II D digital instrumentation Flashcards
HFF makes muscle artifact look like
Beta
evolution
gradual change in amplitude frequency or spatial distribution of rhythm
60 Hz
Notch filter
common mode rejection
ACNS guideline: 90 Db
EEG amplifiers
Common mode rejection
- the ability of an amplifier to reject like signals
- differential amplifier
60 Hz filter has the greatest effect on
16 msec waveform
voltage resolution
analog to digital converter
time constant
LFF
input impedance
high
differential amplifier
magnifies common-mode voltage difference
differential amplification
info from 2 inputs and amplifying the difference
Nyquist theorem
minimum sampling rate
2X the frequency of the highest waves
eX: HFF: 70 Hz min sample rate: 210
ACNS guideline: 3x the HFF
frequency response curve
filters
frequency response curve
sharpness is determined by the roll off
double the inter-electrode distances
higher amplitude
frequency
Hz
frequency
sampling rate
system gain
ratio of amplifiers to output to the input signal
fast Fourier transform
converts time function into sine waves of different frequencies
long time constant
LF .1 Hz
time constant of .5 sec
LF .3 Hz
ground electrode EEG
FPz
delta wave best seen with filter
time constant 1.0 sec
voltage resolution
analog to digital
HFF of 15 Hz, what percent of amplitude is visible?
.7
time constant for 3 Hz
.05 sec
sampling rate for HFF of 70Hz
210 psec
eliminate cortical spikes
change HFF from
70 Hz to 15 Hz.
3 Hz wave attenuated by what percentage of .3 Hz filter?
.3
LFF is changed from 1 Hz to 5 Hz.
How is 2 Hz wave affected?
significantly attenuated
LFF of 5 Hz will attenuate a 5 Hz wave
.3
time constant for 3 Hz
.05 sec
.5 Hz was is enhanced without affecting spike with this filter:
LFF .3 Hz
signals with like frequency, amplitude and phase
are canceled
vertical resolution
amplitude
sampling rate
a signal sampled at intervals and assigned a numeric value
When a 60 Hz sine is sampled at 100 Hz
aliasing
long time constant
LFF .1 Hz
A/D converter
converts analog signal into digital binary numbers
high sampling rates
smooth connected lines
ACNS guidelines for horizontal resolution
16 bits
ability for amplifier to reject like signals
common mode rejection
low sampling rate causes fast frequencies to appear slower
“undersampling”
aliasing
input 1: +50 muV
input 2: -100 muV
what’s the output voltage and deflection?
150 downward
Not useful in digital EEG
biocal
most sensitive
2 Uv/mm
clipping of the waveforms happens
signal is outside of the range of the digitizer
EEG amplifiers
differential
amplification
increasing the # of seconds on monitor
No Change in
Spike
amplitude or
duration
digital EEG montages are reformatted usijng
system reference
sensitivity
the amount increased by differential amplifier to
magnify
input signal
a filter
alters the amplitude of frequencies
