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The Different Tests

CT Scan or CAT Scan (Computerized Axial Tomography Scan)

    The CT Scan, or CAT Scan has been in use since 1973. It takes x-rays of the brain and then combines them to form a 3 dimensional picture on the computer.  In doing this, it can examine thin sections of the brain at different depths and therefore show much greater detail than a regular x-ray.

    The CT Scan is useful for testing for a variety of damage.  It shows if there is bleeding in the skull, tumors, hemorrhages, fluid collection, and can also determine the amount of swelling.  In depressed fractures, the CT Scan has the advantage of showing the amount of depression more clearly than the regular skull x-ray.

    Some advantage of the CT Scan over other tests include such factors as it is painless, it can be performed much faster than many other tests, and it can be repeated with little risk to the patient (that is, repeated changes can be monitored).  One major disadvantage, however, is that the CT Scan sometimes shows normal in patients who have seizures.

PET Scan (Positron Emission Tomography)

    A PET scan differs from a CT scan in that while a CT scan is limited to distinguishing anatomical features, a PET scan measures metabolic processes, thus allowing an appraisal of how the brain is functioning.

     It tracks natural compounds, such as glucose, as the brain metabolizes them.  By showing the areas of different metabolic activity, it then makes it easier to make diagnoses, such as determining the areas responsible for epileptic seizures.

EEG (Electroencephalograph)

    The EEG is a recording of the electrical activity of the brain.  Its computerized printout looks similar to that of an EKG which monitors the heart. Brain activity is represented by a graph which shows peaks and valleys which lessen with decreasing levels of consciousness.

     An EEG is given by attaching small electrodes (flat pieces of plastic with wires attached to them) to the scalp.  The wires running from the electrodes are connected to a computer which then interprets the signals it is receiving and produces a print-out of the electrical activity.  EEGs are often given to patients who have seizures.  They are very useful in locating the areas of the brain where there is abnormal electrical activity.

MRI (Magnetic Resonance Imaging)

    The MRI is similar to the CT Scan; however, it uses magnetic fields instead of x-rays to produce a three-dimensional picture of brain tissue.  The MRI is useful for minor brain injuries in that it shows very small changes in the brain which may not be detected by a CT Scan or an x-ray.


    The patient is placed underneath the X-ray machine and a special photographic plate which is sensitive to X-rays is placed under the patient.  The X-ray photograph is then taken.  X-rays pass through the flesh and are absorbed by the bone.  An image of the bone is therefore left on the photographic plate and is extremely useful for diagnosing the extent of an injury.  X-rays are used to identify the presence and the extent of fractures in the skull.

Carson, R.C., Butcher, J.N., & Mineka, S. (1996). Abnormal Psychology and Modern Life, tenth edition. New York: HarperCollins.

Freeman, E.A. (1987). The Catastrophe of Coma: A Way Back. Queensland, Austrailia: David Bateman Ltd.

Ivan, L.P. & Bruce, D.A. (1982). Coma: Physiopathology, Diagnosis and Management. Springfield: Charles C. Thomas.

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