What is CT imaging and how does it work?
Since the 1970s, Computed Tomography (CT), also called Computerized Axial Tomography (CAT), scans have been used to create three-dimensional images of the body. CT imaging is a noninvasive technology that quickly and painlessly helps doctors diagnose and treat medical conditions such as pancreatic cancer. A CT scanner uses special x-ray equipment to take multiple image “slices” of the inside of the body. A computer compiles the x-ray images to create a series of detailed cross-sectional pictures of the area being studied. The images can then be analyzed on the computer monitor or printed.
A CT scan is one of the most common imaging procedures performed when an individual is suspected of having pancreatic cancer. The images are often used to determine whether the tumor can be surgically removed.
A contrast dye may be given orally or injected into a vein (by IV) to show small tumors of the pancreas and whether the cancer has spread.
Why is CT imaging used?
Unlike a basic x-ray image which shows only bone, CT images show bone, soft tissue and blood vessels. Because of this unique ability to show details of all types of tissue, CT scans are often used to look for tumors in soft tissues such as the pancreas. In pancreatic cancer, CT scans are used to:
- detect the presence of a tumor.
- provide pictures to determine the size and location of a tumor and whether the tumor has metastasized, or spread to other tissues.
- guide a biopsy. The removal of cells or tissue from the tumor for examination is called a biopsy and is the only way to determine the exact diagnosis regarding the specific the type of pancreatic tumor.
- help plan for surgery or radiation therapy.
- determine whether the tumor is responding to treatment.
What are the different types of CT scans?
Conventional CT: An x-ray beam is directed at several different angles and levels in the abdomen. The x-ray is flashed on and off quickly as it takes images of the inside of the body. A computer processes the images into approximately ½-inch cross-sectional slices of the abdomen.
Spiral or helical CT: The x-ray bean remains on continuously, unlike the conventional CT. In a spiral CT, the x-ray beam rotates around the patient, in a spiral pattern, as the patient lies on a slowly moving table. Many computed tomography machines are now spiral or helical CT scanners. The spiral CT is faster and produces more detailed three-dimensional images than conventional CT images. Where available, spiral CT is preferred over conventional CT for detecting and staging pancreatic cancer. Spiral CT is useful in staging because it provides more anatomic detail that can show if the tumor is involved with nearby blood vessels.
Combined Positron Emission Tomography (PET)/Computed Tomography (CT): PET/CT scanning combines two imaging tests into one procedure. The PET scan produces images by detecting tissues that are using more glucose, the body’s basic fuel. Since cancer cells use glucose at a faster rate than normal cells, tumors may appear different on PET images. By combining the PET and CT scans, a more complete picture of the tumor may be obtained than by either exam alone. The combined PET/CT scan may provide doctors with more information about the location of the tumor and whether it has grown or spread. This combined technology has only been around since 2000 and is not available at all medical facilities. Individuals should ask their health insurance provider if the combined PET/CT scan is covered by insurance.
What should I do to prepare for a CT scan?
The healthcare team will give the patient exact instructions before a CT procedure. In general, the patient should wear comfortable, loose-fitting clothing to the appointment. If possible, leave all metal objects, including jewelry, eyeglasses, dentures or hair clips at home as they will need to be removed during the procedure. The radiation technician may provide a gown to wear during the actual scan.
If a contrast dye will be used, the patient may be asked not to eat or drink anything for several hours beforehand. Be sure to inform the doctor of any allergies. The doctor will tell the patient whether to continue taking regular medications before the CT scan.
What happens during a CT scan?
The patient may be given a contrast dye, by mouth or by IV, before or during the CT procedure, which will help make the organs more visible on the final images. The radiation technologist then positions the patient on the CT exam table usually lying flat on his/her back, although it can be done with the patient on their side or stomach. The patient will be asked to hold very still during the CT scan. Pillows or straps may be used to help the patient stay in the correct position throughout the exam.
The technician controls the CT examination from a control room next to the CT room where he/she can see, hear and talk to the patient. Through an intercom, the technician may instruct the patient to remain still and possibly to hold his/her breath for a few seconds.
The table will move through the scanner to determine the correct starting position for the scans. Then, while the CT scan is performed, the table moves slowly through the machine while the donut-shaped CT scanner rotates around the body taking x-ray images. Depending on the model of CT scanner, there may be some noise associated with the rotating x-ray beam.
A CT scan usually lasts between 15 and 60 minutes.
What can I expect after a CT scan?
After the CT scan is completed, the radiation technologist will ensure that high quality images were obtained before helping the patient from the exam table. Most CT scans are painless.
For individuals who are claustrophobic, a doctor or nurse may offer a mild sedative to help keep the patient calm. If a sedative is used, the patient should not drive a vehicle and should plan ahead to have a family member or friend drive them to and from the exam.
It may take several days to learn the results from a CT scan.
What complications can occur with a CT scan?
CT scans are not painful and have very few associated risks. There may be some discomfort from having to remain still for several minutes.
If a contrast material is injected, the patient will feel a slight pin prick and may feel warmth in the area where the needle enters the vein. If the contrast substance is given by mouth, the patient may find the taste unpleasant for a few minutes. In rare instances, patients are allergic to contrast dye in which case alternative imaging tests must be used. Symptoms of a mild allergic reaction include itching and hives, or small bumps on the skin. A more serious allergic reaction may include shortness of breath and swelling of the throat or other parts of the body. The patient should notify the technician immediately if he/she experiences any of these symptoms during or after the CT procedure.
In rare cases, pancreatitis, infections, surgeries or other diseases may change the way cells use glucose. This may produce false results on PET images.
Since CT scans use x-rays, patients and doctors may be concerned about the repeated exposure to radiation when CT is used for screening and surveillance.
Information provided by the Pancreatic Cancer Action Network, Inc. (“PanCAN”) is not a substitute for medical advice, diagnosis, treatment or other health care services. PanCAN may provide information to you about physicians, products, services, clinical trials or treatments related to pancreatic cancer, but PanCAN does not recommend nor endorse any particular health care resource. In addition, please note that any personal information you provide to PanCAN’s associates during telephone and/or email communications may be stored and used to help PanCAN achieve its mission of assisting patients with, and finding cures and treatments for, pancreatic cancer. Stored constituent information may be used to inform PanCAN programs and activities. Information also may be provided in aggregate or limited formats to third parties to guide future pancreatic cancer research and treatment efforts. PanCAN will not provide personal directly identifying information (such as your name or contact information) to such third parties without your prior written consent unless required or permitted by law to do so.