Nuclear Medicine
Nuclear medicine is a specialized area of radiology that
uses very small amounts of radioactive materials, or radiopharmaceuticals, to
examine organ function and structure. Nuclear medicine imaging is a combination
of many different disciplines. These include chemistry, physics, mathematics,
computer technology, and medicine. This branch of radiology is often used to
help diagnose and treat abnormalities very early in the progression of a
disease, such as thyroid cancer.
Because X-rays pass through soft tissue, such as intestines,
muscles, and blood vessels, these tissues are difficult to visualize on a
standard X-ray, unless a contrast agent is used. This allows the tissue to be
seen more clearly. Nuclear imaging enables visualization of organ and tissue structure
as well as function. The extent to which a radiopharmaceutical is absorbed, or
"taken up," by a particular organ or tissue may indicate the level of
function of the organ or tissue being studied. Thus, diagnostic X-rays are used
primarily to study anatomy. Nuclear imaging is used to study organ and tissue
function.
A tiny amount of a radioactive substance is used during the
procedure to assist in the exam. The radioactive substance, called a
radionuclide (radiopharmaceutical or radioactive tracer), is absorbed by body
tissue. Several different types of radionuclides are available. These include
forms of the elements technetium, thallium, gallium, iodine, and xenon. The
type of radionuclide used will depend on the type of study and the body part
being studied.
After the radionuclide has been given and has collected in
the body tissue under study, radiation will be given off. This radiation is
detected by a radiation detector. The most common type of detector is the gamma
camera. Digital signals are produced and stored by a computer when the gamma
camera detects the radiation.
By measuring the behavior of the radionuclide in the body
during a nuclear scan, the healthcare provider can assess and diagnose various
conditions, such as tumors, infections, hematomas, organ enlargement, or cysts.
A nuclear scan may also be used to assess organ function and blood circulation.
The areas where the radionuclide collects in greater amounts
are called "hot spots." The areas that do not absorb the radionuclide
and appear less bright on the scan image are referred to as "cold
spots."
In planar imaging, the gamma camera remains stationary. The
resulting images are two-dimensional (2D). Single photon emission computed
tomography, or SPECT, produces axial "slices" of the organ in
question because the gamma camera rotates around the patient. These slices are
similar to those performed by a CT scan. In certain instances, such as PET
scans, three-dimensional (3D) images can be performed using the SPECT
data.
Scans are used to diagnose many medical conditions and
diseases. Some of the more common tests include the following:
Renal scans. These are used to examine the kidneys and
to find any abnormalities. These include abnormal function or obstruction of
the renal blood flow.
Thyroid scans. These are used to evaluate thyroid
function or to better evaluate a thyroid nodule or mass.
Bone scans. These are used to evaluate any
degenerative and/or arthritic changes in the joints, to find bone diseases and
tumors, and/or to determine the cause of bone pain or inflammation.
Gallium scans. These are used to diagnose active
infectious and/or inflammatory diseases, tumors, and abscesses.
Heart scans. These are used to identify abnormal blood
flow to the heart, to determine the extent of the damage of the heart muscle
after a heart attack, and/or to measure heart function.
Brain scans. These are used to investigate problems
within the brain and/or in the blood circulation to the brain.
Breast scans. These are often used in conjunction with
mammograms to locate cancerous tissue in the breast.
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