Webster's New World Medical Dictionary

radionuclide scan
An exam that produces pic-
tures (scans) of internal parts of the body based
upon the presence of radioactive material. The
patient is administered a small amount of radioac-
tive material. A machine called a scanner then
measures the radioactivity in certain organs.
radiopaque
Opaque to one or another form of
radiation, such as X-rays. Radiopaque objects block
radiation rather than allow it to pass through. Metal,
for instance, is radiopaque, so metal objects that a
patient may have swallowed are visible on X-rays.
Radiopaque dyes are used in radiology to enhance
X-ray pictures of internal anatomic structures. The
opposite of radiopaque is radiolucent.
radiosensitive
Sensitive to X-rays and other
forms of radiant energy. For example, if a tumor is
radiosensitive, it is potentially treatable with radia-
tion therapy. The opposite of radiosensitive is
radioinsensitive.
radiotherapy
See 
radiation therapy.
radium
The radioactive element discovered by
Marie and Pierre Curie in 1898. Since the discovery
of radium, many radioactive isotopes have been
used for both the diagnosis and the treatment of 
diseases.
radius
The smaller of the two bones of the fore-
arm, located on the thumb’s side. (The larger bone
in the forearm is the ulna.)
radon
A radioactive element that is formed, as a
gas, during the breakdown of radium. Radon expo-
sure is the second leading cause of lung cancer
deaths in the United States, after smoking. Radon
gas continuously seeps into the air from uranium-
and radium-bearing soil and rock. Well water can
be contaminated with radon and may carry radon
into a house through the water pipes. There are sev-
eral radon testing devices on the market.