Introduction to EEG Technology
•Electroencephalogram (EEG) – is the study of the electrical activity of the brain in the form of waves recorded from the brain with the use of either an analog or digital EEG medical equipment. It was first discovered by Hans Berger(a German neuropsychiatrist) who started it with a dog in 1902 and in humans in 1920.
Sample of the old ANALOG paper EEG RECORDING
•EEG is being used world-wide and available in most hospitals and medical clinics especially in neuropsychiatric and respiratory departments.
•EEG is being performed by certified EEG Technicians with at least 6 months practice with supervision or technologists(professionals) with the use of analog or digital computers. This tutorial workshop only serve as an introduction to Electroencephalography. You need to go for further studies to qualify and be certified.
•A neurologist or a physician with board eligibility or certification in neurology, pediatric neurology, neurosurgery, or psychiatry mainly reads or interprets the EEG and he is referred to as an Electroencephalographer. Training should meet the minimum requirement for exam by American Board of Clinical neurophysiology.
Uses and Importance of EEG
EEG is very useful in the understanding and diagnosis of brain-related disorders and problems including diagnosis of epilepsy and detection of its causes, to research sleep disturbances, to detect and locate tumor, infection, or injury in the brain, to detect and evaluate stroke, to diagnose certain types of spinal meningitis, to detect bleeding in the brain, to diagnose and analyze degenerative disease such as Alzheimer’s, to monitor brain function during surgery and evaluate the degree of anesthesia, to analyze comatose patients, to distinguish psychiatric conditions from neurological conditions, to predict whether an individual is likely to have a seizure after a head injury, to confirm brain death in comatose individuals. It should be noted that this decision is always supported by other tests and corroborated by a specialist.
EEG records electrical brain activity or brain waves such as:
•Delta (less than 4 Hz)
•Theta (4-7 Hz)
•Alpha (8-12Hz) most prominent within the occipital region of the scalp
•Beta (13Hz and above)
EEG electrode placements are based on 10-20 or the 10-10 International Head measurement.
Even numbers represents the right hemisphere and odd numbers on the opposite side as follows:
Fp1 stands for Prefrontal region Fp2,F7Anterior TempF8, T3(T7)Mid tempT4 (T8),T5, (P7)Posterior TempT6 (P8), 01 Occipital 02, F3 FrontalF4, C3 CentralC4, P3 ParietalP4, FPZ Prefrontal vertex, CZ Central Vertex, FZ Frontal vertex, PZ Parietal Vertex.
EEG cup electrodes using EEG paste, collodion or EEG electro-cap using gel may be used in EEG recording. However, proper electrode placement should be strictly observed for accuracy. The scalp must be clean and skin prepared before electrode placement based on the International 10-20 or 20-20 system.
EEG montages or patterns based on the International 10-20 or 20-20 system must be used in EEG recording. The acceptable EEG montages include the bipolar, sagittal and parasagittal, transverse, ear reference, CZ common reference and average patterns.
The minimum number of EEG channels is now 16 channels with optional EKG, EMG, EOG and respiratory channels as may be required.
EEG recording should utilize a paper speed of 3
cm/sec. or a digital display of 10 seconds/page. For special situations like in newborns, 1.5
cm/s or 20 s/page may be used.
Knowledge and proper training on Digital EEG equipment, instrumentation and standard EEG settings on sensitivity or gain,filters and impedance are a must for accuracy and reliability of EEG recording.
Minimum of 25 minutes EEG recording must be performed. Additional minutes may be needed with Photic stimulation, Hyperventilation and optional sleep recording.
Hyperventilation is an evocative technique performed in routine EEGs for three minutes and three minutes post HV using a longitudinal bipolar EEG montage. It is performed unless contraindicated like in patients with heart or lung problems.
Photic stimulation is another visual evocative technique routinely performed in EEG with flashes ranging from 1 to 30Hz or more as may be necessary with eyes closed and half open. Longitudinal Bipolar EEG montage is usually utilized. It is performed to check patient's photosensitivity and to rule out brain-related abnormality.
Understanding of clinical conditions and correlates is very essential in EEG recording to understand and meet the goal and benefits of doing the test.What brain disorder needs to be ruled out or confirm? Is the patient really suffer from epilepsy? If so, what kind of epilepsy?
Digital Wake EEG
Neonatal EEG patterns
Active and quiet sleep are normal sleep patterns in neonates and term infants.
Active sleep EEG pattern is characterized by rapid eye movements, frequent body jerk movements, atonic facial EMG with occasional smiling or grimace, suckling and brief apnea, and irregular respiration and heart rates.
Quiet sleep EEG pattern - during this stage there is decrease in eye and gross body movements, regular heart rate and respiration, with tonic facial EMG.
SLEEP EEG PATTERNS
Sleep spindles, vertex sharp waves, K-complexes, Positive Occipital sharp waves (POSTS), Hypnagogic hypersynchrony are some of the normal sleep patterns that may be observed in EEG recording,
Sleep spindles appear in quiet sleep as early as 40 weeks CA which may be asynchronous or shifting asymmetry until age 2 years. They may look sinusoidal, comb-shaped, or spiky when appearing with vertex sharp waves predominant in central and parasagittal regions.
What are the two evocative techniques utilized in EEG recording?
Is apnea briefly seen in a neonate's active sleep EEG pattern?
What stage of consciousness do you observe POSTS?
What is EEG, its importance or Uses?
What are the standard settings for sensitivity, time constant, high frequency filter and paper speed for routine EEG recordings?
What is the minimum number of minutes required for baseline EEG recording?
What is minimum range of photic stimulation flashes/second when performing it in EEG recording?
Who is authorized to read and interpret EEG recordings?
What board exam is required to become a professional in EEG? (slide 3)
When is hyperventilation or overbreathing not performed in EEG recording? AT At least how many montages should be used in EEG recording for 16 channels?
What is the importance of adding ECG channel in EEG recording?
To learn more information about EEG and other fields of neurophysiology, please visit our website regularly for updates
NERVE CONDUCTION STUDIES (NCS)
A simple and a reliable tests to evaluate peripheral nerve function.
Used to assess the severity of pathology and to localize the site of maximal involvement
The nerve is electrically stimulated to initiate an action potential which travels along motor, sensory or mixed nerves.
The conduction time can be measured by recording the potential either from the muscle innervated by the motor nerve or from the nerve itself in the case of sensory or mixed nerve conduction.
NCS is a neurodiagnostic test for the diagnosis of nerve diseases including Carpal Tunnel Syndrome and many others. Below are the common nerves that are usually tested:
- Median Nerve
- Ulnar Nerve
- Radial Nerve
- Peroneal Nerve
- Tibial Nerve
Short Quiz: What is electrically stimulated to initiate an action potential?