EEG and MEG   




What is Computerized Axial Tomography? 

          A CAT scan is one of the two most employed methods (along with MRI) for visualizing the brain and evaluating possible intracranial abnormalities. Though CT scanning has been available as a diagnostic tool for only about 25 years, remarkable advances have been made with the technology, including improvements in image quality and system capability.  A CT scan is essentially a computerized assembly of several x-ray images taken from a series of different angles. With a CT, the resolution is much better than conventional x-rays, and the detail that can be seen is much greater. 

        As with all other typical x-rays, the procedure is radiographic and the patient's body is exposed to a small amount of radiation during the scan.  The equipment necessary for a CT scanner include the gantry, x-ray source, detection system, computer, and display network.  The gantry is a donut shaped structure in which a table (where the patient lies) extends into the "donut hole".  Within this structure is the x-ray source and detection system. The x-ray system moves around the patient being scanned and operates in a manner that ensures only thin cross-sectional slices of tissue are evaluated at a time.  The detector, exactly opposite the x-ray source, measures the amount of radiation that is unabsorbed as it passes through the skull and brain tissues. When enough of these x-rays are gathered, the full image is reconstructed by the computer and sent to the display network for immediate evaluation and storage on a computer disk.  Tumors, lesions or tissue damage will show up as areas of altered density when the image is evaluated. 

        A patient going in for a CT scan will encounter basically a similar setup of equipment.  They will be asked to lie still on the table with the head gently held secure by straps in the gantry.  Either the table or the scanner itself will move around the patient to ensure that x-rays from many different angles are taken.  The test usually causes little discomfort and typically lasts 15 to 30 minutes. Depending on the type of scan being taken, a contrasting agent may be injected into the patient's blood vessels or swallowed before the scan is run.  This is done to enhance contrast in the image by accentuating differences between normal and abnormal tissue. 

        A contrasting agent is usually not necessary in cases of acute head trauma or stroke.  When a contrasting agent is necessary, the agent used is a safe and harmless substance for most people to use. However, the patient may experience side effects such as feeling flushed or a temporary headache or nausea after injection.  Sometimes allergy to the contrast media is one of the risks associated with CAT scan.  A patient that has had allergic reactions to medications in the past should talk with their doctor about this potential risk.  The only other risk the could be of concern to the patient is the extent of radiation.  As with any type of radiation, exposure to body tissues should be limited, as large doses can be dangerous.  The amount of exposure during this procedure is minimal, however, and should not be threatening.  Pregnant women, as exception, should not have a CT scan without first discussing risks with their doctor. 

        A patient may need to receive a CT scan for one of several different reasons.  A scan may be beneficial for finding tumors and abnormalities within the brain, to monitor the effects of surgery, radiotherapy or chemotherapy on brain tumors, to detect possible blood clots after head injury, or to check the brain's function.