Contrast is a chemical substance used in imaging procedures to help show what is happening inside the body. There are a number of different ways that contrast may be used in a procedure.
Intravenous contrast is a clear iodine based liquid used to enhance solid organs and outline blood vessels that would normally not be seen well on a CT scan. This contrast will be given to you through an IV line usually placed in your arm. A powered injection pump is used to control the speed and amount of contrast in your procedure. The contrast will travel through your body via your blood vessels and then scans are taken. As the contrast travels through your body it may give you a warm flushed feeling, a metallic taste in your mouth or a feeling like you need to urinate. These feelings will pass in less than a minute. We will speak to you before we use intravenous contrast to confirm that you consent to its use. In cases where a patient is unable to give consent, we'll speak to a family member or Power of Attorney before using contrast in a procedure.
If you are a dialysis patient, there are certain circumstances were it is okay for you to receive IV Contrast. This will be discussed with you and your health care team before any procedure begins and you can speak with diagnostic imaging team about the risks versus benefits of intravenous contrast.
Oral contrast will be give to you to outline your gastrointestinal tract for certain CT scans. These contrasts will be used if your doctor suspects you have a perforation or anastomotic leak in your gastrointestinal tract. You will be given approximately 750 ml to 1000 ml of a solution to drink. As it takes time for the oral contrast to get through the intestines, it will be given over a one to two hour period before you begin your scan. The contrast can be diluted with water or another fluid such as juice, gingerale or baby formula and is generally colorless and tasteless. Crystal drink flavour packages can be added if you'd like.
Water is also used as an Oral Contrast. It is a negative contrast agent (it will show up dark on the CT Scan) and is especially useful when looking at the pancreas (for stones) and the gall bladder or their associated ducts. It is extremely rare for a person to be allergic to any of the oral contrasts used at KHSC. More information about allergies and reactions to contrast can be found below.
Rectal contrast will be used if we need to see your lower bowel more clearly. If rectal contrast is used the radiologist inserts a small tube into the rectum and slowly inserts the contrast. You will likely feel some mild cramping or discomfort as the bowel distends. The scan is done quickly after the contrast is administered and the contrast is then drained back into the bag after the procedure.
Allergies and reactions
Adverse reactions can sometimes occur following injections of contrast media, however most reactions are mild. Our staff will speak to you about the risks before any contrast is given to you. If you have had a mild allergic reaction in the past to this contrast, is unlikely that you will experience a similar or more severe reaction again. However, consideration should be given to the type and severity of your previous reaction. In most cases it is unnecessary to avoid further injections.
If you have multiple severe allergies or asthma, there is a small increased risk that you may have a reaction to contrast., however, these reactions tend to be minor. If you are allergic to shellfish, you do not have an increased risk for reaction. If you have had a reaction to the old contrast used before 1985, speak to your health care team. It is possible that you can safely receive one of the non-ionic, low-osmolality agents used today.
Please contact us or speak to your family physician with any specific questions around allergies and reactions not covered here.