Contrast agents for X-ray, CT and MRI

Contrast agents (otherwise known as contrast media or dyes) are chemical substances used within X-ray, CT and MRI to improve the quality of the images. Using contrast agents can help differentiate between structures in the body and its fluids, and also help to distinguish between similar looking organs.1 This allows the radiologist to more accurately report on any abnormality or disease present. The contrast agents temporarily enhance the images of the internal areas of your body that are being examined, and are later excreted through your urine or bowel movements.1

Contrast agents can be given using several methods:
  • Swallowed (given orally) – you may find the taste mildly unpleasant; however, most patients can easily tolerate it.1
  • Administered by enema (given rectally) – you can expect to experience a sense of abdominal fullness and an increasing need to expel the liquid. The mild discomfort should not last long.1
  • Given via an injection:
    • Intravenously (into a vein) or intra-arterially (into an artery), the needle may cause you some discomfort when it is inserted, and once it is removed, you may experience some bruising1
    • Intra-articularly (into a joint)2
    • Intrathecally (into areas such as the brain or spinal cord)
  • Through a catheter into the bladder
  • Into the cervical canal in order to examine a woman’s uterus and fallopian tubes

Contrast agents for MRI procedures take the following form:

  • Gadolinium-based contrast agents are useful for detecting lesions, tumours and vascular problems. They are mainly given intravenously (via a small needle in your arm that is similar to a blood test)1, but they can also be given intra-articularly if specific information about a joint is required.2

A radiographer, specialist radiology nurse or appropriately trained healthcare professional will administer the contrast agent prior to your scan; this will vary depending on the hospital you visit.

Please note: It is important to remember that preparation may be required for all of the above procedures; if you have not received any information prior to your appointment you should contact the hospital to confirm any such requirements.

  1. accessed March 2018
  2. accessed March 2018