CONTRAST AGENTS (DYE) IN RADIOLOGY

Certain radiological exams require a special medication called as “dye” or “contrast agents”. These are “Imaging-related medications” and are designated as “prescription drugs” in accordance with Food and Drug Administration (FDA).  

Contrast helps certain areas to show up better and highlight tissues and organs that would not be visible otherwise. This allows the radiologist to distinguish normal from abnormal conditions. 

A simple example would be: difference between a color and black &white picture.  A color picture has more details and much more information can be extracted (see fig. 1 a and 1 b). 

Fig. 1a: B& W picture of sunset                       Fig. 1b: Color picture of sunset

Similarly, when introduced into the body prior to an imaging exam, contrast materials make certain structures or tissues in the body appear different on the images, then they would appear, if no contrast material had been administered. Fig. 2 b shows, a tumor in the abdomen (red arrow). It is easily identified after giving contrast during a CT scan if compared to fig. 2 a. 

Fig. 2a: Non contrast CT                         Fig. 2b: Contrast CT shows tumor (red arrow).

Administration of dye, causes organs and tissues to show up better and allowing them to stand out. Thus "contrast selected areas" of the body are easily distinguished form other surrounding tissues. This leads to improved visibility of specific organs, blood vessels or tissues. This helps a radiologist diagnose medical conditions so that treatment can be started early by your physician.   You foresee a problem, before it manifests!

There are different types of contrast agents used for various imaging procedures like:

1.      Barium is used for study of intestine like in barium follow through for small intestine.

2.      Iodinated contrast agents administered for IVP (intra venous pyelography) or CT scan.

3.      Paramagnetic agents like gadolinium administered during MRI.

These contrast agents can be given through different routes like:

1.      Orally or rectally for barium procedures.

2.      Injected through a vein or artery.

3.      Injected into a body cavity under image guidance.

Contrast Radiography helps answer important questions about the health and functioning of vital organs. The phenomenon of present-day radiologic imaging would be lacking without these agents.

References:

1.      http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_contrast

2.      http://www.hillcrestcushing.com/contrast-radiology

3.      Jill M. Widmark, Imaging-related medications: a class overview. proc (bayl univ med cent). oct 2007; 20(4): 408–417. pmcid: pmc2014815.