Vocabulary for Contrast Medium in Medical Imaging

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  • 0:00 X-Rays & Contrast
  • 0:50 What Is a Contrast Medium?
  • 1:35 Radiopaque & Radiolucent
  • 3:00 Putting It All Together
  • 4:15 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Are you able to change the contrast on your computer screen? Sure you can! We can also change the contrast of the insides of your body! This lesson explains how.

X-Rays & Contrast

Take a look at the image on your screen right now.


What do you see?


If you said an x-ray or a bunch of black, gray, and white shapes and shadows, you're right.

What's in front of you is indeed an abdominal x-ray, and it is indeed a collection of black and white shapes, figures, and shadows. Sometimes, taking such an x-ray of the abdomen is enough to help diagnose a problem. Other times, it's not.

Here's what I mean. Have you ever seen an old photo that has been improved by changing its contrast? Stuff in the background or in the dark becomes clearer to the eye when the contrast is played around with.

Same thing here, the shadows of the x-ray image can be defined more clearly to aid in the diagnosis of something if we use a contrast medium when taking the x-ray.


We'll define what this is and its related terminology right now.

What Is a Contrast Medium?

A contrast medium, or contrast agent, is an internally administered substance used in radiography that has a markedly different opacity from surrounding soft tissue, one that's used to better permit the visualization of internal body structures.

Let's go over that definition a bit more clearly. First, this is an internally administered substance. By internally administered, I mean it's either swallowed by the patient or administered into the patient, such as by way of injection into a vein. In the latter case, we term this an intravenous contrast medium.

What kind of substances may these contrast media be? Well, some of the most common ones include barium, iodinated compounds, and air.

Radiopaque & Radiolucent

Okay, so let's go back to a normal picture example.


The picture shows a person in a field. The person is not transparent, yet the air around him is, right? In that case, the person is said to be very opaque while the air is translucent. Easy enough.

Now, look at the x-ray on your screen.


See the whiter areas of the x-ray?


They are opaque; we can't see through them to the other side very well. The proper term we use for this is radiopaque, a substance, such as bone and soft tissue, which doesn't allow x-rays to pass through very well, appearing whiter on the x-ray. 'Radio-' refers to 'radiation,' while 'opaque' means 'impervious to light,' which is itself electromagnetic radiation.

Bones are more radiopaque than soft tissue structures and hence appear whiter and more delineated in an x-ray when contrasted with a darker structure.

Now see the darker areas on the x-ray?


Those are properly termed radiolucent areas, substances, such as gas, which do allow x-rays to pass through quite easily, appearing darker on the x-ray. 'Lucent' means trans'lucent.' Easy to remember, huh?

Anyways, see that round, relatively dark, structure above the relatively white hip bone on this x-ray? That's a pocket of gas.

Putting It All Together

Okay, so now you know what a contrast medium is, and you know the basic terms behind the colors of the x-ray. Let's put this all together in one example.

Barium is a very radiopaque contrast medium. This means it will appear very white on a regular x-ray. Let's go back to our abdominal x-ray from before. You see how the intestinal contents in the middle of the screen are sort of wishy washy white or gray?


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