Pulses of radio waves knock those atoms out of alignment, and as the pulses stop, the atoms settle back into place and give off a faint signal. A computer picks up that signal and reconstructs it into a cross-sectional image on a monitor.

Open vs. closed scanners

Traditional closed MRI machines fully enclose the patient in a tube. They generally produce sharper images and finish faster, since their stronger magnets pick up more detail. The trade-off is comfort: the enclosed space can be difficult for people with claustrophobia or for larger patients.

Open MRI machines leave the sides uncovered, using magnets positioned above and below the patient instead of around them. This layout is easier on anxious or larger patients, but the weaker magnetic field usually means longer scan times and somewhat lower image resolution.

Other uses

• MRA (Magnetic Resonance Angiography): checks blood flow through arteries and can help spot aneurysms or vascular abnormalities.
• fMRI (Functional MRI): maps brain activity by having the patient perform a task, helping doctors locate the areas responsible for functions like speech or memory before surgery.

Getting ready for a scan

• Most patients can eat, drink, and take regular medication beforehand, though some specialty exams have their own restrictions.
• You'll be asked to remove clothing, jewelry, and anything metallic, and change into a gown.
• The scan takes place inside a tube-shaped machine open at both ends. Staying completely still is important for clear images, and earplugs are provided for the loud noise.
• If contrast dye is required and you've reacted to it before, let your doctor know in advance so you can be prescribed the right premedication.
• Anyone with anxiety about enclosed spaces can ask a doctor about anti-anxiety medication ahead of time — arrange for a ride home if you take it.

Important to disclose beforehand

Tell your doctor in advance if any of the following apply:

• A pacemaker or replaced heart valve
• An implanted pump, such as an insulin pump
• Vessel coils, filters, stents, or clips
• Pregnancy or possible pregnancy
• A past bullet wound
• A history of working with metal (e.g. grinding or welding)
• Metal fragments anywhere in the body
• Difficulty lying still for 30–60 minutes

During the scan (roughly 15–90 minutes)

You'll lie on a table that slides into the scanner, sometimes with padding or straps to help you stay still. A technologist watches and communicates with you throughout from an adjoining room, and you'll be given a way to signal them if needed. You may be asked to hold your breath briefly at certain points. If contrast dye is used, some people notice a brief coldness, a metallic taste, mild nausea, or a short headache as it's injected. The scan itself isn't painful, though lying still for an extended period can be uncomfortable, especially after a recent injury or surgery.

After the scan

Stand up slowly to avoid lightheadedness. If you received a sedative, plan to rest until it wears off and arrange another way home. Watch the IV site for redness or swelling, and contact your doctor promptly if you notice any signs of a reaction to contrast dye, such as itching, rash, or trouble breathing — treat difficulty breathing as an emergency. Otherwise, most people can return to their normal routine right away.

Why MRI machines are expensive to maintain