Computed Tomography (CT/CAT)
Computed tomography (CT) (sometimes called "computerized tomography" or "computed axial tomography" (CAT)), is an X-ray exam that uses specialized equipment to produce cross-sectional images of the body. Each cross-section represents a “slice” of the part of the body being imaged. When viewed together these images provide a comprehensive view of the area, with greater clarity and more detail than conventional X-ray images. Using special software, three-dimensional images can be made from the individual slices of a CT scan.
Doctors use CT scans of internal organs, bones, soft tissue, and blood vessels to:
- Diagnose disease, trauma, or abnormalities
- Plan and guide surgical, interventional or other therapeutic procedures
- Monitor the effectiveness of therapy for diseases such as cancer and infection
A CT imaging system includes a scanner shaped like a donut, and a motorized table that slides in and out of the opening in the scanner. You will lie on the table and while inside the scanner, an X-ray source and a detector assembly opposite the source will rotate around the table. During a single rotation, which takes about a second, a fan-shaped beam of X-rays passes through a section of your body and is registered by the detectors opposite. The scanner collects images from many different angles during a complete rotation; these are sent to a computer, which reconstructs all of the individual "snapshots" into one or multiple cross-sectional images (slices) of the internal organs and tissues. For some CT exams we will give you a contrast agent ("dye") intravenously and by mouth to make the organs and structures more visible in the images we create.
How do I prepare for the test?
Intravenous contrast, sometimes called dye, is administered for many CT scans. If this is the case, you will be required to fast for four (4) hours before your CT scan. No food or liquids should be taken during that time, and your physician will advise you about taking medications during the fasting period. If your abdomen or pelvis is being scanned, you may need to drink a flavored liquid that allows better visualization of the gastrointestinal tract. If this is the case, you will be asked to come to the office prior to your test to drink one to two bottles of this liquid. You must drink the first one an hour before your procedure, and the second bottle 30 minutes before. Once your CT scan is completed, you may resume your normal diet, but it will be necessary to increase the amount of fluids/water you drink for several hours.
On the day of the test you should wear comfortable clothes, and you may be asked to change into a gown when you arrive at the CT exam site.
What will happen during the test?
A CT exam is usually painless and quick. If your doctor has requested that you have a CT scan with contrast, we will first insert an IV, usually into your arm.
We will then take you to the CT exam room, and position you on the CT table, usually on your back. When the table slides into the scanner a red light may shine on your body, which helps ensure that you are properly positioned. We use the most up-to-date CT scanners, which make only slight buzzing and clicking sounds as the scanner revolves around you. The CT technologist will leave the room to perform the scan, but he/she will be able to see, hear, and speak with you at all times. During the IV injection of contrast, you may feel a warm, flushed sensation and may have a mild unpleasant taste in your mouth for a few minutes.
The technologist will ask you to hold very still and may ask you to hold your breath during the scan. Any type of movement during a CT scan will make the images look blurry and may cause the scan to have to be repeated.
The scan will take between 5 and 15 minutes to complete.
Are there any risks?
CT exams use higher radiation doses than conventional radiography because the CT image is reconstructed from many individual X-ray projections. If the exam is medically necessary the risk is quite small compared to the benefit of an accurate diagnosis or intervention. Some people may have an allergic reaction to the intravenous contrast agent, or dye.
After the test
After the exam you can immediately resume your normal activities.
A radiologist will analyze the CT images and communicate the results to your health care provider who requested the exam. Your health care provider will then discuss the results with you.