CT Scan vs. MRI: What’s the Difference?

Getting the right diagnosis often starts with the right imaging test, but how do you know which one is right for you? If your doctor has recommended a CT scan or an MRI, you might be wondering what the difference is — and why one might be chosen over the other. Both tests provide important information about your health, but they work in different ways and offer unique advantages.

To help you better understand how each test works and when it might be used, we asked three of our expert radiologists — Oguz Akin, MD (Service Chief in Body Imaging), Richard Do, MD, PhD (Director of MRI), and Andrew Plodkowski, MD (Director of CT).

What is the difference between a CT scan and an MRI?

What is a CT scan, and what does it show?

CT stands for computed tomography. A CT scan uses X-rays to create detailed cross-sectional images of the body. During the procedure, you’ll lie on a table that moves through a scanning ring that is shaped somewhat like a large doughnut. The CT scan itself takes only a few minutes. Once the images are taken, they’re processed into clear, layered pictures that help doctors see your organs, bones, and tissues with precision.

What is an MRI, and what does it show?

MRI stands for magnetic resonance imaging. Like a CT scan, an MRI creates highly detailed images of your body’s internal structures — but it does so with strong magnets and radio waves instead of X-rays. You will lie on a table that slides into the cylindrical scanner. The procedure typically lasts between 20 and 40 minutes. The scanner makes loud tapping or thumping sounds during the imaging process.

What are the advantages of CT scans, and when do doctors choose them?

CT scans are fast and often used when doctors need to make quick decisions, such as in emergency situations. Their speed and accuracy make them an ideal first test for evaluating a wide range of conditions. CT scans are often used in cancer care to assess whether cancer has spread to the lungs, liver, other organs, or bones. They’re also commonly used to detect other conditions such as infections, internal bleeding, blood clots, bowel blockage, and so on. Because CT scans offer a comprehensive view of the body in just seconds, they’re an essential tool for prompt diagnosis and treatment planning.

What are the advantages of MRIs, and when do doctors choose them?

MRI offers even greater detail when a more focused view is needed, especially for certain organs and soft tissues. It can detect certain cancers — such as those of the prostate, breast, or liver — that may be harder to see on CT. MRI is also the preferred method for evaluating cancer that may have spread to the brain or bone because it can detect subtle changes. One major benefit of MRI is that it does not expose patients to ionizing radiation, making it a safer option for people who need repeated scans or who are particularly sensitive to radiation, such as children or pregnant women.

What concerns do people have about CT scans and MRIs?

Both CT and MRI are safe, noninvasive, and generally well tolerated. CT scans do involve a small dose of ionizing radiation, but this is carefully controlled and minimized. The benefits of accurate diagnosis usually far outweigh this minor risk. It’s important to remember that your doctor has recommended a CT scan because it offers valuable information needed for your care — and when used appropriately, it’s a very safe and effective tool. The scans are quick, and in many cases, a contrast dye is used to enhance the clarity of the images. Most people tolerate this contrast well. CT is also accessible to nearly everyone, even those with medical implants, which may not be the case with MRI.

MRI does not use radiation, but the procedure takes longer and requires you to stay still in a more enclosed space, which can be difficult for people with claustrophobia. The machine makes loud noises while scanning, but ear protection is provided to make you more comfortable. Some implants, such as pacemakers or stimulators, may limit your ability to have an MRI, though many newer devices are MRI-compatible. Like CT, MRI may involve the use of contrast material, depending on what needs to be examined.

How AI is improving MRI and CT scan imaging — and your care

Artificial intelligence (AI) is becoming a tool in radiology, not to replace radiologists performing MRIs and CT scans, but to make them even more precise. At MSK, we’re exploring how AI can help identify patterns in scans that might be otherwise hard to detect, suggesting areas for closer review. AI can also enhance image quality, making it easier for radiologists to assess changes in tumors over time — such as shrinkage or growth.

While AI adds an extra layer of analysis, your scan will always be reviewed by a highly trained radiologist who brings years of expertise to the final interpretation. AI simply helps us focus faster on what matters most.

How we choose the right scan for you

At MSK, our radiologists personalize every imaging decision based on your condition, symptoms, and medical history. In many cases, a CT scan is the first step, especially when we need a quick and broad view of the body. If more detail is needed or if your condition requires it, we may recommend an MRI. Sometimes, a CT scan reveals something that prompts a follow-up MRI for closer examination.

If you have concerns about either type of imaging — whether it’s claustrophobia with MRI or worries about radiation from CT — our team will work with you to find the safest, most comfortable solution. The goal is always to provide the clearest possible picture to guide treatment while respecting your individual needs.

For more information, see our patient information pages:

What to expect at your appointment for a CT scan.

What to expect at your appointment for an MRI.

Also, learn about the expertise of MSK’s Department of Radiology.