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Diagnostics | top |  |
How does the procedure work?
In many ways CT scanning works very much like other
x-ray examinations. X-rays are a form of radiation—like
light or radio waves—that can be directed at the body.
Different body parts absorb the x-rays in varying degrees.
In a conventional x-ray exam, a small burst of radiation
is aimed at and passes through the body, recording an
image on photographic film or a special image recording
plate. Bones appear white on the x-ray; soft tissue shows
up in shades of gray and air appears black.
With CT scanning, numerous x-ray beams and a set of electronic
x-ray detectors rotate around you, measuring the amount
of radiation being absorbed throughout your body. At
the same time, the examination table is moving through
the scanner, so that the x-ray beam follows a spiral
path. A special computer program processes this series
of pictures, or slices of your body, to create two-dimensional
cross-sectional images, which are then displayed on a
monitor.
CT imaging is sometimes compared to looking into a loaf
of bread by cutting the loaf into thin slices. When the
image slices are reassembled by computer software, the
result is a very detailed multidimensional view of the
body's interior.
Refinements in detector technology allow new CT scanners
to obtain multiple slices in a single rotation. These
scanners, called "multislice CT" or "multidetector
CT," allow thinner slices to be obtained in a shorter
period of time, resulting in more detail and additional
view capability.
Modern CT scanners are so fast that they can scan through
large sections of the body in just a few seconds. Such
speed is beneficial for all patients but especially children,
the elderly and critically ill.
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How is the CAT scan performed?
The technologist begins by positioning you on the CT
examination table, usually lying flat on your back or
possibly on your side or on your stomach. Straps and
pillows may be used to help you maintain the correct
position and to hold still during the exam.
If a contrast material is used, it will be injected into
a vein shortly before scanning begins.
Next, the table will move quickly through the scanner
to determine the correct starting position for the scans.
Then, the table will move slowly through the machine
as the actual CT scanning is performed.
You may be asked to hold your breath during the scanning.
When the examination is completed, you will be asked
to wait until the technologist determines that the images
are of high enough quality for the radiologist to read.
The actual CT scanning takes less than 30 seconds and
the entire process is usually completed within 30 minutes.
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What will I experience during the procedure?
Most CT exams are painless, fast and easy. With spiral
CT, the amount of time that the patient needs to lie
still is reduced.
Though the scanning itself causes no pain, there may
be some discomfort from having to remain still for several
minutes. If you have a hard time staying still, are claustrophobic
or have chronic pain, you may find a CT exam to be stressful.
The technologist or nurse may offer you a mild sedative
to help.
If an intravenous contrast material is used, you will
feel a slight pin prick when the needle is inserted into
your vein. You may have a warm, flushed sensation during
the injection of the contrast materials and a metallic
taste in your mouth that lasts for a few minutes. Occasionally,
a patient will develop itching and hives, which can be
relieved with medication. If you become light-headed
or experience difficulty breathing, you should notify
the technologist or nurse, as it may indicate a more
severe allergic reaction.
If the contrast material is swallowed, you may find the
taste mildly unpleasant; however, most patients can easily
tolerate it. You can expect to experience a sense of
abdominal fullness and an increasing need to expel the
liquid if your contrast material is given by enema. In
this case, be patient, as the mild discomfort will not
last long.
When you enter the CT scanner, special lights may be used to ensure that you are properly positioned. With modern CT scanners, you will hear only slight buzzing, clicking and whirring sounds as the CT scanner revolves around you during the imaging process.
You will be alone in the exam room during the CT scan,
however, the technologist will be able to see, hear and
speak with you at all times.
With pediatric patients, a parent may be allowed in the
room but will be required to wear a lead apron to prevent
radiation exposure.
After a CT exam, you can return to your normal activities.
If you received a contrast material, you may be given
special instructions.
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Who interprets the results and how do I get them?
A radiologist, a physician specifically trained to supervise and interpret radiology examinations, will analyze the images and send a signed report to your primary care or referring physician, who will share the results with you.
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What are the benefits vs. risks?
Benefits
- CT is fast. This is especially important for patients with chest injury, because internal damage or bleeding can be diagnosed in time to give life-saving treatment.
- CT scanning is painless, noninvasive and accurate.
- A major advantage of CT is that it is able to image bone, soft tissue and blood vessels all at the same time.
- Unlike conventional x-rays, CT scanning provides very detailed images of many types of tissue as well as the lungs, bones, and blood vessels.
- CT examinations are fast and simple; in emergency cases, they can reveal internal injuries and bleeding quickly enough to help save lives.
- CT has been shown to be a cost-effective imaging tool for a wide range of clinical problems.
- CT may be less expensive than MRI. In addition, it is less sensitive to patient movement.
- CT can be performed if you have an implanted medical device of any kind, unlike MRI.
- CT imaging provides real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies and needle aspirations of many areas of the body, particularly the lungs, abdomen, pelvis and bones.
- A diagnosis determined by CT scanning may eliminate the need for exploratory surgery and surgical biopsy.
- No radiation remains in a patient's body after a CT examination.
- X-rays used in CT scans usually have no side effects.
Risks
- There is always a slight chance of cancer from radiation. However, the benefit of an accurate diagnosis far outweighs the risk.
- The effective radiation dose from this procedure is about 8 mSv, which is about the same as the average person receives from background radiation in three years.
- Women should always inform their physician or x-ray technologist if there is any possibility that they are pregnant.
- CT scanning is, in general, not recommended for pregnant women because of potential risk to the baby.
- Nursing mothers should wait for 24 hours after contrast material injection before resuming breast-feeding.
- The risk of serious allergic reaction to contrast materials that contain iodine is rare, and radiology departments are well-equipped to deal with them.
- Children should have a CT study only if it is essential for making a diagnosis and should not have repeated CT studies unless absolutely necessary.
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What are the limitations of CT Scanning of the Chest?
A person who is very obese may not fit into the opening
of a conventional CT unit.
Magnetic resonance imaging (MRI) may be better than CT
for showing very fine soft-tissue detail.
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Reference:
http://www.radiologyinfo.org/
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