The Truth About Contrast In Radiology

One of the most common questions asked by my patients is about contrast. Contrast is used in radiology to outline body parts to provide greater detail to detect disease. Generally, there are two types of contrast--oral contrast and intravenous contrast. Oral contrast is ingested by the patient. Intravenous contrast is injected into the patient’s veins. Both are of great value in making diagnoses. Here are some of the more common questions asked about contrast:

Q) What is oral contrast? Why do I have to drink it before the examination? 
A) Oral contrast is a white colored liquid which contains barium. This solution looks white on x-rays and CT scans. It allows the radiologist to distinguish what is bowel and separate that from potential disease (such as tumor or infection). Oral contrast is safe to drink for almost all patients. 

Q) What is intravenous (IV) contrast? 
A) Intravenous contrast is a solution that is injected into the vein given for both CT and MRI tests. IV contrast in CT is a non-ionic iodine based liquid. IV contrast for MRI is a gadolinium based liquid. Both types of IV contrast have the same function. First, the contrast makes the vessels look bright and can be used to evaluate blood vessels and look for blot clots. Second, it also is taken up by our organs and taken up by cancer. It better defines if there is a hidden mass in our organs. Depending on how the mass takes up the contrast, a radiologist can better decide whether something is a malignant tumor or is benign. 

Q) If contrast is so helpful, why are some of my examinations ordered without contrast? 
A) Whether you need contrast will depend on what your doctor is looking for and concerned about based on your symptoms. For example, if your doctor is searching for cancer or infection, contrast is usually required. However, contrast is not necessary for a CT scan that is looking for kidney stones or brain injury. Generally, an MRI of the spine that is looking for a cause of back pain will not require contrast. Your doctor and the radiologist will work together to determine whether it is appropriate for you to receive contrast.

Q) Why is it important to check my kidney function before having contrast? 
A) Both MRI and CT contrast are filtered from your body through the kidneys. Therefore it is important to be sure the kidneys function well enough to remove the contrast. At my office, we routinely screen patients who are older than 65 years old and/or have diabetes for adequate renal function before giving contrast. All patients are encouraged to drink lots of water for several days after an examination with IV contrast to be sure the contrast is thoroughly flushed from your system. QI have heard about allergies to the intravenous contrast. 

Q) Is it safe? 
A) In general, allergic reactions vary among people. For example, a peanut allergy can vary from a little itching to hospitalization. It has been reported that up to 8% of people receiving IV contrast could have an allergic reaction. Most of these reactions are mild, and include a feeling of warmth, hives, itching, nausea and vomiting. These reactions are easily treated with Benadryl. Severe, life-threatening reactions, including anaphylaxis, are extremely rare and occur in 0.1% of people receiving contrast. At my facility, a physician is always a few steps away from each patient receiving IV contrast and has a large assortment of medications at his disposal for quickly treating any potential complications.

Q) I am allergic to shellfish. Can I still receive intravenous contrast? 
A) There is a myth that patients that are allergic to shellfish are allergic to the iodine contained within shellfish and therefore would be allergic to the iodine containing IV contrast. This is untrue. Iodine allergy is a myth. Iodine is found within all of our thyroid glands. It is also in table salt. A shellfish allergy is caused by a muscle protein called tropomyosin. A person with a shellfish allergy has no more risk of being allergic to IV contrast as they do of being allergic to fruit or eggs.