CT is a diagnostic imaging procedure that uses X-rays and detects disorders and disease in muscle, bone, soft tissue, organs and vessels. Unlike conventional X-ray, which uses a stationary X-ray machine to produce a two-dimensional image much like a photograph, a CT scan uses an X-ray tube and receptors rotating around the patient and a powerful computer to create cross section images across your body in any plane.
Depending on the type of scan you are having and the preparation needed your exam can take anywhere from 10 minutes to an hour. Some factors attributing to the time needed include: starting an IV for IV contrast administration, oral contrast administration, diagnosis, patient’s ability to hold still, delays needed for normal body processing and uptake of the IV contrast. During the scan you will lay on a padded table, which will be raised then moved in and out of a doughnut-shaped machine. You will lie on your back, side or stomach depending on what area you are having scanned. The table will move in and out of the machine several times quickly, this is used to get a basic image for positioning slices.
Breathing instructions will be given before each scan is done. It is important to pay attention to the verbal breathing instructions as they are not always the same. During the actual scan the table will move slowly through the scanner while images are obtained. Lying as still as possible throughout these scans is very important because any movement or repositioning can cause motion on images or anatomy to be missed on the scan. During some scans contrast may be injected into an IV in your vein, this contrast helps highlight any tissues that get blood flow and also will get picked up by your kidneys, so on abdominal scans delayed scans will be taken to show kidney and bladder function. After the scan is complete the CT staff will check the images for motion and proper positioning and inclusion of all anatomy before getting patient off of the table. It is important to note that the CT staff will be watching the patient and communicating with the patient throughout the exam by intercom. After the images are checked and the patient is evaluated for any adverse reaction to any contrast given the patient will be helped up and given instructions for the rest of the days’ activities.
Contrast sometimes referred to as “dyes” are used to highlight organs, tissues and blood vessels. They can help the radiologist determine the presence and extent of injury or disease by increasing the visibility of all the structures of organs and tissues being examined. There are three main types of contrast for CT’s:
When either oral contrast is used the patient will usually drink about 1,000 to 1,500 cc, the equivalent of 3 to 4 12-ounce drinks.
Usually an hour to two hour prep time is needed for oral contrast to work its way through the GI system. This being the case, many patients pick up there contrast the day before their CT at any campus in Imaging or their doctors office and follow prepping instructions given.
IV or Intravenous contrast is used to highlight organs and tissues and vessels throughout the body. Iodine is the most common IV contras.
During injection it is common to feel a warm sensation or hot flash throughout the body and this is sometimes accompanied by a metallic taste or smell and a sensation of a rush to your bladder or urgency to urinate. Contrast administration is done at a certain time during exams and scans are sequenced after injection to view uptake and disposal. After the exam is completed your kidneys and liver quickly eliminate the contrast from your body.
Rectal contrast is used to highlight the large intestine and the lower GI system, and is administered through an enema.
Both barium and iodine can be used as rectal contrast.
When rectal contrast is administered the patient might experience mild discomfort, coolness and a sense of fullness, sometimes a cramping sensation will also accompany this sensation. After the procedure is complete the contrast is drained and the patient may use the restroom. The preparation for rectal contrast administration includes fasting for several hours and the use of a cleansing enema the night before the procedure to cleanse the colon.
As with any medicine, contrast or substance injected or injected there is a risk of allergic reaction to contrast. If you have any change in how you feel, difficulty breathing, hives or itchiness after having contrast administered, it is very important to tell the CT staff.
Comfortable loose fitting clothing should be worn for your exam. A gown will be provided if clothes have any artifacts on them that will interfere with imaging such as metal buttons and clasps. Metal objects, jewelry, dentures, hearing aids, and hair pins may have to be removed depending on there location to the area of interest. Depending on the type of study you will be having you may be given instructions before your exam on what you can eat and/or drink before your exam, this is especially true when contrast will be used during the scan. Women who are pregnant or think they may be pregnant need to inform both their doctor and the technologist before having the CAT scan. This needs to be discussed with your doctor to make sure the benefits will outweigh the possible risk to your baby. Always provide the CT staff with a list of any medications you are taking and a list of all food or drug allergies. Certain medications will need to be held for 48 hours after a contrast injection.
CAT scan results are interpreted by a radiologist who is a physician trained to supervise and interpret radiological examinations. The radiologist will analyze all the images taken during your exam and send a signed report to the ordering physician this will take 24 to 48 hours, additional copies can be sent upon request to primary care physicians or specialists. The ordering physician or your primary care physician will go over the results with you.