CT Scan of the Head
CT (computed tomography), sometimes called CAT scan, uses special x-ray equipment to obtain many images from different angles, and then join them together to show a cross-section of body tissues and organs. CT scanning provides more detailed information on head injuries, brain tumors, and other brain diseases than do regular radiographs (plain films). It also can show bone, soft tissues, and blood vessels in the same images. CT of the head and brain is a patient-friendly exam that involves little radiation exposure.
What are some common uses of the procedure?
CT can assist in:
locating skull fractures and brain damage in patients with head injuries
detecting a blood clot or bleeding within the brain shortly after a patient exhibits symptoms of a stroke
determining the extent of bone and soft tissue damage in patients with facial trauma, and planning surgical reconstruction
detecting and localizing bleeding in a patient with sudden severe headache who may have a ruptured or leaking aneurysm
detecting some brain tumors
diagnosing disease of the temporal bone on the side of the skull, which may cause hearing problems
planning radiation therapy for cancer of the brain or other tissues guiding the passage of a needle used to obtain a tissue sample (biopsy) from the brain.
How should I prepare for the procedure?
You should wear comfortable, loose-fitting clothing for your CT exam. You may be asked to remove any metallic items that might interfere with imaging of the head - such as earrings, eyeglasses, or dentures.
No special preparation is needed for a CT scan of the head unless you are to receive a contrast material - a substance that highlights the brain and its blood vessels and makes abnormalities easier to see. If the radiologist believes that an intravenous (IV) injection of a contrast material will be helpful, you will be asked in advance whether you have had allergies in the past or have ever had a serious reaction to medications. Many contrast materials contain iodine, which can cause such a reaction in persons who are allergic. The radiologist also should know if you have asthma, multiple myeloma, or any disorder of the heart, kidneys, or thyroid gland, or if you have diabetes - particularly if you are taking Glucovance or Glucophage. Typically you will be asked to sign an "informed consent" form before having CT with injection of a contrast material.
Women should always inform their doctor or x-ray technologist if there is any possibility that they are pregnant. In some cases an alternate study will be performed to reduce or eliminate the radiation exposure to the fetus.
What does the equipment look like?
The CT scanner is a large, square machine with a hole in the center, something like a doughnut. The patient lies still on a table that can move up or down, and slide into and out from the center of the hole. Within the machine, an x-ray tube on a rotating gantry moves around the patient's body to produce the images, making clicking and whirring noises as the arm moves. Though the technologist will be able to see and speak to you, you will be alone in the room during the exam.
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How does the procedure work?
Unlike conventional x-rays, which produce pictures of the "shadows" cast by body structures of different density, CT scanning uses x-rays in a much different way. In CT of the head, numerous x-ray beams are passed through the skull and brain at different angles, and special sensors measure the amount of radiation absorbed by different tissues (and lesions such as a tumor). The scanner revolves around the patient, who is lying still, emitting and recording x-ray beams from as many as a thousand points on the circle. A special computer program then uses the differences in x-ray absorption to form cross-sectional images, or "slices", of the head and brain. These slices are called tomograms, hence the name "computed tomography".
How is the procedure performed?
CT scanning may be performed in the hospital or at an outpatient radiology center, but in either case your doctor must give you a written referral. You will lie on a table that is guided into the center of the scanner, and you will be asked to lie very still.
Some patients will require an injection of a contrast material to enhance the visibility of certain tissues or blood vessels. A small needle connected to an intravenous line is placed in an arm or hand vein. Through this line, the contrast material will be injected.
Depending on the number of images needed a CT exam of the head and brain can take between 10 and 45 minutes.
What will I experience during the procedure?
When you enter the scanner, special lights may be turned on to ensure correct positioning. Some types of exams (such as a scan of the sinuses) call for a special head holder that uses soft straps to keep the head and neck in proper alignment. In all cases, the patient and technologist can talk at any time via an intercom.
CT itself causes no pain, though there may be some discomfort from the need to remain still. If contrast material is injected you may have a warm, flushed sensation during the injection. You may also experience a metallic taste in your mouth that lasts for one or two minutes. Occasionally a patient will develop itching and hives for up to a few hours after the injection, which can be relieved with medication. Because CT uses x-rays, you may not have a relative or friend in the CT room during the exam.
Who interprets the results and how do I get them?
A radiologist, a physician experienced in CT and other radiology examinations, will analyze the images and send a signed report with his or her interpretation to the patient's personal physician. The personal physician's office will inform the patient on how to obtain their results.