A CT (computer tomography), sometimes called CAT scan, uses special x-ray equipment to transmit a pencil or fan-shaped x-ray beam as it rotates 360 degrees around your body. A digital computer together with a rotating x-ray device is used to create detailed cross sectional and/or three dimensional images or “slices” of body tissues and organs.
Imagine the body as a loaf of bread and you are looking at one end of the loaf. As you remove each slice of bread, you can see the entire surface of that slice from the crust to the center. The body is seen on CT scan slices in a similar fashion from the skin to the central part of the body being examined. When these views are added together, a three-dimensional picture can be obtained. CT imaging is particularly useful because it can show several types of tissue - lung, bone, soft tissue and blood vessels – with great clarity. With this clarity, radiologists can literally examine the body one narrow slice at a time. This makes diagnosing problems such as cancers, cardiovascular disease, infection, trauma, and muscle or bone disorders much easier. Unlike MRI, CT exams can be done even if you have a pacemaker or cardioverter.
Because it provides detailed, cross-sectional views of all types of tissue, a CT scan is one of the best tools for studying the chest and abdomen. CT scans are often used to guide biopsies and other minimally invasive procedures and to plan surgery. It is invaluable in diagnosing and treating spinal problems and injuries to the hands, feet and other skeletal structures. In case of trauma, CT scans can quickly identify injuries to the liver, spleen, kidneys or other internal organs. CT scans can also play a significant role in the detection, diagnosis and treatment of heart disease and vascular diseases that can lead to stroke and kidney failure. It is a very dependable tool in the cancer diagnosis process as well. It is also used in evaluation of head trauma and strokes (one of the most common uses) as well as for diagnosing appendicitis.
You should wear comfortable, loose-fitting clothing for your CT scan. Avoid clothing with snaps or zippers. The arrival time for your appointment will be based on the type of CT scan you are having. Some exams require that you drink a contrast material 1 to 2 hours prior to your exam. How you prepare also depends on which part of your body is being scanned. You may be asked to remove your clothing and dress in a hospital gown. You will also need to remove any metal objects such as jewelry that might interfere with the image results. If you are required to have a contrast material before your scan, it is usually to help emphasize blood vessels or other structures while blocking others. You will either have the contrast material by injection, mouth or enema. If your test involves contrast medium, your healthcare provider may ask you not to eat for a few hours before the test because the contrast medium can cause nausea. Depending on the part of your body being scanned, you may also be asked to take laxatives or enemas and temporarily modify your diet. If there is a chance that you may be pregnant, notify your healthcare provider and/or x-ray technologist.
- Have a known allergy to the contrast dye or material or any substance that contains iodine
- Have diagnosed heart failure
- Have diabetes and are on medication
- Have a history of kidney problems
- Become anxious in confined spaces or are claustrophobic
Most CT scans are conducted as an outpatient procedure. You have the test and then go home. A CT scanner looks like a large donut with a narrow table in the middle. The technologist begins by positioning you on the CT table. Your body may be supported by pillows to help you remain still and in the proper position during the exam. Once the exam begins, the table will move slowly into the round opening of the CT scanner while the x-ray tube rotates around your body. You may hear a clicking or buzzing sound as the table moves through the machine. Spiral or helical CT is used in most imaging centers. This technique has improved the accuracy of CT scans for many diseases. During a spiral CT, the x-ray machine rotates continuously around the body, following a spiral path to make cross-sectional pictures of the body. Due to the speed of the spiral CT, the entire body is usually able to be scanned during a single breath hold. The spiral CT provides higher-quality images with less radiation exposure than previous scans. This exam is particularly beneficial in a new vascular (related to blood vessels) imaging technique called Spiral CT angiography because it is non-invasive and allows doctors to see blood vessels without the need for more invasive studies.
Virtual colonoscopy is also a new technique that uses spiral CT. It allows doctors to see inside the colon without surgery or special instruments. There is now scientific evidence that spiral CT could even be beneficial for healthy people who are at the increased risk for developing diseases such as lung cancer or heart disease. However, these 2 tests are presently being offered at a select group of imaging centers on a investigational basis. The test itself is completely painless, but it is very important for you to remain motionless for the length of the study-which is typically brief. You will be alone in the room during the scan; however, the technologist can see, hear and speak with you at all times. The scan takes less than 5 minutes not including positioning and IV placement.
When your exam is over, you may be asked to wait until the images are reviewed to determine if more images are needed. Once that is established, you will be free to leave and go about your normal activities. If a contrast material such as barium was used during your exam, it is important that you drink plenty of liquid for 24 to 48 hours after your procedure to help you pass any barium that remains in your colon. Thirty two ounces in addition to your normal drinking habit is good, unless directed otherwise by your provider. You may also be asked to take a laxative following your procedure. Note that your stool may be white for a few days due to the barium. If you experience constipation, notify your healthcare provider.
CT scans do involve exposure to radiation in the form of x-rays, but the benefit of an accurate diagnosis far outweighs the risk. The amount of radiation received is about the same as the amount of background radiation the average person receives from the environment over a 3 year period.
A radiologist trained in reading CT images will study your films and report back to your referring healthcare provider who will in turn give the results to you. New technology also allows for distribution of reports over the internet at many facilities.
CT scans have vastly improved the ability of doctors to diagnose many diseases earlier in their course and with much less risk than previous methods. Further refinements in CT technology continue to evolve which promise even better picture quality and patient safety.