Intravenous dye may be used in some imaging procedures (e.g., CT scan, MRI scan). Contrast dye is not used in all cases. Although rare, some patients suffer allergic reactions to the dye and newer contrast agents are quite expensive. However, there are times when dye is definitely needed, such as for detecting the spread of malignancy in the brain or liver. In situations where patients are allergic to contrast, MRI can be an excellent alternative to CT scan. The contrast used in MRI is different than the CT dyes, and the likelihood of a reaction is even more rare.
If the doctor and/or radiologist decides that a contrast scan is necessary, patients must be sure to mention any allergic history (especially to previous dye injections). They also should ask if the dye is absolutely necessary and if so, should request a newer, milder dye.
When Is a CT Scan Necessary?
The CT scanner has become the key player in the imaging arsenal. CT generally is not used in breast diagnoses, obstetrics, and in imaging of the various soft tissue structures that make up the joints. Other than those few exceptions, CT is most often the procedure of choice. Head CT has become a standard part of any work-up for conditions such as trauma; severe headache; prolonged, persistent headache; and changes in mental status.
Radiologists also perform fine needle aspirations and other biopsies under CT guidance, as well as under ultrasound guidance. In some medical facilities, the abdominal CT scan has become the preferred screening test for severe abdominal pain when kidney stones, appendicitis, or diverticulitis is suspected.
The CT study of the pulmonary arteries has become an important tool in the diagnosis of life-threatening pulmonary clots (emboli). The list of applications for CT seems to be growing daily.
CT Scan Risks and Potential Complications
The primary risk of a CT scan is radiation. If intravenous contrast is used, there is a risk for allergic reaction as well. Overall, the risks of CT are small.
What Actually Happens during CT Scan?
Prior to the study, a technologist or nurse interviews the patient. If intravenous contrast is not used, the test is very easy to take. Patients lie (usually on the back) on the CT table, which is often padded and concave to receive the body. Unless the patient has severe back pain while lying supine, or is severely claustrophobic, CT should not be an unpleasant experience.
Depending on the nature of the test, patients may be required to drink variable amounts of oral contrast prior to the procedure. Most of these preparations, although not delicious, are tolerable. Unlike many MRI gantries, the CT gantry is relatively open and only the most claustrophobic patients usually have a problem.
After CT Scan
If patients receive an oral contrast material, such as barium, they should be sure to drink plenty of liquids after the procedure. The oral dyes used for CT are much less dense than those used in the upper GI series, and the potential of impaction is much lower. Patients who receive IV dye should have no postprocedural problems. Delayed reactions are exceedingly rare.
Obtaining the results of the CT scan depend on many factors, including the urgency of the study, the seriousness of the condition, and the staffing in the radiology department. For urgent studies the results should be available quickly. If the test is performed early in the morning, results usually are available by late afternoon or the following day at the latest.
Can you ask the radiologist about his or her impressions right after the test? Often the radiologist is elsewhere and may not be available for an initial impression. Also, CT scans are very involved studies that require numerous images, may require reformatting, and may also require review of previous studies. There is a long way to go from raw data to diagnosis with CT scans, all of which may take a bit of time.