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Encephalographs designed for recording the variations of the electric potential caused by the electrical activity of the brain, usually detected on the scalp. These recorders consist of a main unit that includes memory (e.g., strip chart, flash card), signal processors, and a cable that is connected at the distal tip through a head box (amplifying unit) to a set of electrodes. The electrodes are typically placed on a cap or net fixed on the scalp in an array of standardized positions. Intracranial electrodes are used in very specific procedures. The electrodes and leads transmit the bioelectrical signals to a recorder which is capable of storing their characteristics for later display in an amplitude versus time graph (i.e., an electroencephalogram); some recorders can also provide a spectral analysis of the signals using a dedicated firmware. Electroencephalographs (EEGs) are used to help in the diagnosis of neurological diseases (e.g., epilepsy), to assist in localizing tumors and lesions inside the cranium, and also facilitate the assessment of the status of patients (e.g., coma, brain death). Ambulatory and dedicated computerized EEG recorders intended to provide further analysis of EEG data and also from data taken from sleep disorder studies and/or to evaluate the electrical response of the brain to external stimuli (i.e., evoked potentials) are also available. EEGs are not intended for a real-time assessment of the electroencephalogram or other brain conditions.
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Recorders designed to measure and record data and graphics of the physical and/or functional characteristics of the brain. Encephalographs are usually intended to record one or several of the following data and graphics: (1) electrical potential caused by the electrical activity of the brain (i.e., electroencephalographs); (2) electrical activity of the brain due to the application of external stimuli (evoked potentials); (3) biomagnetic field caused by the electrical activity of the brain neurons detected externally to the body (i.e., magnetoencephalographs); (4) ultrasonic signals reflected by the brain and surrounding tissues (i.e., echoencephalographs). Encephalographs are intended for evaluation of recorded information of the brain and central nervous system conditions; they are not intended for real-time assessment of those conditions. Other devices, such as neurologic monitors and image scanning systems (e.g., MRI, CT) are also used to evaluate brain conditions and disorders.
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