What's the Difference Between a CT Scan and MRI?

CT scans and MRIs are two of the most common types of medical imaging. The healthcare industry has used both medical imaging tools for decades to diagnose all types of health conditions. CT scans and MRIs use different methods but achieve the same goal: They allow medical professionals a glimpse into what’s happening inside their patients' bodies.

CT Scans and MRIs: What are They?

A CT scan uses ionizing radiation to produce images of cross-sections (slices) of your body. An MRI uses magnetic fields and radio waves to see parts of your organs. While both scans can show doctors details about your organs, bones, and other tissues, each scan has unique benefits. Let's take a closer look at how both of these differ.

The Difference Between a CT Scan and MRI: A Quick Overview

The main difference between CT scans and MRIs is how they create pictures. CT scans use x-rays, while MRIs use magnets and radio waves.

CT scans are also quicker than MRIs. They can sometimes provide more detailed images of larger areas, while MRIs can provide more detailed images of smaller or more diffuse regions.

MRIs are better at showing soft tissues, such as the spinal cord and ligaments, than CT scans. They're also better at detecting certain types of tumors, bleeding in the brain, and problems with the spinal cord and joints.

Both CT scans and MRIs are painless procedures.

What are CT Scans Used For?

A computed tomography (CT), sometimes referred to as computerized axial tomography (CAT), is a form of imaging that makes use of specific x-ray equipment to produce detailed scans of regions inside the body. CT scans show more detail than regular x-rays, so they are used to diagnose a variety of health conditions, including:

• Tumors.
• Bone fractures.
• Internal bleeding.
• Infections.

Your doctor may recommend a CT scan if you have symptoms such as:

• Severe stomach aches or abdominal pain.
• Chest pain.
• An injury.

You may also have a CT scan to check for problems after an accident or surgery. If you've had a head injury, your doctor may use a CT scan to check for bleeding or skull fractures.

What to Expect During a CT Scan

During a CT scan, you’ll have to lie on your back on a motorized table that slides into the CT scanner. An x-ray tube will rotate around your body and take pictures of cross-sections, or slices, of your body.

An x-ray technologist will be able to see you at all times and will give you instructions. They may tell you to hold your breath for short periods during the scan. This helps prevent blurring in the images.

In some cases, you may receive contrast dye before the CT scan. Contrast dye is a liquid that helps highlight specific areas in your body. It can also help show problems with the blood vessels in your body, such as blockages or aneurysms.

After the CT scanner takes a series of x-rays of your body, the table then slides out of the CT scanner. The pictures are sent to a computer, where a radiologist will review them and send a report to your doctor. The whole process usually takes about 30 minutes or less.

What are MRIs Used For?

Magnetic resonance imaging (MRI) takes pictures of the organs in the body using strong magnetic fields and radio waves.

MRIs are used to diagnose problems involving body parts like the:

• Brain.
• Spine.
• Nerves.
• Joints.

You may be prescribed an MRI if you have:

• Signs of a stroke, such as weakness or numbness in your arm or leg.
• Symptoms of a brain tumor.
• Injuries to your ligaments or tendons.

An MRI can also be used to check for problems after surgery. If you've had surgery to remove a brain tumor, an MRI can help show whether any cancer cells are still present.

What to Expect During an MRI 

An MRI machine is a large cylinder, called a “bore,” that contains a powerful magnet. You will be asked to lie on a table that slides into the cylinder. During the MRI, you will hear loud thumping and humming noises. A technologist will give you headphones and offer music of your choice, to help block out the noise. Via these headphones, the patient will also have constant communication with the technologist. You may also be given a contrast dye through an IV line before your MRI, like a CT scan.

After the MRI machine is finished taking images of your body, the table then slides out of the tube. The whole process will usually take 30 to 60 minutes.

Are CT Scans and MRIs Safe?

CT scans and MRIs are generally considered safe for most people. There’s a very low risk of experiencing side effects due to the x-rays or magnetic fields used during these procedures. However, there is a number of factors that can influence this risk:

• For one, the contrast dye used during a CT scan or MRI can cause allergic reactions in some people. In rare cases, the contrast dye can also cause kidney problems.

• There’s also a small risk of CT scans and MRIs harming pregnant individuals. Let your doctor know if you're pregnant so that they can reevaluate the next steps.

• If you have metal implants in your body, such as a pacemaker or artificial joints, be sure to inform the technologist before either procedure. Metal can cause problems with the images produced during a CT scan or an MRI. 

• The enclosed space of the MRI tube can also be anxiety-inducing for some people. If you have claustrophobia, you may want to ask your doctor if an "open wide bore" MRI is available. Wide bore MRIs are larger and may be less likely to cause anxiety.

The Bottom Line

Both CT scans and MRIs are essential tools doctors use to diagnose many different conditions. These procedures are generally considered safe for most people. Your doctor will usually recommend a CT scan or MRI based on the type of problem you're having.

Be sure to ask your doctor about the risks and benefits of CT scans and MRIs before having either procedure. They can help you decide what the appropriate course of action is for you. And if you’re ready to take the next step with SDMI, learn more about what to expect from your visit.