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Welcome, eCureMe.com medical contents search April 26, 2013
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Brain Computed Tomography




Brain CT, brain CT scan, brain CAT (computerized axial tomography) scan




  • Computed tomography (or computerized axial tomography) is an examination that uses X-ray to obtain a cross-sectional image of the human body.
  • When X-rays are irradiated on the human body, some of the rays are absorbed and some pass through the body to produce an image. In plain X-ray imaging, the film directly absorbs penetrated X-rays. In CAT scanning, an electronic device called a "detector array" absorbs the penetrated X-rays, measures the X-ray amount, and transmits the data to a computer system. A sophisticated computer system, in turn, calculates and analyzes data from each detector in each level, and finally reconstructs multiple, two-dimensional, cross-sectional images. An X-ray source and a CAT scan detector rotate around the patient to obtain each cross-sectional image.
  • CT scan images represent the density and atomic number of human tissue just like general X-ray imaging, such as chest and bone X-rays. The denser the tissue, and the higher the atomic number, the whiter the CAT image is. Bone and calcium appear white; air in the lungs appears black; water, blood, and internal organs such as liver, kidneys, and intestines appear gray; and fat tissue appears dark gray.




  • Provides detailed, two-dimensional images with great clarity. This method provides higher quality images of many types of tissue, including those of the lungs, bones, soft tissue, and blood vessels.
  • Fast. In case of trauma, CAT scan can reveal internal bleeding and other life-threatening injuries quickly.
  • Simple, painless, and non-invasive
  • Sensitive in detecting traumatic injuries, cancer, and many other diseases
  • Cost-effective imaging tool for a wide range of clinical problems (when compared to MRI)
  • It can distinguish normal from abnormal structures accurately. It is useful in guiding biopsies, in fluid removal/aspiration, in drainage of abscesses, and in other minimally invasive procedures and radiotherapy.
  • It can make three-dimensional images.




  • Head injury -- to detect skull fractures, brain damage, facial bones and soft tissue damage
  • Stroke -- to detect bleeding, blood clots within the brain
  • When ruptured aneurysm is suspected
  • To detect and evaluate tumors of the brain and skull
  • Planning radiation therapy




  • Stroke
  • Brain/skull injury: concussion, contusion, epidural hematoma, subdural hematoma, subarachnoid hemorrhage
  • Aneurysm
  • Vascular anomalies/related hemorrhage
  • Tumor/cancer of brain, skull, meninges
  • Congenital anomalies/birth defects
  • Hydrocephalus
  • Neurological diseases
  • Infection (herpes, tuberculosis, fungus, etc.), abscesses
  • Inflammation
  • Metastasis




  • You will be asked to lie down on the CAT table.
  • Pillows will support your head.
  • After the proper positioning, the technologist will go into a console room, and start exposing X-rays into your body.
  • Once the X-ray tube rotates around your head 360 degrees to take one cross-sectional image, the table will move a little bit to get the next slice.
  • You will be alone in the examining room during X-ray exposure, but you can talk and listen to your technologist using an intercom, or simply communicate with your hands as needed. The technologist will be watching you during the scanning through a glass window and video camera.
  • In the event a contrast medium is needed to make the organs and blood vessels stand out, it will be injected into your vein during the exam.
  • The exam usually takes from ten minutes to half an hour.




  • You will be asked to remove jewelry, eyeglasses, dentures, hairpins, hearing aids, etc.
  • For contrast enhanced CAT scanning, you should not eat or drink for one or more hours before the exam. A contrast agent will be injected into your blood stream a moment before scanning. If you have had any allergic reactions to the contrast medium, certain medications, iodine, and foods, or if you have a history of kidney problems, asthma, thyroid problems, diabetes, or a heart condition, you will be asked to inform your technologist or doctor.
  • Lie still on the examining table until the technologist asks you to get down.
  • If you are pregnant or suspect pregnancy, you should inform your doctor,




  • A radiologist (a physician specialist trained to interpret CAT images or other radiology exams, such as X-ray, MRI, mammography, etc.) reviews the CAT scan and reports the results to your personal doctor.
  • The physician's office informs patients when the results are in, and what the results are. The office uses the results as a reference in evaluating and treating patients.




  • Radiation exposure. Radiation exposure during a CAT examination is equal to a year's worth of natural background radiation (i.e., from radon gas in our homes, soil, or from cosmic rays.) It is much more than the radiation exposure from general X-ray studies, such as chest and skull X-rays, but it is less than that from a barium enema, an upper GI series, or cardiac catheterization. The benefits of CT study outweigh the risk of radiation exposure. But in the case of children, special care should be taken to expose them to only necessary amounts of radiation, because growing children are more sensitive to radiation hazard.
  • Adverse reactions to contrast agents given intravenously:
    1. Allergic reactions such as rash, hives, itching. Usually self-limiting; antihistamine can be given.
    2. Anaphylactic reaction -- causing difficulty breathing, swelling in the throat, or other parts of the body -- is potentially life threatening. It is treated with epinephrine, corticosteroids, and antihistamine. It is very rare. Radiology departments are well trained to deal with anaphylactic reactions.
    3. Kidney failure, especially if the patient is taking Glucophage (metformin) for diabetes.
  • Nursing mothers cannot start breast-feeding for 24 hours after receiving the contrast medium intravenously.




  • Bone, air, fat, and other tissue are easily distinguished with CAT scanning because they appear distinctly due to different densities. But it is difficult to distinguish body organs, tumor, cancer, blood vessels, muscle, and fluid from one another. Injection of a contrast medium can increase the capability of differentiating soft tissue. Sometimes MRI can be a better imaging method for evaluating soft tissue.
  • CAT scans only provide axial cross-sections. When the longitudinal cross- sections are needed to evaluate a problem, such as the extent of prostate cancer growth or cervix cancer spread, CAT scan can play only a limited role. MRI may be needed instead.









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