Imaging Tests for Cancer: Scans Explained

Imaging tests create pictures of areas inside your body. These pictures help your doctor see whether a tumor is present, where it is, and sometimes whether it has spread. There are several ways to make these pictures, and each works a little differently.

No single imaging test can diagnose cancer by itself. Scans are used together with lab tests and, in most cases, a biopsy.

A CT scan uses an X-ray machine linked to a computer. It takes a series of pictures of your organs from different angles. The computer combines them into detailed 3-D images. You lie still on a table that slides into a donut-shaped scanner, and the machine moves around you taking pictures. Sometimes you receive a contrast material (dye), swallowed or by vein, first to make the pictures easier to read.

An MRI uses a powerful magnet and radio waves, not radiation, to take pictures of your body in slices. The slices are combined into detailed images that can show places where there may be tumors. During an MRI you lie still on a table that is pushed into a long chamber. The machine makes loud thumping noises and rhythmic beats. Sometimes a special contrast dye is injected into a vein to make tumors show up more brightly.

If your MRI report uses words like enhancing lesion or contrast enhancement, those words describe how an area appears after contrast. They are clues for interpretation, not diagnoses by themselves.

A nuclear scan uses a small amount of radioactive material to make pictures of the inside of the body. Before the scan, you receive an injection of a tracer that flows through your bloodstream and collects in certain bones or organs. A scanner then detects the radioactivity and creates pictures.

A bone scan is a type of nuclear scan that checks for abnormal areas or damage in the bones. It may be used to help diagnose bone cancer or to find out whether cancer has spread to the bones from elsewhere in the body. Areas where the material collects are sometimes called "hot spots."

Bone-related reports may also use phrases like bone lesion, lytic lesion, or bone metastasis. The wording matters, but the next step depends on the scan pattern and your clinical context.

A PET scan is a type of nuclear scan that makes detailed 3-D pictures of areas inside your body where glucose (a sugar) is taken up. Because cancer cells often take up more glucose than healthy cells, these areas can show up on the scan. Before the scan you receive an injection of a tracer, and during the scan you lie on a table that moves through the scanner. PET is often combined with CT in a single PET/CT procedure.

An ultrasound exam uses high-energy sound waves that people cannot hear. The sound waves echo off tissues inside your body, and a computer uses those echoes to create a picture called a sonogram. During the exam, a technologist moves a device called a transducer, covered with a warm gel, over the skin of the area being examined. Ultrasound does not use radiation.

X-rays use low doses of radiation to create pictures of the inside of your body. A technologist positions you and directs the X-ray beam to the correct area. While the image is taken, you need to stay very still and may be asked to hold your breath for a second or two.

Results from imaging are posted in your patient portal and read alongside your other tests. It is normal to want to know right away what a scan shows. But your doctor is the best person to explain what the results mean for you — and to decide whether more tests, such as a biopsy, are needed.

For lymph node wording, start with enlarged lymph node, reactive lymph node, and subcentimeter lymph node.

If the scan report names a finding and you need the next-step version, these guides may help: lung nodule on CT, liver lesion on CT, enlarged lymph node on a scan, incidental pancreatic cyst, thyroid nodule on ultrasound, ascites, omental caking, mediastinal lymph nodes, peritoneal nodules, adnexal masses, and complex cysts.

If your scan uses a reporting system, start with TI-RADS, TI-RADS 4, BI-RADS 3, BI-RADS 4, BI-RADS 5, PI-RADS 3, PI-RADS 4, PI-RADS 5, and LI-RADS 3/4/5.

Contrast material (dye) is the part of imaging most likely to cause a reaction. It is contrast material (dye), given for some CT and MRI studies.

• Call 911 or go to an emergency department if in the minutes or hours after a contrast injection you struggle to breathe, your face, lips or tongue swell, hives spread over your body, or you feel faint. A severe contrast reaction, called anaphylaxis, is rare but life-threatening. If this starts while you are still in the scanner, tell the operator straight away — they can hear you.
• Call your care team the same day if itching, hives, sneezing, nausea or vomiting begin after a scan done with dye, or if you are passing noticeably less urine than usual in the day that follows. Contrast can affect how the kidneys work, especially in people with kidney disease or diabetes. Tell staff about kidney disease, diabetes, or metformin before your scan.

Sources: MedlinePlus — CT scan; NCI — Cancer Diagnosis.