Several tests are available to help diagnose colon cancer. While imaging tests, such as MRI, are a beneficial tool, they alone cannot diagnose colon cancer. A doctor typically recommends an MRI after a colon cancer diagnosis. An MRI is useful for determining the location and size of the cancer and whether it has spread to the surrounding organs.

Colon cancer is one of the more common cancers in the United States. The National Cancer Institute predicts that 151,030 people in the United States will receive a new diagnosis of colorectal cancer in 2022. Evidence also indicates that it is the second-leading cause of death due to cancer among Americans.

As such, screening tests, such as stool tests and colonoscopy, are important, as they can help detect cancer before it causes symptoms and when it may be easier to treat successfully. If a doctor suspects colon cancer, they usually conduct further tests, which may involve MRI scans to locate and stage the cancer. This is essential for planning treatment and determining the outlook for those with the condition.

In this article, we will discuss the role of an MRI scan in identifying colon cancer and compare MRI with other imaging and diagnostic tests.

A doctor in surgical clothes looking at vertebral MRI scan.Share on Pinterest
megaflopp/Getty Images

MRI, also known as magnetic resonance imaging, is a useful tool that can help with the diagnosis of colon cancer. MRI scans can play a crucial role in detecting colon cancer and may help guide a doctor in creating a suitable treatment plan. If a doctor suspects colon cancer, they may recommend an MRI scan to help identify the abnormal mass and stage the cancer. An MRI itself does not diagnose colon cancer, but it may help a doctor reach a diagnosis.

An MRI scan uses magnets and radio waves to produce exceptionally detailed cross-sectional images of soft tissues in the body from many angles. Due to these many different views, an MRI scan can identify a tumor’s location and size and tell if it has spread to the surrounding tissues. It can also be a useful tool for monitoring how well treatment is working.

To perform an MRI to detect colon cancer, a medical professional may use a special dye called gadolinium, which creates sharper images and helps the body’s organs show up more clearly on scans. The gadolinium collects around cancer cells, so they appear brighter in the image. This can make it easier for an MRI scan to differentiate between cancerous and noncancerous masses.

A 2019 study comparing the standard imaging pathways, such as CT scan and PET-CT scan, with whole-body MRI found similar accuracy. Using whole-body MRI may reduce staging time, costs, and the number of tests necessary to stage colon cancer.

MRI vs. CT scan

Currently, the CT scan is the standard imaging modality used in preoperative local staging of colon cancer. It has reasonable accuracy in identifying locally and nonlocally advanced colon cancer. However, studies from 2019 and 2017 both suggest that MRI scans may be better at detecting metastasis, or the spread, of colorectal cancer.

MRI scans are slower than CT scans and require the person to remain still. However, CT scans expose a person to more radiation.

Read more about the differences between CT scans and MRI.

MRI vs. ultrasound

Medical professionals typically use ultrasound less often than other imaging modalities, as ultrasound is usually less accurate than the other options. However, ultrasound does have the benefit of being easier and quicker to perform and does not use radiation. Different types of ultrasound a doctor may use for colon cancer include:

MRI vs. X-ray

After a diagnosis of colon cancer, a person may have a chest X-ray to observe whether the cancer has spread to the lungs. However, doctors may use other imaging modalities, as they typically provide better images.

MRI vs. PET scan

A doctor will not often use PET scans for those with colorectal cancer. Instead, they are more likely to use MRI or CT scans. A PET scan involves injecting a radioactive form of sugar that collects mainly in cancer cells.

MRI vs. angiography

Angiography is a form of an X-ray that involves injecting a dye to help emphasize blood vessels in an X-ray. If a person has metastases in the liver, this test can display the arteries that supply blood to those tumors.

MRI vs. barium enema

A barium enema involves using a chalky contrast material to help outline the colon and highlight any abnormalities on an X-ray. However, it is not the most accurate procedure for colon cancer and may only be advisable as an option if other modalities are not possible.

If a person presents with symptoms of colorectal cancer, or if the screening tests show abnormal results, a doctor will recommend several tests to reach a diagnosis. A person will typically undergo these tests before any imaging scans.

Medical and physical exam

Doctors will begin the evaluation by asking about the person’s medical history and family history to learn about their risk of colorectal cancer. They will also ask more questions about the person’s symptoms, such as when they began.

A physical exam may involve palpating any enlarged organs and masses in the abdomen and performing a digital rectal exam. These exams mainly serve to help locate abnormal masses that may require further testing.

Blood in stool

Blood in the stool that is not visible to the naked eye, known as occult blood, can be a sign of cancer. Blood stool tests that can identify the presence of occult blood include guaiac fecal occult blood test (gFOBT) and fecal immunochemical test (FIT). A person can do both tests at home by collecting stool samples in tubes and then sending them to the lab for testing.

Fecal DNA test

Also known as multitargeted stool DNA test (MT-sDNA), or FIT-DNA, this test can detect sections of DNA from cancer or polyp cells. Cells with DNA changes are often present in the stool if a person has colon cancer. This test can also detect occult blood, and a person can perform this test in the privacy of their own home.

Blood tests

Aside from checking for blood in the stool, doctors may recommend blood tests to determine if a person has colon cancer. Doctors also use these tests to monitor the disease and a person’s response to treatment.

  • Complete blood count (CBC): A person with colorectal cancer may have anemia due to long-term bleeding.
  • Liver function test: Liver enzymes may be elevated if the cancer has spread to the liver.
  • Tumor marker cells: Blood tests may also check for a specific protein called carcinoembryonic antigen (CEA).


For this procedure, a doctor inserts a thin, flexible tube with a video camera and light through the anus and into the rectum and colon. They may also use colonoscopy to help them remove polyps and get tissue samples for further testing. Doctors recommend that people who do not have an increased risk of colon cancer undergo colonoscopy every 10 years.

A doctor may also perform a similar procedure known as a sigmoidoscopy. This test uses a shorter tube that checks for polyps or cancer inside the rectum and lower third of the colon. A doctor may perform a flexible sigmoidoscopy every 5–10 years in older adults and people at risk of colon cancer.


While other tests can detect cancer, it is only through a biopsy that a doctor can make a definitive diagnosis of colorectal cancer. A biopsy involves removing a small tissue sample for further examination under a microscope. Doctors typically perform a biopsy during colonoscopy or sigmoidoscopy.

MRI is an imaging scan that a doctor may recommend as an additional test to help diagnose colon cancer. While MRI cannot diagnose colon cancer alone, it plays a vital role in the diagnostic process. Additionally, it helps doctors stage the cancer, which is important for determining a treatment plan and providing an outlook.

Aside from MRI, doctors may also use other imaging modalities, such as CT scan and ultrasound, to help detect colon cancer. By also using diagnostic tests, such as colonoscopy and biopsies, a doctor can accurately diagnose cancer and suggest suitable treatment.