What is Contrast Material

What is Contrast Material?

If you have ever undergone medical imaging, such as an MRI or CT scan, you have probably heard of contrast material. 

MRIs (magnetic resonance imaging) and CT (computed tomography) are types of medical equipment that creates images of internal organs and structures. Contrast material enhances and improves the quality of these images. Contrast material can also improve the quality of some ultrasounds and x-rays. In many cases, the use of contrast can help the radiologist distinguish normal from abnormal conditions. 

How are contrast materials used? 

​​Contrast materials enter your body in one of three ways for the test:

  • By mouth
  • Rectally, by enema
  • Injected into a blood vessel 

Following the imaging exam, your body either absorbs the contrast material or eliminates it through urine or stool. The contrast is not permanent, so it will not discolor your organs forever.

Not all imaging tests require the use of contrast materials, as today’s advanced technology already produces sharp and clear images. Your doctor will specify whether your MRI or other imaging test is with or without contrast. In some cases, doctors request the imaging tests be done with and without contrast.

Contrast side effects

The particular type of contrast dye used in an MRI scan is different to other x-ray based tests. In MRI, the contrast used contains a naturally occurring substance called Gadolinium, which is typically attached to other compounds so that it can be used in the human body without causing any harm. 

Gadolinium contrast medium is generally very safe. Side effects or reactions are uncommon but can occur and are not long-term.

The most common reactions to MRI contrast material are:

  • Headache
  • Nausea
  • Brief dizziness
  • Coldness at the injection site

Types of contrast materials

There are three broad kinds of contrast available: intravenous (IV), oral (PO), and rectal (PR). 

  • Intravenous contrast

Intravenous contrast is used in CT to help highlight blood vessels and to enhance the tissue structure of various organs such as the brain, liver, and kidneys. “Intravenous” means that the contrast is injected into a vein using a small needle. Some imaging exams of the abdomen and gastrointestinal system use both the intravenous iodine and orally administered barium contrast for maximum sensitivity.

The intravenous CT contrast is clear like water and has a similar consistency. It is typically packaged in a glass bottle or vial. A sterile syringe is used to draw it from the bottle or a power injector is used to administer the contrast. The amount of IV contrast used depends upon the patient’s age, weight, the area being imaged, and heart health.

Sometimes it is necessary to not drink anything for an hour to several hours before the exam. The preparation time varies depending on the actual exam as well as the imaging center’s requirements. Always ask your doctor and the imaging staff where the exam is scheduled for exact guidelines. 

  • Oral Contrast

Oral contrast is often used to enhance CT images of the abdomen and pelvis. There are two different types of substances used for oral CT contrast. The first, barium sulfate, is the most common oral contrast agent used in CT. The second type of contrast agent is sometimes used as a substitute for barium and is called Gastrografin.

Barium contrast medium looks like and has a similar consistency as a milkshake. It is mixed with water and depending on the brand used, may have different flavors (for example, strawberry or lemon). Gastrografin contrast is a water-based drink mixed with iodine and has a tinted yellow color. When given orally, gastrografin may taste bitter.

If you are instructed to take oral contrast for CT, it is important to eliminate as much food as possible from the stomach and intestines before your scan. Food and food remains can mimic disease when the oral contrast is present. Not eating and/or drinking for several hours before the CT exam is required. The preparation time varies depending on the actual exam as well as the imaging center’s requirements. Patient preparation varies from center to center, depending on a number of issues. Some types of oral CT contrast are taken at home well before the CT examination.

  • Rectal Contrast

Rectal contrast is often used to enhance CT images of the large intestines and other organs in the pelvis. There two types of substances used for rectal CT contrast (barium and Gastrografin) are the same as the type used for oral CT contrast, but with different concentrations. The first, barium sulfate is the most common rectal contrast agent used in CT. The second type of contrast agent is sometimes used as a substitute for barium and is called Gastrografin.

Rectal CT contrast is usually given using an enema where a small plastic tip is inserted into the rectum while a patient lies on their side. This tip is connected to a bag filled with the barium or gastrografin contrast through a tube.  After the tip is inserted, the patient lies flat and the bag is raised above head level to allow the contrast to fill the lower intestines.  During this filling phase, the patient may feel mild discomfort, coolness, and generalized fullness.  It is important to relax as much as possible during this phase until the CT scan is complete.

Like oral contrast, it is important to eliminate as much food as possible from the stomach and intestines before your scan.To book a scan, visit us at Medmo.com. Medmo helps people schedule radiology imaging tests – such as MRI, CT scans, PET, and more – at nearby accredited centers and identify the payment solution that works best for them.

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