Webster's New World Medical Dictionary

radioactive iodine
A version (isotope) of the
chemical element iodine that is radioactive.
Abbreviated RAI. RAI is used in diagnostic tests as
well as in radiotherapy of the thyroid. It may be used
in the treatment of hyperthyroidism and cancers of
the thyroid. It directly radiates thyroid tissues,
thereby destroying them. RAI should not be used
during pregnancy and breastfeeding. See also
Graves disease.
radioactive tracer
A radioactive molecule that
can be sent through the body’s circulatory or uri-
nary system, with its progress followed by a radia-
tion-sensitive machine.
radioallergosorbent test
See 
RAST.
radiograph
In medicine, an X-ray or a film pro-
duced through X-ray.
radiography
The process of obtaining film
records (radiographs) of internal structures of the
body. Radiography is made possible by X-rays pass-
ing through the body to act on a specially sensitized
film.
radioimmunoassay
A very sensitive, specific
laboratory test (assay) that uses radiolabeled and
unlabeled substances in an immunological (anti-
body-antigen) reaction.
radioinsensitive
Not sensitive to X-rays and
other forms of radiant energy. For example, if a
tumor is radioinsensitive, it cannot be successfully
attacked by using radiation therapy. The opposite of
radioinsensitive is radiosensitive.
radioisotope
A version of a chemical element
that has an unstable nucleus and emits radiation
during its decay to a stable form. Radioisotopes
have important uses in medical diagnosis, treat-
ment, and research.
radiologic
Having to do with radiology.
radiologist
A physician who specializes in radiol-
ogy, the branch of medicine that uses radiation for the
diagnosis and treatment of disease. A radiologist can
subspecialize and become, for example, a radiation
oncologist or an interventional radiologist. See also
radiation oncologist; radiologist, interventional.