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EEG Terms

2

QuestionAnswer
Paper Speed Definition The amount of paper used or a particular period of time. This speed is equal to 1 second.
5 small divisions on paper equal... 200 msecs.
2 seconds recording time equals... 200 msec for 30 mm/sec, 100 msec for 15mm/sec and 400 msec for 60mm/sec.
1/2 second recording time equals... 100 msec for 30 mm/sec, 50 msec for 15mm/sec and 200 msec for 60mm/sec.
Nyquist Criteria The sampling rate must be at least twice as fast as the fastest frequency being recorded. 3-4 times as fast is ideal for digital conversion. This is measured in Hz. Ex: 256 Hz.
Aliasing This occurs when there are not enough digitalized points made on the wave for accurate digital conversion and some faster frequencies may be missed.
Amplification Enlarges tiny electrical signals coming from the brain so they may be displayed on paper or digitally.
Differential Amplifier The output voltage is equal to the difference between the input voltages of G(rid) 1 and G2. Amplifies the difference between two voltages but does not amplify the particular voltages.
Hans Berger established... EEG frequencies in 1929.
Spikes have a duration of... 20-80 ms.
Muscle artifact have a duration of... Less than 20 ms.
The absence of alpha activity in one hemisphere is always... Pathological.
Alpha assymetry is almost always due to poor... Electrode placement.
This should always be present in a recording and seen mostly in the fronto-centro head regions and sometimes diffusely and is not reactive to EO/EC... Beta activity.
These medications can enhance beta activity... Barbituates, Benzodiazephines, Chloral Hydrate, Antidepressants.
Montage Types... Longitudinal Bipolar (LB) Transverse Bipolar (TB) Referential
Which hemisphere goes first in a montage? Left.
Which head region goes first in a montage? Anterior.
Which head region goes last in a montage? Posterior.
Which hemisphere goes last in a montage? Right.
Average Reference Uses tech's choice of one lead and each channel is calculated individually based on distance from that lead.
Source Derivation (Laplacian) Averages surrounding leads and compares that to the center lead in that particular group. (Most sophisticated reference)
60 S/P Slow - Gives more time to cover a second. Spreads waveforms out. Good for spreading faster frequencies.
30 S/P Normal recording speed.
15 S/P Fast - Less time used to cover a second. Condenses wave forms. Good for condensing slower frequencies.
Types of Electrodes: Surface, Needle, Depth/Grid, Nasopheringeal (NP), Spenoidal, T1&T2.
Bipolar Montage (Directional): Linked anteriorally to posteriorally. There are two types.
Double Banana (DB): One type of bipolar montage linked from left to right. This can be done in blocked form or alternating.
Referential (Longitudinal) One type of bipolar montage linked individually to a reference. This can be done in blocked form or alternating. G1 will be different in every channel, G2 is the same in every channel.
Types of Bipolar Montages: DB/Longitudinal (L to R blocked or Alternating), Transverse (side to side), Circumferential (Hat Band).
Types of Referential Montages: Longitudinal (L to R blocked or Alternating), Ears, CZ, Average Reference, Laplacian, Ipsilateral Ears.
What type of Montage does a digital recording always use? Referential.
What type of recording should you not use a CZ reference for? Sleep.
What are Ear References known for picking up? EKG artifact.
What are some results of bad electrode placement? Amplitude Assymetry, Cancellation Effect, Inaccurate Dx.
Why are referential montages usually high amplitude? Due to the distance between the active and inactive lead.
Derivation: The order of selection pairs that determine the electroanatomical picture.
Montage: An arrangement of electroanatomical pairs.
Baseline: Electrical Zero.
What is the Circumferential (Hat Band) best for recording? Frontal and occipital activity.
LFF Commonly used to attenuate spikes and enhance faster frequencies. *This filter is also known as the Time Constant.
Time Constant (TC): The time in seconds required for the signal to attenuate by 37% of it's original value. Standard is 0.3-1.0 seconds.
Inferior Coronal Montage: The central and temporal regions are transversed to ears with the ears linked.
What is the Inferior Coronal Montage good for? Brings out low voltage activity at the temporal head regions.
The main effect of a filter is: To attenuate (lesson) a specific frequency a range of frequencies.
HFF Commonly used to attenuate muscle activity.
Frequency Response Curve: It represents that 80% of that particular frequency will be seen with filters set at 70 HFF and 1 LFF. Frequencies out of that range are affected based on the curve. This is the same for both the LFF and the HFF.
Biocal: Checks the integrity of the hardware and the pt.
Mechanical Baseline: Checks the space between pens in chart mode during movement of the paper recording.
Electrical Baseline: Measures spacing between pens when switching modes.
Pen Damping: The amount of pressure the pens use, measured by how round or how sharp the tip of a signal wave is.
Time Axis: The point where the pens take off in a square calibration signal.
Pen Deflection: The height of a calibration signal.
Polarity: Which way the pen will deflect.
Differential Amplifiers can also produce: Cancellation and Summation.
Cancellation: 2 inputs with similar activity outputs a very small difference and very low amplitude.
Summation: 2 inputs with very dissimilar activity; the difference will be large and the output will be high amplitude.
Spacing Inaccuracy: The output may be the amount of difference, rather than the true activity in that area.
Grid Convention: An upgoing deflection indicates that input 1 / Grid 1 (G1) is more negative (or less positive) than input 2 / Grid 2 or (G2). There are 3 other formulas but they follow the same suit.
Localization: Is found by Greatest Amplitude or End of Chain activity.
Polarity Principles: Differential Amplifier, Grid Convention, Localization.
Polarity is mostly necessary for... Localization of abnormal activity.
If G1 is more negative than G2... The pen will deflect up.
If G1 is more positive than G2... The pen will deflect down.
If G2 is more negative than G1... The pen will deflect down.
If G2 is more positive than G1... The pen will deflect up.
If G1 & G2 are =: No deflection (Cancellation).
Most abnormal activity has which polarity? Negative.
If both inputs are negative... Add the numbers together and then put a - sign in front.
If you are subtracting a positive number... The result will be more negative.
If you are subtracting a negative number... The result will be more positive.
How do you find the absolute difference on a number line? Count the numbers in between.
Supraotbital (SO): Above the eye.
Infraorbital (IO): Under or below the eye.
Which part of the eye is more positive? Cornea (anterior).
Which part of the eye is more negative? Retina (posterior).
What is usually out of phase (reversal / more negative) with brain activity. Eye movement (EM).
What is usually in phase with brain activity and higher amplitude? Glossokinetic artifact.
Upward deflection is: Depolarization.
Downward deflection is: Repolarization.
Time is expressed as: Frequency.
Where do brain waves come from? Cortex.
What voltage is beta activity usually? Low.
What does Digital Calibration only calibrates? Amplifiers.
How many additional electrodes does digital recording require? One.
Analog to Digital Converter (ADC): Takes raw EEG signal and assigns data points to allow the computer to manipulate the data.
Analog Grid: Individual electrodes are placed in each grid of the amplifier.
Digital Grid: Different electrodes are placed in G1 and then G2 remains the same for all channels. This allows for montages to be reformatted.
What does the reference input do? Cancels out the difference in a particular montage that is being displayed.
3 Landmarks (planes) in 10-20 System: Sagittal, Coronal, Horizontal.
Sagittal Plane Measurement: Nasion to Inion. Makes up the central dividing line of hemispheres.
Coronal Plane Measurement: Pre-auricular to Pre-auricular. Makes up the central dividing line of anterior and posterior.
Horizontal Plane Measurement: Division of all 3 pairs of central lines from the 10% mark. Divides the circumference.
D Deflection, Distance, or Duration
Standard References Ipsilateral Ears and Cz
In polarity, if all leads show the same amplitude, which is contaminated? Reference
Which way will a negative amplitude deflect at the end of a chain? Down
What pattern do you see in the frontal region with mental activities? Rhythmic Theta
Voltage of Alpha: 20-200 uV
Voltage of Beta: 5-10 uV
Voltage of Delta: 20-150+ uV
Voltage of Theta: 10 uV
What are the 3 most commonly used Activation procedures? HV, PS, and Sleep (deprivation).
What is another maneuver that can elicit abnormalities in certain susceptible individuals? Reflex Epilepsy
How long should HV be used for? 3-5 minutes
Anxiety, light-headedness, tingling (more around fingers and mouth), unreality, coldness, sweat, breathing. Symptoms that can be brought out by HV.
Contraindications of Hv Cardiac problems, Recent Stroke, Recent TIA, SAH, Chronic Pulmonary Disease, COPD, MI, Sicle Cell Anemia, AVM, Aneurysm Hx, Pregnancy, Extreme Hypertension, Recent Intracranial Surgery.
If a phase reversal occurs in a referential montage, it is a... Contaminated reference.
What do you use to find the focus in a referential montage? Greatest Amplitude.
What do you use to find the focus in a bipolar montage? Phase Reversal or End of Chain.
What is it if it the focus is only showing in one channel of a bipolar montage or 2 channels in a reference montage? Bad Electrode.
What unit measures how often a wave occurs? Frequency.
What unit measures how long a wave occurs? Duration.
What unit measures the power of a wave? Voltage.
What unit measures the height of a wave? Amplitude.
What term is used to describe the shape of a wave? Morphology.
Quiescence A state of quietness or inactivity.
What is the duration of a sharp wave? 80-200 ms.
What is another name for the HFF? Low pass filter.
Isopotentiality 'Flat line.' Used in ECS.
Lateralized (Recorded in) Both hemispheres.
Nasopharyngeal Electrodes Inserted through the nose adjacent to the spheroidal bone. Records innermost temporal activity. Discontinued due to unavoidable artifact.
Spenoidal Electrodes Inserted with a hollow needle through the spheroidal notch of mandible and records the innermost temporal activity.
End of Chain Polarity No phase reversal will be apparent.
Bell Curve (Gaussian Distribution): Symmetrical curve that represents distribution of values, frequencies, or probabilities. It slopes downward from a point in the middle corresponding to the mean value/maximum probability. The 'Gaussian' normal distribution is mathematically well-defined.
What is the Bell Curve representing in EEG? Filters.
Paroxysmal Without warning and without preceding provocative events.
Non-Epileptic Not generated primarily by the brain.
What are the Prolactin levels in diagnostic determinations of szs? Occurs in the post ictal phase (20-25 m after sz subsides). Most consistent increase after GTC: 1-2 fold from baseline 90-100% of pts. CP: 43-100%, SP: 10%. None after Absence or NES.
What is Callosotomy? Severing the corpus callosum so that communication between the cerebral hemispheres is interrupted (in cases of severe intractable epilepsy).
How are depth electrodes implanted? A stereotactic headframe is affixed to the pt's skull with pins, then CT or MRI scanning of the head performed. Target sites for placing electrodes are selected using the stereotactic imaging studies. This technique is extremely precise in localization.
Notch Filter Designed to filter out a single frequency, but has an effect on surrounding frequencies as well. 60 Hz in U.S. Most commonly used to filter out electrical interference. Can also effect spikes in this range.
What measures the Time Constant? Distance / Paper Speed
Amplification The electronic processing of very small voltages so that they control much larger voltages and current, which can be more easily measured.
Differential Amplifiers (In EEGs) Amplifies only the difference in voltage between 2 inputs, neither of which is ground potential.
What is the cut off frequency in EEGs? 70-80%
Does the output with LFF make it look like it occurs later or earlier in time? Earlier.
Does the phase shift that occurs with the HFF appear to be occurring earlier or later in time? Later.
Ink-Writing Recorders Output voltages of an EEG are applied to a galvanometer, which carried an ink-writing pen.
EEG Insturment Reproduces faithfully at it's output the voltages generated by the brain.
BSSW Bilaterally Synchronous Spike and Wave Discharges.
The receptacles in the electrode board are called... Jacks.
Connecting the electrodes to the amplifiers is the ... Electrode selector.
Output is... The permanent visible EEG record.
A derivation is... The electroanatomical picture of the brain.
The amount of microvolts to produce 1 mm. of pen deflection is... Sensitivity.
The chart drive... Adjusts speed of recording paper beneath the pens.
Input The point at which the voltage at the scalp enters the equipment.
Jackbox / Headbox Electrode board where electrodes are plugged into small receptacles called jacks.
Terminal Pin Inserted into Jacks and has either numerical or anatomical identifications for points on the head.
Input Cable Connects each electrode to a specific point.
Electrode Selector The specific point where electrodes are connected. Composed of rows of push button, slide, rotary, or other switching devices that connect electrodes to amplifiers.
Input Terminals Grid 1 is the top switch of the pair and Grid 2 is the lower switch of the pair, used to select the pair for the derivation. At least 23 selections needed.
Derivation The order of pair selections that determine the electroanatomical picture of the brain that will be displayed on the EEG instrument.
Master Electrode Switch The switch used to change the entire montage.
Montage The arrangement or map of the electrodes.
How many electrode inputs must there be? 23
Calibrator Used to apply a pre-selected voltage simultaneously to all inputs and outputs of amplifiers within the range of EEG activity.
What is the range of EEG activity? 2 uV-1 mV.
Amplifiers Processes extremely small signals from the brain so the voltages can be given significant power for graphic recording.
Sensitivity Microvolts (uV) of input required to produce 1 millimeter (mm) of pen deflection as an output.
Main Sensitivity Adjusts each channel sensitivity and changes overall sensitivity from uV/mm to mv/cm (more sensitivity).
Establishes low frequency recording limits. LFF.
Establishes high frequency recording limits. HFF.
Baseline Adjust Control Makes it possible to center baseline of each channel at 'Electoral Zero.'
Master Control Settings Changes any of the principal control functions simultaneously in all channels (sensitivity, LFF, HFF, 60 Hz filter).
Chart Drive Adjusts the speed of the paper beneath the pens (mm/second - 30, 60, 15).
Ink Writing Galvanometers Provides the write-out of the EEG record. A moving coil in a magnetic area moves the pens.
What type of 'bit' rate produces the best wave resolution? The more, the better.
What should the screen resolution be? At least 64 Hz / 1280 pixels. The more the better.
Networking Connecting several recording units to a reader unit, printer, etc.
Storage Meduim Magnetic tape, Optical disks, CD, DVD.
Reformatting With mathematical equation-ability to re-figure electrode selections due to use of a Reverence and Common Mode Rejection.
Digital to Analog Conversion (DAC) Changing the data from 'numeric' back to a continuous waveform.
Horizontal Dipole A field of an EEG waveform in which the waveform is simultaneously present as a + over one head region and a - over another. Phase reversal in a referential montage.
Longitudinal Montage Anterior to Posterior.
Transverse Side to side or circumferential.
Who in responsible for selecting the montage and instrument settings? It is the EEG Tech's sole responsibility.
Electrodes Step-By-Step - 1 Surface
Electrodes Step-By-Step - 2 Needle
Electrodes Step-By-Step - 3 Depth/Grid
Electrodes Step-By-Step - 4 Nsayopherengeyl
Electrodes Step-By-Step - 5 Sphenoidal
Electrodes Step-By-Step - 6 T1 & T2
Bipolar Referential Montages Ears, Cz, Average, Laplacian, Digital System.
Directional Montages Longitudinal, Transverse, Alternating.
Extra Electrode Placements - Between F7 & F3: F5
Extra Electrode Placements - Between F3 & Fz: F1
Extra Electrode Placements - Between Fz & F4: F2
Extra Electrode Placements - Between F4 & F8: F6
Extra Electrode Placements - Between T3 & C3: C5
Extra Electrode Placements - Between C3 & Cz: C1
Extra Electrode Placements - Between Cz & C4: C2
Extra Electrode Placements - Between C4 & T4: C6
Extra Electrode Placements - Between T5 & P3: P5
Extra Electrode Placements - Between P3 & Pz: P1
Extra Electrode Placements - Between PZ & P4: P2
Extra Electrode Placements - Between P4 & T6: P6
What should you do when measuring to accommodate for a scalp deformity? Measure from the pre-auricular point on the normal side of the head to Cz (assume it is 18 cm). Double that figure (36 cm) and use that total as the distance between the pre-aur landmarks to calculate the temporal and central locations on normal side.
Gain The ration of the output signal of the input signal (or) the amount of magnification being used to amplify or increase the voltage of a signal.
Created by: kmburg5840