CAT Scan

CAT Scan

Reviewed By:
Martin E. Liebling, M.D., FACP


A CAT (computed axial tomography) scan, or CT scan, is a painless test that uses special x-ray equipment to obtain multiple images of internal body structures. The images are then placed together by computer technology to produce cross-sectional views of the targeted area. CAT scans use digital x-rays which provide greater detail than standard x-rays.

CAT scans are usually performed in a hospital, outpatient clinic or imaging center. They are typically performed by a radiologist and radiology technicians who specialize in these types of imaging exams. The results of a CAT scan may be interpreted by a variety of physicians (e.g. oncologist, surgeon), depending the purpose of the test.

CAT scans are taken in a special device that contains a donut-shaped tube with a movable bed in the center. The tube contains both an x-ray source and rows of x-ray detectors. The x-ray source is rotated 360 degrees around the patient, who is placed on a table within the tube. As the table moves through the tube, multiple images are taken from various angles. The screen and computer that analyzes the images are usually located in a separate area or room.

In some cases, a special dye (contrast medium) may be given to the patient (e.g., swallowed, intravenously or by enema) and a second set of pictures is taken. The dye helps highlight certain regions of the body to provide a clearer view.

The time required for a CAT scan depends upon the area under study and the type of CAT scanner being used for the procedure. Generally, a CAT scan takes 10 to 20 minutes, but may take up to an hour to complete. Some patients may be given a sedative for the procedure and they will not be able to drive themselves home from the test site. Otherwise, patients can return to their usual daily activities.

CAT scans are frequently used to diagnose a number of medical conditions, including cancer. The test can help detect malignant tumors and provide information about their size and location. In addition, CAT scans can be used to help guide biopsies inside the body, and to help plan radiation therapy or surgery.

About CAT scans & cancer

A CAT (computed axial tomography) scan, or CT scan, is a painless diagnostic test that uses x-ray equipment to create multi-dimensional images of body structures. These images, which are taken from different angles around the body, are placed together by a computer to form cross-sectional views of the targeted area. Increasingly, CAT scans use digital x-rays to produce more detailed images on a computer screen.

Similar to standard x-rays, CAT scans use radiation to obtain the pictures. However, x-rays use a single dose of radiation while CAT scans use numerous x-ray beams and detectors that rotate around the body. CAT scans use slightly more radiation than x-rays but the valuable information obtained from the test generally outweighs the risk.

CAT scans may be used to diagnose or help treat cancer in the following ways:

  • Detect or confirm the presence of tumors

  • Guide a biopsy (removal of cells or tissues for analysis) inside the body

  • Help plan surgery and/or radiation therapy

  • Assess the cancer’s response to treatment

Body regions that can be examined with a CAT scan include:

  • The chest (thoracic CAT scan). Can produce very clear pictures of the heart and lungs. Cancerous tumors of the lungs and swollen lymph nodes are among the conditions that can be detected by CAT scans. These scans may be particularly helpful in determining the spread or stage of cancer.

    CAT scans generally are not used to screen for breast cancer because the amount of radiation needed to detect a small lump is too high to be considered safe.  

  • The head. To determine the course of emergency treatment for a stroke. The head CAT scan may allow physicians to determine whether a stroke is due to a cerebral hemorrhage or blood clot. It may also help the physician locate the exact position of the damage. In addition, CAT scans can detect the presence of primary brain tumors or metastasis and can also detect intracranial bleeding. 

  • The back. To assess for any bulging discs, spinal cord tumors or structural abnormalities.

  • The abdomen. To assess for any structural abnormalities of the liver, kidneys, pancreas or other internal organs.

A number of people in the United States choose to have preventive CAT scans performed on an annual basis. These full-body CAT scans are done to detect certain diseases in their very early stages but their value is highly controversial among medical experts.

Critics point out that the scans can image benign conditions that may require a series of follow-up tests that only incur an increase in time and expense. Another concern is that individuals may think that a preventive CAT scan is a suitable alternative to regular physical examinations with their primary care physician or to other valuable diagnostic tests, such as a colonoscopy. Also, patients may erroneously believe that a negative scan rules out the presence of a disease process.

It has been suggested that preventive CAT scans be reserved for higher risk individuals, rather than healthy, asymptomatic people younger than 40 years of age who do not have a family history of heart disease, cancer or other diseases.

Numerous studies have examined the use of CAT scans as a screening tool for lung cancer in high-risk patients. Results of the studies have created a controversy among healthcare professionals. Although the results suggest that certain types of CAT scans may detect small lung cancers, the scans have not appeared to improve the survival rates. In addition, the scans may increase the number of unnecessary, risky surgical procedures (e.g., lung biopsies). Additional studies are needed to further evaluate the value of CAT scans for lung cancer.

Because a CAT scan involves the use of radiation, CAT scans are not generally recommended for pregnant women, due to risk to the fetus. All individuals should report any history of blood-clotting disorders, kidney disease or allergic reactions to iodine, shellfish or strawberries prior to undergoing a CAT scan. These elements may create complications in a patient if a physician intends to use a contrast medium (dye) in the scan.

Before, during and after the CAT scan test

No special preparation is required for a CAT scan, unless the physician wishes to use a special dye (contrast medium) and/or a sedative before the test. If a contrast medium will be used, then patients are generally asked not to eat or drink for about four to six hours before the test.

Immediately before the test, patients typically change into a hospital gown and must remove any metal objects (e.g., jewelry, eyeglasses, dental appliances). Patients are asked to lie down on a scanning table, which slides slowly into a short, open-ended tunnel. Pillows or straps may be used to help keep the patient in the correct position. The technician will conduct the test from a separate area but will be able to view the patient and scanner.

The first set of images may be taken without any contrast medium. If requested by the physician, a second set may be taken with the use of dye. The dye may be injected through an intravenous (IV) line, producing a warm, flushed feeling. This may last for several minutes and is normal.

In some instances, patients may be asked to drink a liquid containing contrast material or may receive the material through an enema. The type of dye used will vary according to the purpose of the scan.

After the scan begins, patients will be instructed to lie very still, and may be asked to hold their breath for short periods of time. The scanner may make whirring, buzzing or clicking sounds during the procedure. However, there are speakers and a microphone in the machine to allow patients to communicate with the technician who is conducting the test. Many facilities offer music to help mask the sound of the scanner and help patients relax.

In a conventional CAT scan, the “x-ray sensing unit” and detectors rotates around the body part that is being scanned, while the table moves by a fraction of an inch between scans. Patients are urged to speak with the technician if they are feeling uncomfortable or concerned about the sounds made by the machine or any other aspect of the test. Depending on the kind of CAT scan, it takes from 10 minutes to an hour to complete the test.

The patient typically remains on the table until the technician and/or radiologist have reviewed the images. Once they are satisfied with the images, patients will be allowed to leave the scanning room and change back into their clothes, if necessary.

If a sedative was given, then patients are generally advised not to drive themselves from the testing site. Otherwise, patients can return to their regular daily routines. If they were given an injection and the injection site remains sore, they are encouraged to call their physician.

A computer is used to assemble the cross-sectional CAT scans into one three-dimensional image. A radiologist will interpret each of the final three-dimensional images and then send them with a report to the individuals on the patient’s care team, such as the surgeon, medical oncologist and radiation oncologist. In many cases, these specialists will want to view the images and patients may be asked to bring their records to the follow-up appointment.

The length of time to receive the results from the radiologist varies but a verbal report can usually be obtained within a day. Most patients will receive the results from the physician who ordered the CAT scan, often in their follow-up visit. Additional tests or treatment may be recommended depending on the results of the CAT scan.

Potential risks with CAT scans

Radiation levels used with CAT scans are higher than those used in regular x-rays. Although some patients are concerned about radiation exposure from a CAT scan, they should weigh the potential risks of the procedure against the potential life-saving benefits of the information gleaned from the scan. This is especially true with a deadly disease such as cancer in which early detection can improve the chances of survival.

In rare cases, a contrast solution used in a CAT scan may cause an allergic reaction in the form of mild itching or hives (small, raised reddened areas of skin). In more severe reactions, shortness of breath and swelling of the throat or other body areas may occur. Patients who feel any of these symptoms coming on during the procedure should immediately alert the healthcare professional performing the CAT scan.

Patients should inform their physician of the following: 

  • Pregnancy. A different study will likely be substituted to avoid the risk of exposing the fetus to radiation. In addition, women should inform their physicians if they are breastfeeding. They may be asked to wait 24 hours before resuming nursing if they were given a contrast medium.

  • Asthma or allergies. Contrast mediums can produce allergic reactions in some people, especially those with a history of asthma or allergies.

  • Other medical conditions. Certain medical conditions also may increase the likelihood of an untoward reaction to contrast mediums. These include diabetes, heart disease, kidney problems or thyroid conditions.

Treatments that may follow CAT scans

Patients who are diagnosed with cancer may receive a variety of treatments. In some cases, one form of treatment will be considered. In many other cases, a combination of treatments will be used to fight the cancer. Commonly used treatments include:

  • Chemotherapy. Uses one or more powerful drugs to target dividing cancer cells. Chemotherapy drugs aim to destroy cancer cells and to keep them from reproducing and spreading throughout the body.
  • Radiation therapy. Uses an energy called ionizing radiation to kill cancer cells and shrink tumors. Radiation targets dividing cancer cells and disrupts or destroys their genetic material. This process prevents the cells from continuing to grow and spread throughout the body. 

  • Biological therapy. Repairs, stimulates or enhances the immune system so that it can better recognize and destroy cancer cells. In some cases, biological therapy directly attacks cancer cells. This therapy is also used to blunt side effects associated with cancer treatments such as chemotherapy. 

  • Hormone therapy. Treatment for cancers that depend on hormones to grow and spread. Patients who undergo this treatment may take medications that reduce the levels of certain hormones, such as estrogen (in women) and testosterone (in men). In other cases, patients may take drugs that prevent cancer from attaching to hormones that help the disease to thrive.

  • Surgery. Used for the complete or partial removal of a tumor.

  • Bone marrow transplants. Replace bone marrow damaged by cancer or cancer treatments with healthy marrow obtained from the patient or a suitable donor. Bone marrow contains stem cells that produce red blood cells, white blood cells and platelets necessary for life.

Questions for your doctor regarding CAT scans

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor or other healthcare professional the following questions related to CAT scans:

  1. What is the difference between a CAT scan and traditional x-ray?

  2. How is a CAT scan different from an MRI?

  3. What type of CAT scan do I need?

  4. What do you expect to learn from the CAT scan?

  5. How should I prepare for my CAT scan?

  6. Where should I have the test done?

  7. How long will it take to complete the scan?

  8. Will I be given a contrast medium for the test? If so, what type?

  9. Can I request a sedative prior to the test?

  10. What will happen if I become anxious during the scan?

  11. If I am pregnant, what test can be used instead of a CAT scan?

  12. When and from whom will I receive the test results?

  13. How can I obtain my films to bring to my physician?

  14. Will I likely need additional tests?
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