What is 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
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,
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
How are nuclear medicine scans done?
As stated above, nuclear medicine scans may be performed on many organs and tissues
of the body. Each type of scan employs certain technology, radionuclides, and procedures.
A nuclear medicine scan consists of 3 phases: tracer (radionuclide) administration,
taking images, and image interpretation. The amount of time between administration
of the tracer and the taking of the images may range from a few moments to a few days.
The time depends on the body tissue being examined and the tracer being used. Some
scans are completed in minutes, while others may need the patient to return a few
times over the course of several days.
One of the most commonly performed nuclear medicine exams is a heart scan. Myocardial
perfusion scans and radionuclide angiography scans are the 2 primary heart scans.
In order to give an example of how nuclear medicine scans are done, the process for
a resting radionuclide angiogram (RNA) scan is presented below.
Although each facility may have specific protocols in place, generally, a resting
RNA follows this process:
The patient will be asked to remove any jewelry or other objects that may interfere
with the procedure.
If the patient is asked to remove clothing, he or she will be given a gown to wear.
An intravenous (IV) line will be started in the hand or arm.
The patient will be connected to an electrocardiogram (ECG) machine with electrodes
(leads) and a blood pressure cuff will be attached to the arm.
The patient will lie flat on a table in the procedure room.
The radionuclide will be injected into the vein to "tag" the red blood cells. Alternatively,
a small amount of blood will be withdrawn from the vein so that it can be tagged with
the radionuclide. The radionuclide will be added to the blood and will be absorbed
into the red blood cells.
After the tagging procedure, the blood will be returned into the vein through the
IV tube. The progress of the tagged red blood cells through the heart will be traced
with a scanner.
During the procedure, it will be very important to lie as still as possible. Any movement
can adversely affect the quality of the scan.
The gamma camera will be positioned over the patient as he or she lies on the table,
and will obtain images of the heart as it pumps the blood through the body.
The patient may be asked to change positions during the test. However, once the position
has been changed, the patient will need to lie still without talking.
After the scan is complete, the IV line will be discontinued. The patient will be
allowed to leave, unless the healthcare provider gives different instructions.