CT scans and MRIs both capture images within your body. CT scans provide pictures of tissues, organs, and skeletal structure, while MRIs are more detailed and can show abnormal tissue.
The biggest difference between MRI and CT scans is that MRIs (magnetic resonance imaging) use radio waves, and CT (computed tomography) scans use X-rays.
Which one a doctor orders can depend on why you are having the scan performed and what part of the body the doctor would like to be imaged. They vary by what they can capture, which may make one a better option depending on your circumstances. Some of the differences between them include:
| CT scans | MRI scans |
|---|---|
| faster (typically 5 to 10 minutes) | longer (typically 20 to 90 minutes) |
| uses X-ray technology to produce images | uses magnetic field to produce images |
| produces detailed images of bones and less detailed images of soft tissue | produces highly detailed images of soft tissue |
| less expensive | more expensive |
Keep reading to learn about the different situations in which MRIs and CTs are recommended and the possible risks and benefits.
MRIs produce three-dimensional images of structures inside the body using radio waves and magnets.
A constant magnetic field and radio frequencies bounce off the fat and water molecules in your body. Radio waves are transmitted to a receiver in the machine, which translates them into an image of the body.
Because an MRI uses strong magnets, extra precautions are required to ensure you don’t have anything magnetic in or on your body.
They can help doctors visualize non-bony body parts, including soft tissue like muscles. They’re frequently used to diagnose issues with your:
Doctors may use an MRI instead of a CT scan if, for instance, you are pregnant but require imaging. However, they typically use them with caution and only when necessary.
Doctors may also use MRI to monitor certain health conditions, including:
- multiple sclerosis
- herniated discs
- brain or spine tumors
- epilepsy
- meningitis
Is a magnetic resonance angiography (MRA) an MRI?
An MRA is a type of MRI used to visualize:
- heart
- blood vessels
- arteries
Doctors may use it instead of a traditional angiogram, as it is less invasive.
If you’re getting an MRI, let your technician know if you have any implants in your body, such as pacemakers or stimulators. An MRI uses strong magnets, and not all metals are compatible.
A technician may ask you to change into provided clothing before the test.
An MRI usually takes between 20 and 40 minutes, but can take up to 90 minutes, depending on the parts of the body that require imaging and whether or not you need to re-take any images.
An MRI requires that you lie very still for specific intervals. If you move while the machine is capturing images, you may have to repeat those images.
A technician may let you know how many minutes each portion of the MRI will take and when you might be able to move or shift. They may also ask you to reposition or hold your breath briefly.
An MRI makes loud thumping noises during the scan. Typically, you’ll be offered earplugs or headphones to make the noise more bearable. Your technician may also play music of your choice during your MRI.
Depending on why you’re getting an MRI, a doctor may order one with contrast. Contrast is a fluid usually administered intravenously (through an IV). These gadolinium-based contrast agents make certain features easier to see on MRI images. CT scans with contrast use a different contrast agent. Note that using contrast may not be safe for people with kidney disease.
If you have anxiety or claustrophobia
MRI machines are open on both ends. This can help with claustrophobia (a fear of small spaces) or anxiety. However, some people experience anxiety or claustrophobia when getting an MRI. If you are concerned about this, it may help to:
- talk with your doctor
- wear an eye mask
- use a blanket
- close your eyes
Doctors may also recommend MRIs under sedation, especially for children.
A CT scan is a form of X-ray that involves a large X-ray machine. CT scans are sometimes called CAT scans.
They take detailed cross-sectional X-ray images that are quicker, but less detailed than MRIs in showing soft tissue.
A CT scan is typically used for:
- emergencies, like finding internal bleeding, bone fractures, bowel blockages, or blood clots
- locating tumors in certain organs
- monitoring possible cancer spread to other areas of the body
During a CT scan, you’ll lie down on a table.
The table then moves through the CT machine, which can look like a large ring, to take cross-sectional pictures inside your body.
The machine is not as loud as the MRI machine. It also takes only a few minutes.
Doctors may also order CT scans with an iodine-based contrast. This contrast is different than the type used for MRI scans and is not safe for use in people with an iodine allergy.
CT scans are more widely used than MRIs and are typically less expensive. They’re often used for emergencies.
You may get a CT scan if doctors aren’t sure of the cause of your symptoms. Sometimes, after reviewing your CT results, a doctor may order an MRI to view a part of the body in greater detail.
MRIs, however, are considered superior in terms of image detail. The most notable difference is that CT scans use X-rays, while MRIs do not.
Other differences between MRI and CT scans include their risks and benefits:
Risks
Both CT scans and MRIs pose some potential risks, which depend on the type of imaging and how it is performed.
CT scan risks include:
- harm to unborn babies
- variable dose of ionizing radiation based on the specific scan performer and how often scans are performed
- a potential reaction to the use of dyes
MRI risks include:
- reactions to implanted metals due to a strong magnetic field
- loud noises from the machine over time may cause hearing issues
- increase in body temperature during long MRIs
- claustrophobia and anxiety
- complications from the use of dyes in people with kidney disease
You should consult a doctor before an MRI if you have any implants, including:
- artificial joints
- eye implants
- an IUD
- a pacemaker
Benefits
Both MRIs and CT scans can view internal body structures. However, a CT scan is faster and can provide pictures of tissues, organs, and skeletal structure.
An MRI is highly adept at capturing images that help doctors determine if there are abnormal tissues within the body. MRIs are more detailed in their images.
Your doctor will most likely recommend whether you should get an MRI or a CT scan based on your symptoms.
If you need a more detailed image of your soft tissue, ligaments, or organs, your doctor will commonly suggest an MRI.
Such cases include:
- herniated disks
- torn ligaments
- soft tissue issues
If you need a general image of an area like your internal organs, or due to a fracture or head trauma, a CT scan will commonly be recommended.
Both CT scans and MRI scans are relatively low risk. Both offer important information to help your doctor properly diagnose specific conditions.
Your doctor will most likely tell you what they recommend. Be sure to ask questions and discuss any concerns with your doctor so you can be comfortable with their recommendations.