Fisch EEG Primer Chapter 3

Question 1

EEG frequency range of greatest clinical significance

Answer 1

0.5-30Hz

Question 2

Aliasing results from..

Answer 2

sampling analog signals LESS than at least TWICE (Nyquist theorum and rate) as fast as the fasted freqency contained in the analog signal.

Question 3

Difference between the electrode input board (aka jackbox, input box) of an analog vs. digital EEG instrument

Answer 3

analog: receives input and then transfers to amplifier
digital: receives AND amplifies signal before sending to computer monitor

Question 4

Each channel of the EEG recording is producted by the output of one differential amplifier which measures…

Answer 4

difference in voltage between its two input terminals. Negative differences (greater negativity at input 1 compared to input 2)deflect UPWARDS and positive difference (greater negativey at input 2 compared to input 1) deflect DOWNWARDS.

Question 5

Digital Filtering involves…

Answer 5

suppression of waveforms in selected frequency ranges

Question 6

Montage reformatting involves..

Answer 6

retrospective changing of the displays montage

Question 7

Purpose of EEG amplifiers (2)..

Answer 7

• differential discrimination of differences in electrical potnetial of input 1 and 2
• amplify size of potential differences

Question 8

Differential discrimination/amplification (performed by amplifiers) involves

Answer 8

inputs 1 and 2 are essentially amplified in opposite directions from the amplifier ground, and effectively subtracted

Question 9

In differntial amplification, a single waveform output can be the result of

Answer 9

an infinite number of different inputs

Question 10

What is the difference between impedence and resistance

Answer 10

resistance involves direct (constant voltage) while impedence involves alternating currents.

Question 11

60 Hz interference can be seen when…

Answer 11

unequal electrode impedence is present - most commonly results from loss of contact between electrode and scalp

Question 12

Absent or ineffective ground connection results in…

Answer 12

lack of reference to polarize inputs 1 and 2 and results in amplication of artifacts that would otherwise be ignored
NOTE: does not protect patient from electrical shock

Question 13

Amplification is characterized in terms of sensitivity which is measured by…

Answer 13

sensitivity: microVolts/mm (typical 7)

Question 14

Low frequency filter (a.k.a. High pass filter)

Answer 14

reduces the amplitude of slow waves - decreases amplitude of selected frequency range 20-30% and then logarithmic filtering at even lower frequencies

Question 15

High frequency filter (a.k.a. Low pass filter)

Answer 15

reduces the amplitude of fast waves - decreases amplitude of selected frequency range 20-30% and then logarithmic filtering at even higher frequencies

Question 16

Notch filter

Answer 16

selectively reduces a narrow frequency range in order to remove electrical interference (i.e. in North America typically set to 60Hz)

Question 17

Three key attributes that determine how wll an analog to digital converter (ADC) will work…

Answer 17

1) sampling rate
2) number of amplitude levels (amplitude resolution) that can be resolved
3) input voltage range