CT scanning—sometimes called CAT scanning—is a noninvasive,
painless medical test that helps physicians diagnose
and treat medical conditions.
CT imaging uses special x-ray equipment to produce multiple
images or pictures of the inside of the body and a computer
to join them together in cross-sectional views of the
area being studied. The images can then be examined on
a computer monitor or printed.
CT scans of internal organs, bone, soft tissue and blood
vessels provide greater clarity than conventional x-ray
exams.
This procedure is typically used to help diagnose the
cause of abdominal pain and diseases of the bowel and
colon, such as:
- abscesses in the abdomen
- inflamed colon
- cancers of the colon, liver, pancreas and kidneys
- pancreatitis
- lymphoma
- staging for cancer
- diverticulitis
- appendicitis
CT scanning of the abdomen/pelvis is also performed
to:
- visualize the liver, spleen, pancreas and kidneys
- plan and properly administer radiation treatments
for tumors
- guide biopsies and other minimally invasive procedures
CT imaging can also play a significant role in the detection,
diagnosis and treatment of vascular disorders that can
lead to stroke, gangrene or kidney failure.
You should wear comfortable, loose-fitting clothing
to your exam. You may be given a gown to wear during
the procedure.
Metal objects including jewelry, eyeglasses, dentures
and hairpins may affect the CT images and should be left
at home or removed prior to your exam. You may also be
asked to remove hearing aids and removable dental work.
You may be asked not to eat or drink anything for several
hours beforehand, especially if a contrast material will
be used in your exam. You should inform your physician
of any medications you are taking and if you have any
allergies, especially to contrast materials.
Also inform your doctor of any recent illnesses or other
medical conditions, and if you have a history of heart
disease, asthma, diabetes, kidney disease or thyroid
problems. Any of these conditions may increase the risk
of an unusual adverse effect.
Women should always inform their physician or technologist
if there is any possibility that they are pregnant.
The CT scanner is typically a large machine with a hole,
or tunnel, in the center. A moveable examination table
slides into and out of this tunnel. In the center of
the machine, the x-ray tube and electronic x-ray detectors
are located opposite each other on a ring, called a gantry,
which rotates around you. The computer that processes
the imaging information and monitor are located in a
separate room.
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.
For some CT exams, a contrast material is used to enhance
visibility in the area of the body being studied.
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 swallowed,
injected through an intravenous line (IV) or administered
by enema, depending on the type of examination.
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 CT scanning is usually completed within 30 minutes.
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.
Many patients also receive iodine intravenously (injected
into a vein) to help evaluate blood vessels and organs
such as the liver, kidneys and pancreas.
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.
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.
Benefits
- Viewing a CT scan, an experienced radiologist can
diagnose many causes of abdominal pain with very high
accuracy, enabling faster treatment and often eliminating
the need for additional, more invasive diagnostic procedures.
- When pain is caused by infection and inflammation,
the speed, ease and accuracy of a CT examination can
reduce the risk of serious complications caused by
a burst appendix or ruptured diverticulum and the subsequent
spread of infection.
- 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 10 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.
A person who is very obese may not fit into the opening
of a conventional CT unit.
CT Scanning of the abdomen may not be as sensitive in
identifying gallstones as ultrasound of the abdomen.
For some conditions, including but not limited to some
liver, adrenal and pancreatic abnormalities, the evaluation
and diagnosis with MRI may be preferable over CT scanning.
Reference:
http://www.radiologyinfo.org/
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Diagnostics 
