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 tumours, 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.
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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 tumour, 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 tumour.
- 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), such as 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.
- Take metformin. You may have to adjust your medicine for a day before and after the test.
- Have had kidney problems.
- Have asthma.
- 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 .
How It Is Done
You may need to take off any jewellery, 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.
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 breastfeed and are concerned about whether the dye used in this test is safe, talk to your doctor. Most experts believe that very little dye passes into breast milk and even less is passed on to the baby. But if you prefer, you can store some of your breast milk ahead of time and use it for a day or two after the test.
- 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 getting cancer from having some types of CT scans.footnote 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.
Complete results usually are ready for your doctor in 1 to 2 days.
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.
A growth, such as a tumour, 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 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. To learn more, 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. To learn more, see the topic Magnetic Resonance Imaging (MRI).
- 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.
- Pearce MS, et al. (2012). Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: A retrospective cohort study. Lancet, 380(9840): 499–505.
- 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/MedicalDevices/Safety/AlertsandNotices/PublicHealthNotifications/ucm061994.htm.
Current as of: December 9, 2019
Author: Healthwise Staff
Medical Review: Adam Husney, MD - Family Medicine
Brian O'Brien, MD, FRCPC - Internal Medicine
E. Gregory Thompson, MD - Internal Medicine
Martin J. Gabica, MD - Family Medicine
Howard B. Schaff, MD - Diagnostic Radiology
Current as of: December 9, 2019