Sometimes referred to as the "brain wave test," an EEG records the electrical activity of the brain. EEGs are performed on patients who have experienced seizures, epilepsy, passing out, headaches or brain attacks (strokes). An EEG can also be performed to determine the level of consciousness of a patient, mental status changes and for determination of brain death.
To perform an EEG, small metal disks are attached with a conductive cream to the scalp of the patient. The patient is asked to lie quietly for 20-30 minutes while data are being recorded. During the recording, the technologist will ask the patient to open and close his or her eyes, perform hyperventilation (breathing faster and deeper than usual), look at a strobe light, and go to sleep. These procedures enable the technologist to obtain detailed information for interpretation by the physician. The entire procedure, including patient set-up, takes approximately two hours. An EEG is also the basis for long-term monitoring for epilepsy.
This EEG is differs from a routine EEG (above) in that the patient wears electrodes home for up to one week so that more information can be gathered. The electrodes feed data into a small recorder that gathers information over the 24-hour period. During an ambulatory EEG, the patient wears electrodes attached to the scalp to monitor brain waves, and the chest to record the heart rate. The patient comes back to the hospital for removal of the electrodes. The data in the recorder is then processed and interpreted by the physician.
Long-Term Monitoring for Epilepsy (LTME)
Epilepsy patients are observed through the use of an EEG with simultaneous video monitoring. This is done to document seizure activity over an extended period of time. The patient is admitted to the hospital to monitor his or her safety and to observe his or her events. Patients typically remain in the Epilepsy Monitoring Unit for four days.
We are very proud of the Epilepsy Monitoring Unit, which is the first community hospital based inpatient epilepsy unit in greater Baltimore. It opened in the fall of 2005.
Evoked Potentials (EP)
The EP provides a measurement of how long it takes an impulse to travel from a point of stimulation to the brain. There are three modalities, or types, of EPs: Brainstem Auditory Evoked Response (BAER), Visual Evoked Response (VER), and Somatosensory Evoked Potentials (SSEP) of the arms or legs. Evoked potentials are performed to detect and determine the severity of multiple sclerosis, spinal cord injury or disease, and brainstem injury or disease. Evoked potentials may also be used to determine brain death. To perform an EP, small metal disks are attached to the scalp and to various places along the path of the nerve being tested. The time needed to perform an EP varies, depending on the modality being done. It can take approximately two hours, including patient set-up, to perform one type of evoked potential. When performing multiple modalities, four to six hours may be needed.
Electrocorticography is performed to take recordings directly from the surface of the brain through special electrodes. This is done to localize the exact area of abnormal seizure activity arising from the brain.
Intraoperative Monitoring (IOM)
Because surgery involving the nervous system is delicate, neurodiagnostic modalities can be used to ensure patient safety during surgery. The electrical activity of the central nervous system is monitored while the patient is undergoing surgery. The electrical activity from the brain, brainstem, spinal cord and/or peripheral nerves is recorded, especially when there may be a risk to vital neurological structures (such as the brain or spinal cord) during surgery. EEGs, EPs, ECOG and electromyograms (to detect muscle innervation) are commonly performed during surgical procedures.