Computed tomography (CT)

1. What is computed tomography?
   Computed tomography (CT) is a diagnostic procedure that uses special x-ray equipment to obtain cross-sectional pictures of areas inside the body. A computer then assembles these pictures into detailed images of organs, bones, and other tissues. This procedure is also called CT scanning, computerized tomography, or computerized axial tomography (CAT).
   
   
2. How is CT used in cancer?
   Computed tomography is used in several ways:
• To detect or confirm the presence of a tumor;
• To provide information about the size and location of the tumor and whether it has spread;
• To guide a biopsy (the removal of cells or tissues for examination under a microscope);
• To help plan radiation therapy or surgery; and
• To determine whether the cancer is responding to treatment by getting smaller.
  
  
3. What can a person expect during the CT procedure?
   During a CT scan, the person lies very still on a table. The table slowly passes through the center of a large x-ray machine. The person might hear loud clicking or whirring sounds during the procedure. People may be asked to hold their breath at times, because breathing or other movement can result in blurred pictures.
   
   In some cases, a contrast agent, or “dye,” may be given by mouth, injected into a vein, or given by enema before the CT scan is done. The contrast dye can highlight specific areas inside the body, resulting in a clearer picture.
   
   Computed tomography scans do not cause any pain. However, lying in one position during the procedure may be uncomfortable. The length of the procedure depends on the size of the area being x-rayed; CT scans take from 15 minutes to 1 hour to complete. For most people, the CT scan is performed on an outpatient basis at a hospital or a doctor’s office, without an overnight hospital stay.
   
   
4. Are there risks associated with a CT scan?
   Some people may be concerned about the amount of radiation they receive during a CT scan. It is true that the radiation exposure from a CT scan can be slightly higher than from a regular x-ray. However, not having the procedure can be more risky than having it, especially if cancer is suspected. People considering CT must weigh the risks and benefits.
   
   In very rare cases, contrast agents can cause allergic reactions. Some people experience mild itching or hives (small bumps on the skin). Symptoms of a more serious allergic reaction include shortness of breath and swelling of the throat or other parts of the body. People should tell the technician immediately if they experience any of these symptoms, so they can be promptly treated.
   
   
5. What is spiral CT?
   A spiral (or helical) CT scan is a new kind of CT. During a spiral CT, the x-ray machine rotates continuously around the body, tracing a spiral path to make cross-sectional pictures of the body. This technique is under study as a screening method for lung cancer. Benefits of spiral CT include:
• It can be used to make 3-dimensional pictures of areas inside the body;
• It can detect small abnormal areas better than conventional CT; and
• It is faster, so the person is exposed to less radiation than with conventional CT.
  
  
6. What is virtual endoscopy?
   Virtual endoscopy is a new technique using spiral CT. It allows doctors to see inside organs and other structures without surgery or special instruments. One type of virtual endoscopy, known as CT colonography or virtual colonoscopy, is under study as a screening technique for colon cancer.
   
   
7. What is combined PET/CT scanning?
   Combined PET/CT scanning joins two imaging tests, CT and positron emission tomography (PET), into one procedure. A PET scan creates colored pictures of chemical changes (metabolic activity) in tissues. Because cancerous tumors usually are more active than normal tissue, they appear different on a PET scan.
   
   Combining CT with PET scanning may provide a more complete picture of a tumor’s location and growth or spread than either test alone. Researchers hope that the combined procedure will improve health care professionals’ ability to diagnose cancer, determine how far it has spread, and track patients’ responses to treatment. The combined PET/CT scan may also reduce the number of additional imaging tests and other procedures a patient may need. However, this new technology is currently available only at a very limited number of facilities.