CT scans and other x-rays are monitored and regulated to provide the minimum amount of radiation exposure needed to produce the image. CT scans provide low levels of ionizing radiation which has the potential to cause cancer and heritable defects. The risk associated with any individual scan is small; however, the risk increases as numerous additional studies are performed.

During pregnancy, an abdominal CT scan is usually not recommended, due to risk to the exposed fetus, including developmental malformations and childhood cancers. Patients who are or may be pregnant should speak with their health care provider in order to first take a pregnancy test or choose an appropriate alternative imaging modality without risk to the fetus, such as ultrasound.

The most common intravenous contrast dye is iodine based. A person who is allergic to iodine (such as those with seafood allergies) may experience nausea, sneezing, vomiting, itching, or hives. If contrast administration is essential for a patient with any of the prior reactions, the health care provider may choose to pre-medicate the patient before the scan with a short course of immune-suppressing steroids and/or Benadryl. Alternatively, other contrast media or other imaging modalities (such as ultrasound or MR) may be used.

Rarely, the dye may cause anaphylaxis (a life-threatening allergic response), usually manifested by swelling in the airway. The patient is instructed prior to the scan to notify the technologist via the intercom if he/she has difficulty breathing. If such a rare reaction does take place, the exam will be stopped, and the patient will be rapidly treated with special medication and closely monitored by a physician.

Iodine-based contrast is primarily filtered out of the bloodstream by the kidneys, and thus patients with diabetes or renal disease will require continuous hydration and close monitoring of kidney function. Diabetics on certain a glucose-lowering medication (glucophage/metformin) and renal dialysis patients should speak with their physician regarding stopping the medication, and the proper scheduling of the scan in conjunction with dialysis, respectively. Consent from the patient or designated guardian must be obtained prior to the use of intravenous contrast.

For additional information regarding why the test is performed and normal and abnormal results, please see the specific CT topics:

• orbit CT scan
• cranial CT scan
• lumbosacral spine CT scan
• thoracic CT scan