Understanding brain tumor imaging: CT scan vs. MRI

Brain tumors are abnormal growths of cells in the brain that may or may not be cancerous. To diagnose a brain tumor or to check on its growth, your doctor will use special imaging to view the brain. There are two types of imaging typically used to view brain tumors: a computed tomography (CT) scan and magnetic resonance imaging (MRI). Both imaging techniques have unique and important roles to play in detecting and monitoring brain tumors.

Understanding CT scans

CT scans create detailed images of the inside of your body. In addition to your brain, CT scans can also create clear pictures of your bones, muscles, tissue, organs and blood vessels. These images help doctors view and accurately diagnose conditions like brain tumors, blood clots and internal bleeding.

A CT scan is basically a series of x-rays piled together to create a 3D image. These are often used to screen for disease because they do not take much time to complete, and they clearly show boundaries between different parts of the body.

“CT scans are good for getting a thousand-foot view of the brain. You can see something abnormal in the brain, such as bleeding, a large tumor or irritation in the brain,” said Dr. Angela Richardson, an IU Health neurosurgeon. “CT scans are typically the first imaging you will get in an emergency room because it shows things that are more urgent and can be treated right away.”

During a CT scan, you will be asked to lay on a table as the donut-shaped CT machine rotates quickly around your body. During this time, the CT machine is using radiation to gather image data from multiple x-ray beams. The process is completely painless and only takes a few minutes.

CT scans, like x-rays, deliver a small amount of radiation. However, you should never receive more radiation than necessary. A computer turns these images into a detailed picture that is read by a board-certified radiologist.

Understanding MRIs

An MRI is essentially a large magnet that uses radio waves to pick up signals on what’s happening inside the brain. During an MRI, you will lie down on a table that moves through a larger, tube-shaped scanner. The magnets in an MRI spin around your body and then assemble the radio waves into detailed images of structures inside the brain.

MRI machines take longer to capture than CT scans, usually lasting up to 45 minutes. During this time, you will need to lie completely still for the scan. You may be able to listen to music during an MRI.

Unlike CT scans or x-rays, MRIs do not give off ionizing radiation and are perfectly safe for use and re-use.

“As far as you know, we can take repeated MRIs on a patient. They’re so safe that we offer them to pregnant patients,” said Dr. Matthew Pease, IU Health neurosurgeon.

MRI vs. CT scan

The advantage of an MRI scan over a CT scan is that the images are very high resolution and can more easily show different structures like a brain tumor.

“I like to compare CT scans to those old, black-and-white televisions from the 60s that our parents or grandparents used to watch,” said Dr. Pease. “Now, compare that to an MRI, which–in this scenario–is more like a fancy, high-definition, 4K television. The quality is better in an MRI, but the CT scans are used all the time because they’re quicker to take and the images come back sooner. With an MRI, you have to wait a day or two for results.”

“New MRIs also have a camera with a really good zoom that lets us see much smaller things in much greater detail, so we can gather a lot more information,” Dr. Richardson said.

Both machines may use something called “contrast dye” to make certain structures inside the body more visible. If your doctor orders contrast, a harmless liquid will be injected into your body before or during your scan to make the images clearer.

You can wear jewelry or metal in a CT machine, but it’s very dangerous to have metal near an MRI because of its strong magnet. If you have a metallic implant or pacemaker in your body, your doctor will need to check to make sure the implant or device is safe for MRIs.

Imaging to fit your needs

The decision about which imaging option to use to view the brain depends on several factors, including urgency, imaging goals and your body. Be sure to ask your doctor any questions you may have about the type of imaging recommended for you and what you can expect from the scan. Both CT and MRI imaging offer important tools for doctors to view the brain, and your care may involve both techniques.