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Nuclear Medicine
Name: Reuben G.
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 2001-2002
Question:
How does the nuclear medicine equipment work?
Replies:
Dear Reuben-
The principal business of a Nuclear Medicine department is the formation of
medical images using a device called a gamma camera. Perhaps you are
familiar
with medical x-ray images? A gamma camera is sensitive to gamma rays. Gamma
rays are very similar to x rays. They can have the same wavelengths and
energies. The only difference is that x rays are produced by the
acceleration
of electrons whilst gamma rays are emitted from the nucleus of an unstable
atom
which is undergoing radioactive decay. Another important difference is
that x
rays pass through a patient's body and cast a shadow on a sheet of film. The
light and dark areas on the film correspond to regions of different physical
density in the patient's body. Bone contains denser elements than soft
tissues,
so bone absorbs more x rays than the soft tissues. Wherever the x rays
strike
the film, it turns dark. Since not many x rays pass through bone, those
areas
of the film do not get very dark. That is what causes light bone images to
appear against a dark background on x-ray films.
In typical Nuclear Medicine imaging, a radioactive substance is injected into
the patient's bloodstream. The amount of radiation is small so there is very
little risk of causing harm to the patient. The substance is carefully
chosen
so it will concentrate in a region of disease. For example, it might be a
substance that attaches to cancer cells. When the patient is placed in
front of
the gamma camera, an image is formed of the pattern of the radiation being
emitted from the patient's body. This is different from x-ray imaging,
where x
rays pass through the body from an outside source. The areas where the
radiation is most intense would appear to be bright on the image, and in our
example this could represent the presence of cancer.
Gamma cameras contain a sheet of crystal. The atoms in the crystal absorb
the
gamma ray energy and, a fraction of a second later, emit some of that
energy in
the form of light. The electronics in the gamma camera determine the
position
of each flash of light. Those positions are sent to a computer which keeps
track of the number of flashes detected. The areas of the image which
represent
the highest number of flashes will be the brightest areas. You might find it
interesting to know that the official word for an image formed this way is
'radioscintigram'. 'Radio' refers to the radioactive substance, 'scinti'
comes
from the Latin word for 'spark', and 'gram' comes from the Greek word for
'writing'. So Nuclear Medicine imaging is literally 'writing with sparks'. I
hope this helps, Reuben. For more information, check out the web site of the
Society of Nuclear Medicine at http://www.snm.org or the European
Association of
Nuclear Medicine at http://www.eanm.org.
Best Wishes,
-JGW
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Update: June 2012
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