Basic instrumentation

Question 1

Electrode impedance

Answer 1

<5000 Ohms

Question 2

to stimulate we use anode and cathode electrodes, but for recording we use?

Answer 2

Active (+) and Reference (-)

Question 3

Define gain

Answer 3

Gain- the amount that a differential amplifier amplifies the difference between the incoming voltages. Gain=output voltage/input voltage. (Vin= Reference-Active)

Question 4

Define Common mode rejection (CMR)

Answer 4

signals that are identically received by both inputs to the amplifier are rejected. Helps eliminate noise.

Question 5

Define common mode rejection ratio

Answer 5

how well a differential amplifier rejects common mode signals. 10,000:1 or 80 dB

Question 6

The input impedance should be?

Answer 6

Measured across the amplifier and > 10 MOhms

Question 7

Concepts of Fourier Spectrum and frequency domain.

Answer 7

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.

Question 8

What is the function of locut and hicut analog filters?

Answer 8

To eliminate unwanted high and low frequency. Decrease hicut=longer wave, increase locut= shorter wave, “lower means longer”

Question 9

Cutoff frequency

Answer 9

Signal is reduced by 3dB or 30 %

Question 10

60 hz notch filtering

Answer 10

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.

Question 11

Analog v. Digital filter

Answer 11

Digital Filters- produce no phase effects, reversible (smoothing)
Analog Filters- uses resistors and capacitors to filter the analog signal. Can create phase effects.

Question 12

Define Sampling rate

Answer 12

Number of data points collected/second

Question 13

Define Analog

Answer 13

Continuous sample in amplitude and time

Question 14

Define Digital

Answer 14

Discrete values (sample has specific amp and time)

Question 15

Define Bin

Answer 15

Interval time that sample is taken in.

Question 16

Define Dwell Time/Band width

Answer 16

Time between samples.

Bin Width= 1/ sampling frequency

Question 17

Define Nyquist Frequency

Answer 17

2 x the highest frequency of recorded signal

Aliasing- misrepresentation due to slow sample rate (below the nyquist)

Question 18

Define Horizontal Resolution

Answer 18

Want fast sampling frequency
Bin width- 20mcsec/data point
Sample Rate- 50 KHz

Question 19

Define Vertical Resolution

Answer 19

Number of Voltage values= 2^N N= number of bits

Must have 8 bits

Question 20

Define Range

Answer 20

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

Question 21

Understand the Signal averaging process, including the assumptions that make it work, and how it affects signal to noise ratio.

Answer 21

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

Question 22

Understands the process of artifact rejection and its application to averaging.

Answer 22

Sweeps that contain signals way outside do not get counted (completely erased) if intermittent

Question 23

Understands the concept of Display Gain, Scale and Sensitivity.

Answer 23

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)

Question 24

Understand the relationship between stimulus repetition rate and analysis period (sweep) and the factors that influence the choice of rep rate.

Answer 24

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)