Diagnostic Nuclear Medicine Examinations: Radioisotope Scintillation
Scanning (Scintiscan)
In nuclear medicine, radioactive substances known as radioisotopes
are administered to the patient in order to diagnose disease. A
radioactive isotope
disintegrates spontaneously (ultimately losing its radioactivity)
and emits gamma rays from within the body which enable the physician
to visualize internal abnormalities. This differs from x-ray procedures
where the x-rays are passed through the body from an external source.
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Examples of radioactive isotopes, commonly
used for isotope-imaging studies, are gallium, iodine, and
technetium. Sometimes non-radioactive compounds are simply
labeled or tagged with a radioactive isotope and sometimes
radioactive tracers (radioactive pharmaceuticals) are given
by mouth or by vein. Some of the isotopes are selectively
absorbed by tumors or by specific organs in the body. The
concentrated radioisotopes outline the tumor or organ making
it visible
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on the photoscanner by the emission of the radioactive energy. Much
research in nuclear medicine is concerned with attempts to find new
radioisotopes and to develop radioisotope-labeled compounds that will
be selectively absorbed in specific parts of the body.
A device called a photoscanner is used to measure the radioactivity
from the nuclear substance absorbed by various parts of the body.
A two dimensional representation or map can be made of the rays
emitted from the radioisotope which shows where it is concentrated
in the body tissue. Findings of such an examination are photographically
recorded and are referred to as scans. The more common scans are
illustrated in the diagram on the next page (Diagnostic Imaging
-- Nuclear Medicine), -- bone, kidney, thyroid, brain, salivary
glands, heart/lung, liver/spleen, and total body. Bone scanning
with various bone-seeking isotopes is advocated for earlier diagnosis
of bone metastasis. Other names for these types of scans are scintiscan,
gallium scan, and lymphoscintography.
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