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Radiology: Cat Scans

What is a CAT scan?
A computed axial tomography (CAT or CT) scan is a test that uses x-rays to create pictures of the inside of the human body. The x-ray tube and its cameras (detectors) move around the body in a circle gathering information from different angles. This information is processed by a computer to create the final picture. Each picture is a cross-sectional image or slice of the inner organs of the human body. A stack of dozens, or sometimes hundreds, of pictures is produced for each scan. Any part of the body can be scanned with the abdomen, pelvis, chest, and head being the most common areas imaged. These pictures allow doctors to detect diseases that may not be obvious on physical examination. CAT scans are done for many reasons - such as looking for causes of headaches, belly pain, and breathing problems. For individuals with cancer, the CAT scan is used to determine how much tumor is present and whether it is responding to therapy. The scans are read by doctors specializing in this field who are called radiologists.

What does a CAT scan machine look like?
The CAT scan machine looks like a donut. It is circular with a hole in the middle through which a table passes. The table is like a narrow stretcher and is continuously moving throughout the scan, usually at a speed of a few millimeters per second. The table enters the machine, passes through it, and exits out the opposite end typically in a few seconds. Unlike a MRI, the machine is not like a tube and the person is not enclosed inside it. The length of the table that is in the machine at any given time is only a few centimeters.

How is a CAT scan done?
The CAT scan is performed by a CT technologist in the Radiology department. It is tailored to the part of the body that is being scanned. Contrast agents are given for certain types of scans. If the abdomen and pelvis are scanned, a contrast agent is usually given to enhance the information from the scan. First, an oral contrast agent is given to make the stomach and intestines bright on the scan. This contrast agent is either barium (a white liquid) or an agent with iodine in it. The iodine agent can be mixed with various juices for flavor such as strawberry or raspberry. A person is asked to drink 24-36 ounces of this liquid starting about an hour before the scan.

       The second contrast agent (dye) is for the blood vessels and organs of the body like the liver and kidneys. A needle is placed in the hand or arm to inject this agent into the veins and the injection is done during the scan. This contrast agent has iodine and is eliminated in the urine. Individuals may experience a warm sensation during the injection. The contrast agent is usually safe but some people may experience side effects or be allergic to it. Nausea is one possible side effect and therefore patients are asked not eat three hours prior to the scan. If you are allergic to a contrast agent with iodine you should let the technologist and your doctor know. Individuals with mild allergies may be given medicines starting a day before the scan. The contrast agent is also usually not given to people with certain medical conditions such as kidney failure. Informing your doctor and the radiologist about your allergies, prior contrast reactions, medical conditions, and medications is helpful prior to the scan.

       The CAT scan is done by having the individual lie on the scan table. Usually the person lies on their back but may be asked to lie on their stomach depending on the area being scanned. The arms are often raised above the head. The technologist may ask you to remove jewelry or metallic articles of clothing if they will be in the area scanned as they can create artifact on the images. Although you will be alone in the scan room, there is a microphone in the machine and the technologist can hear and see you through a glass window during the test. The intravenous contrast agent is injected and if your chest, abdomen or pelvis are being scanned, you will be asked to hold your breath during the test. Depending on the type of machine and body area being scanned, the length of time of the breath-hold can vary from less than 15 seconds to approximately 30 seconds. On the newest scanners, a scan from the top of the chest through the pelvis can be performed in 15 seconds. The table moves continuously through the machine during the scan. The entire test takes only a few minutes to perform.

Reading of the CAT scan:
In individuals with ovarian cancer, the radiologist looks for spread of disease beyond the ovaries. The location and size of the tumor masses in the abdomen and pelvis is given to the gynecologist. This information can be used to help plan the surgery and to decide if chemotherapy should be given before the surgery. After the initial surgery, CT, along with other tests, can be used to see if there is a recurrence of the tumor.

       The ovarian cancer itself usually appears as a large ovarian mass with cystic or fluid filled areas and solid areas. The solid areas can enhance or look bright with intravenous contrast. The tumor can spread into all areas of the abdomen and pelvis and appears as masses on the surfaces of the liver, spleen and intestines. These masses can be as large as several centimeters or as small as a few millimeters. Like the mass in the ovary, they look like solid areas of tissue or fluid filled areas. The lesions that are tiny can look like tiny spots in the fat over the bowel. Generalized fluid in the abdomen or ascites is also often present when the tumor has spread beyond the ovaries.

       Tumor can also spread to the lymph nodes causing them to increase in size. Masses can also be seen in organs such as the liver and lungs and there can also be increased fluid around the lungs.

For more information:
If you have any other questions or questions at the time of the study, speak to the CT technologist or the radiologist. Additional information can also be obtained from the American College of Radiology and Radiologic Society of North America combined website for patients - www.radiologyinfo.org.


  
     
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