|
CT contrast agents, sometimes
referred to as "dyes," are used to highlight specific areas so that
the organs, blood vessels, or tissues are more visible. By
increasing the visibility of all surfaces of the organ or tissue
being studied, they can help the radiologist determine the presence
and extent of disease or injury.
Contrast agents are available in several different forms, but in
general a CT contrast agent is a pharmaceutical substance. Some of
the more common contrast agents used are:
- Iodine
- Barium
- Barium sulfate
- Gastrografin
Contrast agents for CT examinations are administered in four
different ways:
- Intravenous injection
- Oral administration
- Rectal administration
- Inhalation-this is a relatively uncommon procedure in which
xenon gas is inhaled for a highly specialized form of lung or
brain imaging. The technique, xenon CT, is only available at a
small number of locations worldwide and is used only for rare
cases.
Intravenous
Contrast
Intravenous contrast is used to highlight blood vessels and to
enhance the structure of organs like the brain, spine, liver, and
kidney. The contrast agent (usually an iodine compound) is clear,
with a water-like consistency. Typically the contrast is contained
in a special injector, which injects the contrast through a small
needle taped in place (usually on the back of the hand) during a
specific period in the CT exam.
Once the contrast is injected into the bloodstream, it circulates
throughout the body. The CT's x-ray beam is weakened as it passes
through the blood vessels and organs that have "taken up" the
contrast. These structures are enhanced by this process and show up
as white areas on the CT images. When the test is finished, the
kidneys and liver quickly eliminate the contrast from the body.
|
Need To Know:
Is Iodine a Safe Contrast Agent?
Iodine is considered to be a safe contrast agent. It has been
used for many years without serious side effects. Because iodine
contrast increases the visibility of target tissues on the
images, the benefits are considered to outweigh the risks.
The most common side effect of iodine is a warm or "flushed"
sensation during the actual injection of the iodine, followed
sometimes by a metallic taste in the mouth that usually lasts
for less than a minute. No treatment is necessary for this
sensation, if experienced.
Another mild reaction is itching over various parts of the
body. This reaction lasts from several minutes to a few hours
after the injection. When this reaction occurs, medication is
usually administered to counteract the itching.
More serious allergic reactions, while uncommon, include
difficulty breathing and swelling of the throat or other parts
of the body. These reactions, if experienced, are treated
immediately.
Newer forms of contrast help to reduce the risk of an
allergic reaction. If you have had an allergic reaction to
iodine or a contrast agent in the past, the physician may
recommend on of these newer agents.
In some cases, CT can still provide valuable diagnostic
information without the administration of a contrast agent, so
the physician may decide this is the best course of action. |
Oral CT Contrast
Oral contrast is used to highlight gastrointestinal (GI) organs
in the abdomen and pelvis. If oral contrast will be used during an
examination, the patient will be asked to fast for several hours
before administration.
Two types of oral contrast are used:
Barium sulfate, the most common oral contrast agent, resembles a
milk shake in appearance and consistency. The compound, available in
various flavors, is prepared by mixing with water.
Gastrografin is a yellowish, water-based drink mixed with iodine.
It can have a bitter taste.
When oral contrast has been requested by the doctor, patients
usually drink about 1,000 cc to 1,500 cc (the equivalent of three or
four 12-ounce drinks).
After the contrast is swallowed, it travels to the stomach and
gastrointestinal tract. Like intravenous iodine, barium and
gastrografin weaken x-rays. On CT images, the organs that have
"taken up" the contrast appear as highlighted white areas.
|
Need To Know:
Is Oral Contrast Safe?
In general, both barium and gastrografin contrast are safe
and pass uneventfully through the gastrointestinal tract. Minor
and temporary side effects, such as constipation, may occur. |
Rectal CT Contrast
Rectal
contrast is used when enhanced images of the large intestine and
other lower GI organs are required. The same types of contrast used
for oral contrast are used for rectal contrast, but in different
concentrations.
Rectal CT contrast is usually administered by enema. When the
contrast is administered, the patient may experience mild
discomfort, coolness, and a sense of fullness. After the CT is
complete, the contrast is drained and the patient may go to the
bathroom.
The preparation for rectal contrast is similar to oral contrast,
in that the patient should be fasting for several hours before the
test. In addition, the patient will be required to use a Fleets
Enema to cleanse the colon; it is usually used the night before the
examination.
|
Need To Know:
Is Rectal Contrast Safe?
Rectal contrast is considered to be safe and passes through
the gastrointestinal tract uneventfully. Minor and temporary
side effects, such as constipation, can occur. |
Administration of
Contrast media and breast feading
|
