Basic instrumentation Flashcards
Electrode impedance
<5000 Ohms
to stimulate we use anode and cathode electrodes, but for recording we use?
Active (+) and Reference (-)
Define gain
Gain- the amount that a differential amplifier amplifies the difference between the incoming voltages. Gain=output voltage/input voltage. (Vin= Reference-Active)
Define Common mode rejection (CMR)
signals that are identically received by both inputs to the amplifier are rejected. Helps eliminate noise.
Define common mode rejection ratio
how well a differential amplifier rejects common mode signals. 10,000:1 or 80 dB
The input impedance should be?
Measured across the amplifier and > 10 MOhms
Concepts of Fourier Spectrum and frequency domain.
Fourier Transform- math formula that calculates the frequency content of a signal. Time domain signals are converted to frequency domains. Frequency Spectrum- describes the composition of a signal in terms of individual frequencies that make up the signal.
What is the function of locut and hicut analog filters?
To eliminate unwanted high and low frequency. Decrease hicut=longer wave, increase locut= shorter wave, “lower means longer”
Cutoff frequency
Signal is reduced by 3dB or 30 %
60 hz notch filtering
Cuts out one frequency from spectrum, get ringing effect in trace proportional to the size of the stim artifact.Can use in EMG but should not use in SSEP due to ringing artifact.
Analog v. Digital filter
Digital Filters- produce no phase effects, reversible (smoothing)
Analog Filters- uses resistors and capacitors to filter the analog signal. Can create phase effects.
Define Sampling rate
Number of data points collected/second
Define Analog
Continuous sample in amplitude and time
Define Digital
Discrete values (sample has specific amp and time)
Define Bin
Interval time that sample is taken in.
Define Dwell Time/Band width
Time between samples.
Bin Width= 1/ sampling frequency
Define Nyquist Frequency
2 x the highest frequency of recorded signal
Aliasing- misrepresentation due to slow sample rate (below the nyquist)
Define Horizontal Resolution
Want fast sampling frequency
Bin width- 20mcsec/data point
Sample Rate- 50 KHz
Define Vertical Resolution
Number of Voltage values= 2^N N= number of bits
Must have 8 bits
Define Range
max and min voltages. Must accommodate signal being recorded. Squaring occurs if range is too low resolution if range too high SSEP –1 mcV to 500 mcV (+- 500mcV) EMG- 300 mcV to 10 mV (5 mV) TcMEP- +- 10 mV
Understand the Signal averaging process, including the assumptions that make it work, and how it affects signal to noise ratio.
Noise is random so its mean signal will be zero
Evoked Potential signal is constant in latency and morphology (repeats)
Records several traces and then averages them to see the repeatable responses
Understands the process of artifact rejection and its application to averaging.
Sweeps that contain signals way outside do not get counted (completely erased) if intermittent
Understands the concept of Display Gain, Scale and Sensitivity.
How the gain of the amplifier is displayed on the screen
Sensitivity- (up and down arrows) microVolts/division
Amplitude = (number divisions)(sensitivity)
Timebase- (left and right arrows) mS/division
Latency= (number divisions)(time base)
Understand the relationship between stimulus repetition rate and analysis period (sweep) and the factors that influence the choice of rep rate.
Stimulus Repitition Rate- stimuli delivered / second (4.47) no factors of 60
Analysis Period- (sweep) 1/ rep rate
Max Rep Rate= 1/(sweep times + lag times)
