Key takeaways:
CT scans and MRIs are two types of radiology tests used to take a closer look inside the body.
These tests use very different types of technology, so they each have their own unique advantages and disadvantages. One might be better than the other depending on the situation.
Imaging tests can be very helpful but are not always necessary to reach a diagnosis.
Sometimes, you have a symptom or condition that cannot be seen on the surface. When you sense that something in your body is feeling different, there are many ways to take a closer look. Computed tomography (CT) scans and magnetic resonance imaging (MRIs) are both helpful tests to see inside our bodies. But it can be hard to know which test is best for you.
CT scans and MRIs use different types of energy waves to create a picture of the inside of our bodies. CT scans use radiation waves (like an X-ray), and MRIs use magnetic waves. This means one is usually better than the other depending on the symptoms or suspected diagnosis. We’ll explain in more detail how these tests work and the advantages specific to each one.
What is a CT scan?
A CT scan is a special type of X-ray that takes thousands of tiny pictures of the body from all different angles. A computer can then reconstruct these images into a three-dimensional (3D) image of any part of the body. CT scans give detailed information about dense structures in the body, such as bone, or solid organs like the liver or spleen. It is less effective for softer or hollow parts of the body like muscle or intestine.
Search and compare options
To get more detail, sometimes an iodine-based contrast is given by mouth or an IV. This lights up certain parts of the image so that it is easier to see. When the contrast is given through an IV, it lights up the blood vessels. When given by mouth, it lights up the stomach and intestines. These are just two examples of the many ways that contrast can provide more detailed images.
A CT scan machine has the appearance of a donut. The patient lies on a table that moves through the center of the donut while pictures are taken.
A CT scan has several advantages:
Provides detailed images of bones and solid organs like the liver, spleen, or brain.
Detects things like tumors, abnormal bleeding, inflammation, and infection in most organs.
Less expensive than an MRI.
Quicker than MRI — making them particularly helpful in emergency situations.
More tolerable for people who get claustrophobic, or people who cannot sit still for long periods of time.
A CT scan also has some disadvantages:
Uses radiation waves — meaning that frequent CT scans can expose you to high levels of radiation over time. This puts some stress on the body’s cells and can increase the risk that a cell will become cancerous.
Sometimes provides less-detailed images than an MRI.
Some people cannot safely receive the contrast. This includes people who are allergic to it and those who have kidney disease. Adequate kidney function is needed to get the contrast out of the body, or the contrast can damage the kidneys.
Comparing imaging tests: CT scans and X-rays are both used to take a closer look inside the body. Learn more about the differences between the tests, including the pros and cons of each.
Paying for an MRI: Most insurance plans cover MRIs, though you might have some out-of-pocket costs. Here’s what you can expect to pay, and what factors might affect the price.
Getting answers: Imaging tests can help identify causes for many different symptoms, including back pain. Three people share their experiences with a slipped disc and how they were diagnosed.
What is an MRI?
An MRI is one of the most detailed imaging tests available. The machine uses magnets to produce energy waves that pass through the body. They produce detailed images that are then reconstructed into a 3D picture.
Read more like this
Explore these related articles, suggested for readers like you.
An MRI can show delicate tissues such as muscle, blood vessels, and nerves. Like CT scans, MRIs with contrast can create even greater detail. The name of the contrast is gadolinium, and it can be given by mouth or through an IV.
An MRI machine looks like a long tube. And some are more open than others. The patient lies on a table inside the tube as the magnets do their work.
MRIs have some specific advantages:
Provides detailed images of certain parts of the body. Some examples include muscle, tendon, cartilage, nerves, and blood vessels.
Detects tiny abnormalities that can be missed on a CT scan. Some examples include small strokes in the brain, early signs of infection in an organ, nerve inflammation, or narrowed blood vessels.
Lower radiation exposure. This can make the test better for people who should limit radiation exposure, like pregnant mothers, or cancer patients who receive multiple imaging tests.
Gadolinium contrast is less likely to cause allergic reactions or kidney injury.
MRI also has some drawbacks:
They are much more costly than CT scans and other imaging tests. This is due to the more expensive costs of equipment. It also takes more time for radiologists to read these detailed images.
MRI tests can be difficult for people who are claustrophobic. There are “open” MRI machines that can help, but these machines can sometimes compromise image quality.
MRI tests can take a long time — sometimes an hour or longer. This can be difficult for someone who cannot lay still on a table.
They make a loud humming noise when operating. Patients are often provided with earplugs for comfort.
How do I know which test is best for me?
If you think you might need an imaging test, start with a discussion with your medical provider. This information should give you a good starting point to begin these discussions. Healthcare providers are trained on when to order the right test, at the right time, for the right problem.
And if you are interested in learning a little bit more, the American College of Radiology (ACR) has also developed criteria to help select the best imaging test. This resource is available online and can be used by both providers and patients. It gives helpful guidance to choose the best test based on your symptoms or possible diagnosis.
And, sometimes, no imaging is needed at all. A good example of this is a migraine. Even though the problem is going on inside the brain, a CT or MRI of the head would likely be normal. The diagnosis is made based on someone’s symptoms. In fact, the American Board of Internal Medicine (ABIM) has launched a campaign to cut back on unnecessary imaging tests.
The bottom line
CT scans and MRIs are both valuable tools in diagnosing many different types of medical conditions. And, depending on the situation, one may be better than the other. CT scans can provide quick, detailed images of most of our internal organs. MRIs can sometimes provide even more detail, but they can take a lot longer — and be more uncomfortable. If you are considering an imaging test, talk to your provider about which test is best for you and your situation.
Why trust our experts?
References
American College of Radiology. (2021). Appropriateness Criteria List.
Center for Medicare & Medicaid Services. (2021). Procedure Price Lookup for Outpatient Procedures.
Choosing Wisely: An Initiative of the ABIM Foundation. (2021). Patient Resources.
National Institute of Biomedical Imaging and Bioengineering. (2021). Computed Tomography (CT).
National Institute of Biomedical Imaging and Bioengineering. (2021). Magnetic Resonance Imaging (MRI).
