What is Contrast Media?

Contrast Media (which is sometimes also referred to as contrast agent or dye) is a substance that is introduced into the body in order to improve the visibility of internal structures in diagnostic imaging techniques such as radiography, fluoroscopy, Computed Tomography (CT) Scan and Magnetic Resonance Imaging (MRI).

How does Contrast Media work?

Contrast agent applies the general principle of temporarily altering the contrast effect to a medical image in order to enhance visibility and improve detection of abnormality of internal body organs and structures that would not otherwise be demonstrable. The administered contrast agent flow through blood vessels, and perfuse into the targeted organ, or any suspected lesion or mass within the body. For example, it is not possible to identify blood vessels or to demonstrate the internal structure of the kidney without the use of contrast agent. The substance is later either absorbed by the body or eliminated through urine or bowel movements.

How is Contrast Media introduced into the human body?

• Injected through a blood vessel (intravenously)
• Swallowed (taken by mouth or orally)
• Administered by enema (given rectally)

Types of Contrast Media

• Iodine-based: Intravenously, and injected through vertebral disc and spine fluid space
• Barium sulphate: Administered by mouth and rectal
• Air: Usually used in combination with barium sulphate for imaging the colon
• Gadolinium-based: Intravenously in MRI

How safe is the use of Contrast Media?

Contrast agent is considered a safe drug. It’s use does have a slight risk of causing an allergic or adverse reaction which can range from mild to severe, though severe reactions are uncommon. Hence, before undergoing any contrasted imaging examination, it is very important for the patient to inform the doctor of any known medical history of:

• Asthma
• Allergy to iodine (derived from seafood or drugs)
• Allergy to any kind of food
• Allergy to any medication
• Dehydration
• Heart disease, diabetes and kidney disease
• Previous history of adverse reaction to contrast media

Patients with the above conditions are at a higher risk for adverse reaction to contrast agent. They are usually prescribed medication (steroids) to be taken before the examination to lessen the risk of an allergic reaction.

Adverse Reaction from Contrast Media Administration

Adverse reactions after the administration of iodine-based contrast media can be any of the following:

• Flushing
• Nausea
• Vomiting
• Headache
• Itching
• Skin rash
• Difficulty in breathing (shortness of breath)
• Swelling of the throat

Adverse reactions after the administration of oral contrast media include:

• Constipation
• Stomach cramps
• Vomit
• Diarrhoea
• Hoarseness
• Agitation
• Itching
• Difficult breathing and swallowing

Pregnancy

Pregnant women need to inform the radiologist or radiographer about their pregnancy or of any possible pregnancy. Contrast media administration is usually avoided to minimise risk to the baby. Other imaging modalities will then be considered.

Breast-feeding mothers

Breast feeding mothers are advised to discuss with their doctors if undergoing any examination requiring administration of contrast agent.

Patient with impaired kidney function

Patients with impaired kidney (renal) function will be given special consideration before being administered contrast agent.

References

1. ESUR Guideline on Contrast Media. Available at: http://www.esur.org/guidelines/
2. Manual on Contrast Media, Edition 7.0, 2010: 33-35. American College of Radiology