Test Overview
A computed tomography (CT) scan uses
X-rays to make pictures of the head and face.
During the test, you will lie on a table that is attached to the CT
scanner, which is a large doughnut-shaped machine. Your head will be positioned
inside the scanner. The CT scanner sends X-rays through the head. Each rotation
of the scanner provides a picture of a thin slice of the
head and face. One part of the scanning machine can tilt to take pictures from
different positions. All of the pictures are saved as a group on a computer.
They also can be printed.
In some cases, a
dye called contrast material may be put in a vein (IV) in your arm or into the spinal canal. The dye makes structures and organs easier to see on the CT
pictures. The dye may be used to check blood flow and look for
tumors, areas of
inflammation, or nerve damage.
A
CT scan of the head can give some information about the eyes, facial bones,
air-filled cavities (sinuses) within the bones around the nose, and the inner
ear. If these areas are of concern, a specific CT scan of the area is usually
done.
A CT scan of the head may be used to evaluate headaches. For
more information, see:
Headaches: Should I Have Imaging Tests to Find Out What's Causing My Headaches?
Why It Is Done
A CT scan of the head is done
to:
- Find the cause of symptoms, such as confusion,
paralysis, numbness, vision problems,
vertigo, or headaches, that might mean a brain injury,
a brain tumor, a ruptured
aneurysm, or bleeding inside the
head.
- Look for problems of the middle ear bones and the
auditory nerve.
- Help plan for surgery.
- Find damage caused by a
stroke and to help find the best treatment for the
cause of a stroke.
- Find the cause of a loss of consciousness or a
changing level of consciousness.
- Check on the success of treatment
or surgery for a brain tumor.
- Provide guidance for a brain
biopsy.
CT scans of the eyes, facial area, and sinuses may be done
to:
- Look for problems of the eyes and the
optic nerve. The test may find fractures of the bones
around the eyes or foreign objects in the eye.
- Look for problems or
diseases of the air-filled cavities in the bones around the nose (sinuses).
- Look for problems with the bones
and joints of the jaw, face, and skull, such as
temporomandibular disorder or
Paget's disease.
- Find broken bones (fractures). See a
CT scan of a cheekbone fracture.
- Look for foreign objects in the head
and face.
- Plan for surgery to rebuild parts of the face that were
damaged.
How To Prepare
Before the CT scan, tell your doctor
if you:
- Are or might be pregnant.
- Are allergic to any medicines, including iodine
dyes.
- Have a heart condition, such as
heart failure.
- Have
diabetes or take metformin (Glucophage) for your
diabetes. You may have to adjust your medicine for a day before and
after the test.
- Have had kidney
problems.
- Have
asthma.
- Have a medical device, such as a pacemaker or an
insulin pump.
- Have had
multiple myeloma.
- Become very nervous in
small spaces. You need to lie still inside the CT scanner, so you may need a
medicine (sedative) to help you relax.
Arrange for someone to take you home in case you get a
medicine to help you relax (sedative) for the test.
Talk to your
doctor about any concerns you have regarding the need for
the test, its risks, or how it will be done. To help you understand the
importance of this test, fill out the
medical test information form(What is a PDF document?).
How It Is Done
A CT scan is usually done by a
radiology technologist. The pictures are usually read
by a
radiologist, who writes the report. Other doctors also may review a CT scan.
You
may need to take off any jewelry, glasses, and hearing aids. Wear comfortable,
loose-fitting clothes.
During the test, you will lie on a table
that is attached to the CT scanner.
Straps will hold your head still but your face will not be covered.
The table slides into the round opening of the scanner, and the scanner
moves around your body. The table will move while the scanner takes pictures.
You may hear a click or buzz as the table and scanner move. It is very
important to lie still during the test.
During the test, you may
be alone in the scan room. But the technologist will watch you through a
window. You will be able to talk to the technologist through a two-way
intercom.
The test will take about 30 to 60 minutes. Most of this time is spent getting ready for the scan. The actual scan only takes a few seconds.
How It Feels
The test will not cause pain.
The table you lie on may feel hard, and the room may be cool. It may be hard to
lie still during the test.
Some people feel nervous inside the CT
scanner.
If a medicine to help you relax (sedative) or
dye (contrast material) is used, an IV is usually put in
your hand or arm. You may feel a quick sting or pinch when the IV is started.
The dye may make you feel warm and flushed and give you a metallic taste in
your mouth. Some people feel sick to their stomach or get a headache. Tell the
technologist or your doctor how you are feeling.
Risks
The chance of a CT scan causing a problem is
small.
- There is a chance of an
allergic reaction to the dye (contrast material).
- If you have
diabetes or take metformin (Glucophage), the dye may
cause problems. Your doctor will tell you when to stop taking metformin and
when to start taking it again after the test so you will not have
problems.
- There is a small chance of developing cancer from having
some types of CT scans.1 The chance is higher in children, young
adults, and people who have many radiation tests. If you are
concerned about this risk, talk to your doctor about the amount of radiation
this test may give you or your child and confirm that the test is
needed.
- There is a slight risk that the CT scan can interfere
with implanted or external medical devices. Examples of medical devices include
pacemakers, insulin pumps, defibrillators, and
neurostimulators.
Results
A computed tomography (CT) scan uses
X-rays to make detailed pictures of the head and
face.
The radiologist may discuss the
CT scan with you right after the test. But
complete results usually are ready for your doctor in 1 to 2 days.
CT scan of the head and face| Normal: | The brain and blood vessels
and bones of the skull and face are normal in size, shape, and
position. |
|---|
No foreign objects or growths
are present. |
No bleeding or collections of
fluid are present. |
|
Abnormal: | A growth, such as a tumor, or
bleeding is present in or around the brain. Foreign objects, such as glass or
metal fragments, are present. The bones of the skull or face are broken
(fractured) or look abnormal. Nerves leading to or from the brain are damaged
or pinched. |
|---|
A collection of fluid is
found, which may mean bleeding in or around the brain. |
An
aneurysm is present. |
The openings in the brain
(ventricles) through which
cerebrospinal fluid flows into the spine are enlarged.
An area of the brain shows swelling (edema) or other
changes that may mean a
stroke. |
The
sinuses are filled with fluid or have a thick
lining. |
What Affects the Test
The following may stop you from
having the test or may change the test results:
- Pregnancy. CT scans are not usually done during
pregnancy.
- Metal objects in the head.
These items, such as surgical clips, aneurysm clips, or foreign bodies, may prevent
a clear view of the body area.
- You are not able to lie still during the test.
What To Think About
- Sometimes your CT test results may be different
than those from other types of X-ray tests,
magnetic resonance imaging (MRI), or
ultrasound scans because the CT scan provides a
different view.
- Children who need a CT scan may need special
instructions for the test. If the child is too young to hold still or is
afraid, the doctor may give the child a medicine (sedative) to
help him or her relax.
- If your child is scheduled for a CT scan,
talk with your child's doctor about the need for the scan and the risk of
radiation exposure to your child.
- Special
CT scanners called spiral (helical) CT scanners and multi-slice (or
multi-detector) CT scanners are sometimes used for this test. They can find
aneurysms or
atherosclerosis. These special CT scanners can:
- Take better pictures of blood vessels and
organs.
- Produce scans in less time.
- Perfusion CT is a method to look at blood flow
in the brain. For this test, a dye (contrast material) is given intravenously (IV), and CT scans then follow the flow
of the dye through the brain. This type of CT scan can show damaged areas of
the brain. The scans also can show areas of the brain that are not getting any
blood flow.
- CT results are often compared to positron emission
tomography (PET) results to help find cancer. Some new scanners do both scans
at the same time.
- A
CT angiogram can show two- and three-dimensional
pictures of blood vessels. For more information, see the topic
Angiogram of the Head and Neck.
- MRI may
give additional information after a CT scan of the head and face is done.
For more information, see
the topic
Magnetic Resonance Imaging (MRI).
References
Citations
- Einstein AJ, et al. (2007). Estimating risk of cancer
associated with radiation exposure from 64-slice computed tomography coronary
angiography. JAMA, 298(3): 317–323.
Other Works Consulted
- Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
- U.S. Food and Drug Administration (2008).
FDA preliminary public health notification: Possible malfunction of electronic
medical devices caused by computed tomography (CT) scanning. Available online:
http://www.fda.gov/cdrh/safety/071408-ctscanning.html.
Credits
| By | Healthwise Staff |
|---|
| Primary Medical Reviewer | Adam Husney, MD, MD - Family Medicine |
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| Specialist Medical Reviewer | Howard Schaff, MD - Diagnostic Radiology |
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| Last Revised | June 13, 2011 |
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