Radiopaque

Anything that does not let X-rays or other types of radiation penetrate.

Radiopaque objects block radiation.

They are opaque to radiation.

A metal object, for example, is typically radiopaque.

If a child swallows a coin and it goes down into the stomach, it is easily visible in the stomach on an X-ray because it is radiopaque.

Radiopaque dyes are used in radiology to enhance the X-ray pictures of selected internal anatomic structures.

For example, an intravenous pyelogram (IVP) is an X-ray study of the kidneys using a radiopaque dye injected intravenously that highlights the renal pelvis (where the kidney collects urine) and the ureters (the two tubes, one coming from each kidney, that transport the urine down to the bladder).

Radiopaque is as opposed to radiolucent.

A radiolucent object permits the penetration and passage of X-rays.