2 module basic instrumentation

Module 2Basic Instrumentation For

IOM

NOTE: THE ENCLOSED INFORMATION IS A MERE SUPPLEMENT TO ALL OTHER PERTINENT INFORMATION FOUND IN JOURNAL ARTICLES, TEXTBOOKS AND OTHER PROFESSIONAL LITERATURE. THIS INFORMATION IS NOT INTENDED TO REPRESENT A COMPLETE SUMMARY OF ALL THE REQUIRED LEARNING FOR THE CNIM.

Neurocat CNIM Test PreparationModule 2 Basic InstrumentationSpring 2011

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TABLE OF CONTENTS

TABLE OF CONTENTS............................................................................................2

SECTION 1: CURRENT FLOW..............................................................................3

Fundamental of Electricity.............................................................................................3

Conductors................................................................................................................................3

Insulators..................................................................................................................................3

Terminology.............................................................................................................................3

LESSON 2: INSTRUMENTATION.......................................................................6

Differential Amplifier.........................................................................................................6Specifications.........................................................................................................................6Input Impedance...................................................................................................................6Common Mode Rejection..................................................................................................6Polarity......................................................................................................................................7Gain and Sensitivity.............................................................................................................7Filters........................................................................................................................................7Filter Slopes...........................................................................................................................8Period of a Waveform.........................................................................................................8Frequency................................................................................................................................8Digital Filter...........................................................................................................................8Notch (60Hz) Filter.............................................................................................................8Analog-to-Digital Conversion...........................................................................................9Sampling Rate........................................................................................................................9Dwell Time..............................................................................................................................9Aliasing...................................................................................................................................10Vertical Resolution.............................................................................................................10Signal-to-noise Ratio.........................................................................................................11Artifact Rejection................................................................................................................12Averager.................................................................................................................................12Simultaneous Averaging..................................................................................................12Multiple time bases...........................................................................................................12Epoch.......................................................................................................................................12Calibration.............................................................................................................................12Replications..........................................................................................................................12


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SECTION 1: CURRENT FLOW

Fundamental of Electricity

An understanding of the basic concepts of electricity is essential to appreciate the techniques compromising Clinical Neurophysiology. Electricity is the phenomenon of flow of electrical charge. Charge (Q) is a concept that evolved from empirical observation of electricity in nature and in experiments. Although charge can either be positive or negative, it is the flow of negative charge is the coulomb which represents the negative charge 6.35 x 1018 electrons. Because electricity represents a flow of charge, it must be directional. The direction of charge flow has been arbitrarily defined as flow from positive to negative. Current (I) is the amount of charge flow per time unit. An ampere (A) is the primary unit of current, defined as the flow of one coulomb of charge per second.

Electricity flows as an electrical current in a wire. This flow is made up of electrons which are subatomic particles. It is therefore necessary to understand some basic atomic structure.

An atom is made up of a nucleus which contains protons and neutrons. Electrons orbit this nucleus in so called shells. The shells or orbits do not actually exist, they represent different energy levels for the electrons.

An atom always has zero charge. This means that it must have the same number of protons as electrons. If an atom looses or gains one or more electrons it forms an ion

Conductors Conductors are those substances in which the outer electrons

(typically only one or two in each atom) can move freely from one atom to the next.

Current flows easily through conductors. Examples of conductors include: metals such as copper, iron, aluminum, platinum and water containing dissolved minerals.

The movement of electrons is “current” o Electrons flow from negative (-) to positive (+) o Conventional current flows from positive (+) to negative (-)

Insulators Insulators are substances in which all the electrons in the atoms of

the substance are tightly bound. The electrons do not easily move from one atom to the next. It is very difficult to get current to flow


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through insulators. Examples of insulators include: ceramics, rubber, plastic, and surprisingly, pure water

TerminologyVoltage

Refers to the amount of potential electrical energy between two charged points in space.

Basic unit of electromotive force (E) is the Volt (V)

Current Amount of charge flow per time unit Basic unit of current (I) is Ampere

Resistance Encountered when charge moves in matter Basic unit of resistance is ohm Resistors in series: R= R1 + R2 + R3 …. Resistors in parallel R = 1/ (1/R1 + 1/R2+ 1/R3…)

Power Delivering a specific amount of current at a specific voltage Basic unit of power (P) is the watt P = (E) x (I), P + E(sq)/R, P= I (sq)

Ohm’s Law Ohm's law is the main basic electrical law and defines the

resistance of a device to the flow of electrons. The principle by which voltage, current, and resistance are

related States: Voltage (V) is equal to current (I) flowing in the

circuit, multiplied by resistance (R) in the circuit V= (I) x R, or I = V/R, or V/I The letter E is sometimes used instead of V for voltage Most people can remember a picture easier than a

mathematical formula. By knowing any two values you can figure out the third.

Simply put your finger over the portion of the symbol you are trying to figure out

and you have your formula.

Electrode Impedance (Z)


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Represents the combined effects of resistance, capacitive reactance and

inductive reactance that occurs in AC circuits. Impedance for scalp electrode should be between 1,000 –

5,000 ohms Very low impedance (Less than 1,000) may short circuit the

amplifier input (e.g., sweat or salt bridges) Impedance of the stimulating electrode has a direct and

severe affect on the output to the nerve.

Note:Electrode resistance - opposition to direct current flowElectrode impedance - opposition to alternating current flow

Capacitance A capacity is defined as an electrical circuit element used to

store a charge temporarily, consisting in general of two metallic places

separated by a dielectric Capacitance is the ratio of charge to potential of an

electrically charged, isolated conductor The unit of capacitance is farad. Capacitors block direct current but pass alternating current

Inductance The property a circuit possesses that cause voltage to be

induced in the circuit when there is a variation in current flow Inductance opposes any change in current The unit of inductance is the Henry (H)

Current Leakage Defined as the low value electrical current that inherently

flows (leaks) from the energized electrical portions of an instrument to the metal

chassis. All electrically operated equipment has some leakage

current. For equipment where patients have direct contact, leakage

current must not exceed 100 μA


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Artifact

Defined as unwanted signal that contaminates recordings Four basic sources of artifact include:

1) Patient or unshielded electrodes can act as an antenna

2) Recording electrodes connected to other recording equipment act as conductors

3) The recording leads or cables connecting the patient with the recording equipment conduct magnetic field artifacts

4) Interference leaks into the amplifiers from the power lines

Keeping electrode impedances as low and evenly match as possible helps

eliminate in-phase artifacts Stimulus artifact is a specific type of artifact. It occurs early

in the recording and is caused by free electrons from the stimulus charge

reaching the recording electrodes. The standard for setting up any

stimulus/recording array is to place ground halfway between the stimulus and recording site.

The ground will draw off the electric charge before it reaches the recording site.

LESSON 2: INSTRUMENTATION

Differential Amplifier


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Specifications

Noise level of the amplifier must not exceed 2 uV rms with the inputs

connected to neutral and with a bandpass of 0.1 to 5000 Hz Meet specification in presence of a sustained 300 mV offset

applied differentially

Input Impedance

Electrical impedance of the amplifier input must be high compared with that of

the recording electrodes High input impedance insures against a loss of amplitude of

signals recorded The input impedance of the amplifiers should be 10 M ohm

or more

Common Mode Rejection

Differential amplification rejects signals of identical potentials, these potential changes are said to be “common mode”

The ability to reject common mode signals is called the common mode rejection ratio (CMMR)

Defined as the ratio of the amplification of the signals that are different in the two inputs of an amplifier, to the amplification of the signals that are the same in the two inputs.

CMRR for EP amplifiers should be 10,000 to 1, i.e., 80 dB or more

CMRR is facilitated by impeccable electrode application technique that insures that the 60 Hz is picked up at the same amplitude and phase in all electrodes

Page 36 of the Concise Handbook: Often the CMRR is given in decibel (dB). A number can be converted to decibels by first taking the logarithm in base 10 of the number and then multiplying by 20.

CMRRdb = 20 x log10(CMRR)

LOG (1000) = 3 multiplied by 20 = 60 dbLOG (10000) = 4 multiplied by 20 = 80 dbLOG (100000) = 5 multiplied by 20 = 100 dbLOG (1000000) = 6 multiplied by 20 = 120 db


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Polarity

There is no universally accepted polarity convention for EP recordings

Two polarity conventions exist for differential amplifiers

Either:1) A positive signal at input I produces an upward

deflection at the output and; A positive signal at input II causes a downward output deflection

Or2) A positive potential at input I causes a downward

deflection at the output and; A positive potential at input II produces an upward output deflection

The deflection (up or down) presentation of the waveform is dependent on the EP instrument. The polarity of the event is event/generator specific and cannot be changed

The term “active electrode” is usually used to indicate the electrode that is closer to the generator as compared to the “reference electrode” which would be farther away.

Gain and Sensitivity

Gain should be adjustable in steps of not more than 2.5 to 1 Gain and Sensitivity are terms which manufactures use for

similar functions. The key terms which will differentiate one from the other are as follows:

SENSITIVITY Is the number of micro-volts represented by a

specified distance (e.g., division) A larger number will result in smaller

waveforms (less sensitive) (e.g., 50 mV/div versus 20 mV/div)

GAIN Is the ratio of voltage or power out to the

voltage or power in A larger number will result in larger waveforms

FiltersNeurocat CNIM Test PreparationModule 2 Basic InstrumentationSpring 2011

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A filter is a circuit that is designed to pass a specific band of frequencies while attenuating (blocking) all signals outside this band. Filter networks may be either active or passive. Passive filters networks contain only resistors, inductors, and capacitors. Active filters employ amplifier circuits such as transistors or operational amplifiers plus resistors, inductors, and capacitors.

Band-pass filters pass only a band of frequencies while attenuating all frequencies out the band.

Low Frequency Filter (LLF) (High pass filter) Reduce the amplitude of slow waves without attenuating

faster waves Excessive low-frequency filtering will cause a peak or valley

to appear earlier, leading to possible falsely normal results

High Frequency Filter (HFF) (low pass filter) Reduce the amplitude of waves of high frequency and let

waves of low frequency pass without attenuation Excessive high-frequency filtering will delay (prolong) a peak

or valley leading to a possible falsely abnormal study.

Helpful tip: The bigger the number in (Hz) on the filter, the shorter the latency

Filter Slopes

Low Frequency Filters Roll-off slopes should not exceed 12 dB octave If a frequency is reduced by 50%, it is said to have change by

one octave

High-Frequency Filters Roll-off slopes should not exceed 24 dB octave (HFF) The time required for a sudden input voltage to rise to 63% of

its peak voltage equals: T=R, C in an RC filter

With each reduction of the input frequency by one octave, the output amplitude typically will be reduced by 50%. This is called the “roll-off”

LLF is usually a passive filter made of a capacitor in series and resister in parallel to the signal path. The cutoff is usually defined as 3 –dB point (or the frequency at which the signal at the filter output is reduced to 3 dB or 30 percent)

Time constant may be determined by measure the time interval between the onset of the sustained calibration pulse and the point at which its amplitude has dropped to 37%


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Period of a Waveform

The period of a waveform is the time required for completing one full cycle. It is measured in seconds

Frequency

The frequency of a waveform is the number of cycles that is completed each second. It is measured in Hertz (Hz)

Digital Filter

Operates on digitized responses to eliminate components of low or high frequency with very high cutoffs and without phase shift

Digital filtering causes no temporal distortion of EP waveforms

Notch (60Hz) Filter

Most common cause is unequal electrode impedance Greatly reduce waves of frequencies in a very narrow band

concentrated around 60 Hz. Affects the most common artifact from power-line

interference of 60 Hz May distort EP waveforms

Analog-to-Digital Conversion

Continuous voltage changes of the data are converted into a sequence of numbers (digital format)

This display is displayed as a sequence of illuminated dots The degree of similarity between the analog signal and its

digital counterpart is dependent of each of the items listed below.

Several Important Rules exist that must be followed when digitally sampling physiologic signals:

1. Amplifiers must have sufficient sensitivity and CMRR to detect and amplify the signal

2. The A-D converters must have a liner response over the dynamic range of the signal

3. The A-D converters must have an adequate sampling rate and resolution to faithfully reproduce the signal.

Sampling Rate

Sampling rate is defined as the number of points per second that a computer is using to digitize the response on the horizontal axis


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Sample rate and dwell time define the horizontal resolution or time (frequency) resolution.

Horizontal Resolution is dependent upon1) Analysis time required to do the test2) Number of points selected3) Horizontal resolution of 20 μsec/address/channel is

preferred Sampling rate (in Hz) is calculated as:

# sampling pointsanalysis time (sec)

Dwell Time

Dwell time is the inter-sample interval or the space between each point.

Dwell time is calculated as follows:

analysis time# of points

Most instruments allow the user to define sampling rate or number of sampling points. Dwell time will change with an edit of either of these options.


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Nyquist Frequency Defined as: the sampling frequency should be at least twice

as fast as the highest frequency being recorded. If not, aliasing could occur.

For example, to duplicate the standard EEG frequency range of 0.1 Hz to 70 Hz, each channel must be sampled digitally at 140 Hz

Example:What can you say about a system trying to resolve a 40 μS sine wave with a sampling rate of 40 kHz?

1. No aliasing will occur2. Aliasing will occur3. Aliasing may or may not occur depending on the bits4. Aliasing may or may not occur depending on the Nyquist

frequency

Nyquist Frequency: Defined as: the sampling frequency should be at least twice as fast as the fastest frequency being recorded.

Therefore, at a sampling rate of 40 kHz, the fastest waveform that can be

resolved is 20 kHz. At 40 us (0.04 ms) sine wave has a frequency 1000 ms/.04 =

25000 Hz, or 25 kHz.

Aliasing WILL occur because the sine wave of 25 kHz is GREATER than the maximum frequency of the waveform that can be resolved which is 20 kHz.

Aliasing

Aliasing is the computer induced artifact which is present when the sampling rate is too slow Aliasing may appear as corruption in both frequency and amplitude presentation

Vertical Resolution

Size of A/D converter Sizes range for 4-12 bit Most resources state that the most common is 8 bit, however with the advent of the digital EEG, the most common is now an 11-16 bit converter 8 bit allows for 256 unique voltage values (+/-)


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Excessive amplification will result in clipping of the waveform and corrupt amplitude values

Insufficient amplification results in waveform flattening and corrupt amplitude values

Number of trials, sweeps, epochs Amplitude resolution is improved by increasing the number of trials

(improving signal to noise ratio) Vertical resolution is controlled by the number of bits in the A-D converter. The larger the # of bits the larger the unique voltage values that can be stored the greater the vertical resolution. The +/- voltage range associated with the A to D converter, unique points in that range and modality being recorded.


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Signal-to-noise Ratio

Defined as the ratio of the amplitude of the stimulus locked components (signal) to the amplitude of the unrelated components (noise)

This ratio improved with the number of responses averaged. The noise decreases by the square root of the number of

averages.

Typical CNIM Question: If an evoked response of 5 uV occurs in EEG activity of 20 uV, how many responses need to be average to obtain a signal to noise ratio of 2:1?

1. 82. 163. 644. 128

IMPORTANT: You must know that the signal-to-noise ratio will improve with SQUARE ROOT of the number of trials.

There are different ways of answering this but here is one:

Signal-to-Noise = SNR

SNRnew = SNRold multiplied by SQUARE ROOT (Number of trials)

From the question above

SNRnew = 2:1SNRold = 5:20SQUARE ROOT (Number of trials) = X

Plug these values into the equation:

2/1=5/20 multiplied by X

Solve for X, using basic algebra

X = (2 x 20)/5

X = 8

8 represents the SQUARE ROOT of the number of trials so you must SQUARE X to determine the number of trials.

Therefore, 8 x 8 = 64.


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The answer is 64 trials.

Artifact Rejection

Characteristic of EP instruments whereby artifact-contaminated trials can be excluded from the average

Achieved by rejecting those trials that exceed the limits of the A-D converter or some

adjustable percentage thereof. Most commonly set to 90-98% of the dynamic range of the A-D Setting a percentage of A-D converter is one means for artifact rejection.

The other is to have an addition uV detection level that will eliminate individual trials.

Averager

Time resolution should be 20 us/data point or less Amplitude resolution of the A-D converter should be at least 8 bits 500 address of memory should be available for each channel Allow for averaging of at least 4000 trials

Simultaneous Averaging

Averaging multiple modalities at the same time It is usually interlaced and asynchronous. For example, averaging left

upper SSEP, right upper SSEP, left lower SSEP and right lower SSEP Alternatively, running synchronous. For example, both upper and/or both

lowers stimulated together.

Multiple time bases

Able to display and/or record the same modality in different time bases. For example,

BAERs using 1 msec and 2 msec on the same data.

Epoch

Is the total amount of time, starting either pre-stimulus or at the start of the stimulus, to the

end of the data collection

Calibration

Injecting into the input jacks of each channel rectangular pulses of appropriate amplitude,

usually 0.5-100 uV, time-locked to the onset of the sweep. Calibration pulses must be amplified and average and their amplitude

measured in conditions


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identical to those to be employed for the recording of the evoked potential under study

Replications

Replication of the response is imperative to demonstrate that clinically evoked responses are

consistently repeatable and therefore are of neural and not artifact in origin.

Replication is demonstrated by the consistency of latency and amplitude measure of evoked

potential components recorded in successive averages. Latency replication within 1.0 % of

the total sweep time and amplitude replication within 15% of the peak-to-peak amplitude can

usually be achieved. Poor replication may be caused by:

▫ unusually low (but not necessarily abnormal) amplitude responses▫ excessive artifact▫ insufficient number of responses in the average

CNIM Preparation – Basic Instrumentation Questions & Answers

1. A differential amplifier records: a. Only the first two inputsb. The second half of the two inputsc. The power of the sum of the two inputsd. The difference between the two inputs

Nuwer (1983) page 15 – ref # 11

1. To accurately represent the amplitude of an EP waveform a match must be made between the:

a. Signal size and the vertical capacity of the digitizerb. High-frequency noise and smoothing operation of the instrumentc. Dwell time and sampling rate d. Horizontal resolution and signal size

Misulis (1994) page 32 – ref # 9

1. Due to a smaller surface area, sub-dermal needle electrodes will have an impedance that is:

a. Lower than disk electrodesb. Increased with improper insertionc. Improved by cleansing the skin with an abrasive geld. Higher that surface electrodes

Tyner (1983) page 130 -- ref # 15

1. The difference between the voltage in input 1 and input 2 will make the display


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of the amplifier move: a. Ina sinusoidal patternb. Upc. Either up or downd. Down


1. In order to stimulate both tibial nerves asynchronously, you need: a. To delay the first stimulatorb. To delay the second stimulatorc. A positive trace delayd. A negative trace delay

Nuwer (1986) pages 30 and 31 – ref # 11

1. The input impedance of a differential amplifier must be at least: a. <5 K ohmsb. 10 megohmsc. 100 megohmsd. <10 megohms

AEEGS (1994) pages 42 – ref # 11. An EP recording system should allow averaging of:

a. 600 trials or more b. no more than 500 trialsc. a maximum of 2000 trialsd. at least 4000 trials

AEEGS (1994) page 42 – ref # 1

1. “Signal-to-noise ratio” relates to which of the following? a. The amplitude of the evoked response components to the amplitude of the unrelated components.b. The ability of the instrument to resolve data and noise vertically.c. Two inputs of a differential amplifier with like negativityd. Sensitivity scaling


1. “Electrode impedance” is defined as opposition to: a. direct current flowb. alternating current flowc. different current flowd. 60 Hz artifact


1. A constant voltage stimulator: a. Varies the current in order to maintain a preset voltage levelb. Maintains a constant voltage of 100 voltsc. Varies the output in order to maintain a preset current level


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d. Maintains a current level of 10 mALoftus (1994) page 158 – ref # 8

1. The sound stimulus intensity at the tympanic membrane depends on the: a. Acoustic coupling between the sound stimulus generator and the earb. Relation between SPL (dB) and the inverse peak equivalent SPL (dB)c. Relation between SPL (dB) and peak equivalent SPL (dB)d. Patient ‘s hearing threshold (dB)

Misulis (1994), page 119

1. For the intraoperative recording of EEG the impedance of a scalp electrode should range from:

a. 250 to 500 ohmsb. 500 to 1000 ohmsc. 1000 to 5000 ohmsd. 5000 to 10,000 ohms


1. The use of the 60 Hz notch filter is discouraged while recording because it can: a. Produce a risk to the patientb. Produce ringing activity that can contaminate the appearance of the responsec. Cause the recording electrodes to form a salt bridged. Filter slow activity distorting the response

AEEGS (1994) PAGE 43 – REF # 1

1. The gain of an amplifier set to give an output signal of 1 volt for an input signal of 10 uV is: a. 100b. 1,000c. 10,000d. 100,000


1. The following are examples of good insulating materials, inhibiting current flow; a. silicon and germaniumb. silver and copperc. glass and rubberd. gold and platinum

Tyner (1983) page 35 – ref # 15

26758. In selecting the horizontal parameters of analysis the a. Sampling rate should be at least two times greater than the highest frequency in the signalb. Sampling rate should be the equivalent of the highest frequency in the signalc. Analysis period should be at least twice the Nyquist frequency


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d. Analysis period should approach the Nyquist frequencyMisulis (1994) page 30 – ref # 9

17. The phenomenon called “aliasing” a. may be avoided by proper placement of the ground and stimulating electrodes.b. Is common during intraoperative recording of evoked potentialsc. Refers to an erroneous representation of an analog signal by digital valuesd. Occurs when the analysis period is more than twice the Nyquist Frequency

Misulis (1994) page 30—ref # 9

18. Brain activity recorded directly from the cortex (ECoG) is very high in amplitude and usually requires sensitivities in the range of:

a. 10 to 50 mV/mmb. 40 to 100 mV/mmc. 100 to 150 mV/mmd. 200 to 300 mV/mm

ASET (1998) page 210 – ref # 5

19. The assumption that responses of excessive amplitude are likely to contain artifact forms the basis for:

a. Digital filteringb. Dwell timec. Artifact rejectiond. Digital averaging


20. A capacitor is an electronic device used to: a. Store electrical energyb. Stop current flow when some critical power level is exceededc. Enhance current flow d. Measure electrode impedance at the scalp

Tyner (1983) page 44 -- ref # 15

21. “Pre-stimulus triggering” a. presents a positive signal to the averager prior to initiating the displayb. includes a period of recording before the stimulusc. eliminates the problems associated with recording the stimulus artifactd. delays the synchronizing pulse to the computer


22. The horizontal resolution of an evoked potential system: a. Should be 20 microseconds per data point or lessb. Has no effect on the aliasing properties of the instrumentc. Should be greater than 30 milliseconds per data point


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d. Is one half the Nyquist frequencyAEEGS (1994) page 42 – ref # 1

23. A unit of resistance is symbolized by: a. Ab. mc. Wd. E

Tyner (1983 page 35 – ref # 15

24. SSEP recordings typically require a wide bandpass of: a. .5 Hz to 200 Hzb. 1 Hz to 1,000 Hzc. 5 Hz to 3,000 Hz d. 5 Hz to 5,000 Hz


1. Given an electrical circuit with a resistance of 1,000 ohms and a voltage of 10 volts, the current flow will be:

a. .01 Ab. .10 ohmsc. 10 Ad. 100 volts

Tyner (1983) page 35 to 37 – ref # 15

26. The common mode rejection ratio of amplifiers used for EP recording should be at least:a. 100:1b. 1,000:1c. 10,000:1d. 100,000:1


27. Spectral edge is a function of: a. Beta and alpha vs. timeb. Amplitude and latency vs. timec. Power and frequency vs. timed. Zero crossing intervals

ASET (1996b) page 110 – ref # 4

57. With a sampling rate of 10 kHz the shortest sine wave resolved would be:a. 2 msecb. .2 msecc. .4 msec


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d. .02 msecMisulis (1994) page 30 – ref # 9

58. If you have a signal to noise ratio of 1:2 averaging 64 responses will: a. reduce the noise by 50%b. Not change the ratioc. Improve the ratio to 8:1d. Improve the ratio to 4:1


59. A Condensation click:a. delivers loudest sounds to the tympanic membraneb. cause the tympanic membrane to move out ward c. causes the headphone diaphragm to displace toward the tympanic membraned. causes the headphone diaphragm to move away from the tympanic membrane

Russell (1995) page 141 – ref-- # 14

60. Reduction of the high frequency filter:a. Has no effect on evoked potential latencyb. Has an unpredictable effect on evoked potential latencyc. Increases evoked potential latencyd. Decreases evoked potential latency


61. The duration of a monophasic rectangular pulse used for somatosensory stimulation should be:a. 0.05 msb. 0.2msc. 0.5msd. 1 ms


62. The sensitivity setting on a amplifier set to produce a vertical deflection of 1 cm with an input of 10 mV is:

a. 1 mV/mmb. 1mV/cmc. 10mV/mmd. 20mV/cm


63. A rarefaction click occurs when the:a. Initial movement of a transducer diaphragm is towards the tympanic membraneb. Initial movement of a transducer diaphragm is away from


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the tympanic membranec. Movement of a transducer diaphragm alternates in polarity relative to the tympanic membrane every second traila. Movement of a transducer diaphragm alternates in polarity relative to the tympanic membrane on a random basis

Misulis (1994) page 122 –ref # 9

64. All of the following are true of magnetic stimulation except:a. An electrical stimulator is required to pace the stimulusb. The stimulation is not perceived as painfulc. Pulses of current are delivered through a coil of wired. The magnetic field created causes movement in cortical neurons.


65. An after-discharge can occur on the cortical EEG recording following:a. A seizure recorded in the operating roomb. Electrical stimulation of the exposed cortexc. The introduction of 60 Hz artifactd. Electrocautery.

Russell (1995) page 200 -- ref #1466. To minimize pain from stimulation during the recording of SSEPs, the contact impedance should be:

a. Less than 50 kiloOhms b. More than 10,000 ohmsc. Less than 5,000 ohmsd. Less than 10 megohms


67. The recommended filter settings for the facial nerve CMAP are:a. 1-1.5 kHzb. 1-15 kHzc. 10 –1.5 kHzd. 10-15 kHz

AEEGS (1994) page 841 – ref # 1

68. Spinal cord evoked potentials are best recorded using a low frequency filter setting of 100 Hz. This setting is preferred because relative to cortical somatosensory evoked potentials spinal cord potentials are:

a. of relatively short durationb. less affected by changes in anesthesiac. subject to 60 Hz interferenced. an extremely low voltage response

EEGS (1994) page 83 ref # 1

69. In the operating room, the stimulus intensity for activating a sensory nerve:a. should be set at double the sensory thresholdb. should be set for two to three times the motor threshold


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c. does not have an established boundaryd. is set slightly above motor threshold


70. The suggested rate of stimulation for intraoperative posterior tibial nerve evoked potential monitoring is:

a. 30 to 40 per secondb. 20 to 30 per secondc. 10 to 20 per secondd. 2 to 10 per second


71. The effect of pharmacological or surgical manipulations can be mimicked by the inappropriate manipulation of:

a. The stimulus rateb. The stimulus intensityc. Filter settings d. The group electrode

AEEGS (1994) pages 79 and 83 – ref # 1

72. Direct focal electrical stimulation of a peripheral nerve lesion willa. Define epileptiform activity generated in the lesion b. Identify begin masses versus malignant tumor massesc. Be of no valued. More precisely localize the distribution of intact conducting nerve fibers

Loftus (1994) page 279 – ref #8

73. For stimulation in spinal cord motor evoked potential (MEP) studies, the anode should be placed:

a. Rostral to the cathode b. Caudal to the cathode c. Medial to the cathoded. Lateral to the cathode

Russell (1995) page 165 – ref #14

74 . When monitoring Somatosensory evoked potentials during a critical moment in an intraoperative study, changing the setting of the high-frequency filter:

a. Will be of limited consequence to the outcome of the study b. May help isolate a true signal from background noise c. May increase the number of single trial events required to resolve the evoked response d. May lead to a false interpretation of the data


74. A stimulus pulse width that would tend to excite a larger population of motor fibers


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than sensory fibers is: a. 0.05 msb. 0.2 ms c. 0.5 ms d. 1 ms

75. When using constant voltage for facial nerve stimulation and the nerve becomes bathed in CSF what will occur after the area is suctioned?

a. The output voltage will vary to maintain a preset current levelb. The current flow will vary in order to maintain the present voltage level c. No change will occur d. The stimulator will stop

Kartush (1992) page 104—ref # 7

76. Chassis leakage for evoked potential equipment used in the operating room should be less than:

a. 1 micro ampb. 10 milliampsc. 10 micro ampsd. 100 micro amps

AEEGS (1994) page 43 – ref # 177. The type of artifact most likely associated with blood warming equipment is:

a. Baseline awayb. 60Hz c. popping electrodesd. increased stimulus artifact

ASET (1996a) page 103 – ref # 3

78. The purpose of isolated amplifier inputs is to: a. Allow only the high voltage biological signs to passb. Restrict current flow to the instrumentc. Restrict current flow to ground at 20 uAd. Prevent a flow of stray currents through connecting lines to the patient

AEEGS (1994) page 78 – ref # 1 Tyner (1983) page 77 – ref # 15

79. Common sources of nonphysiologic artifact in the operating room include:a. Oxygenation, ventilation, and body temperatureb. Operating microscope, x-ray view boxes and heating devicesc. Movement in the room VCR monitors and surgical instrumentsd. The surgeon anesthesiologist and neurophysiologist

Russell (1995) page 243 – ref # 14

80. Although the use of electrical cautery can obliterate EP waveforms intraoperative monitoring should be continued:

a. Because the average will store the reliable waveforms b. By averaging the saturated waveforms


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c. By monitoring the raw (unaveraged) datad. Whenever the audible sound of the cautery is present

ASET (1996a) page 60 – ref # 3

81. Stimulus artifact during SSEPs can be decreased by:a. Keeping the instrument away from florescent lights and video monitorsb. Using enough muscle relaxantc. Separating stimulating cable from cable of other equipmentd. Lowering the impedance of ground electrodes

ASET (1996a) page 103 – ref # 3

82. According to current OSHA standards needle electrodes should:a. Be reused whenever possibleb. Not be soaked in a sodium hypochlorite solutionc. Be recapped before discardingd. Not be handled with tongs or forceps while cleaning

ASET 91995) page 164 – ref # 2

83. A term used to describe very low currents that may be lethal to patients with indwelling devices is:

a. Macroshockb. Ground loop c. Short circuitd. Microshock

Tyner (1983) page 76 – ref # 15

84. A recommendation to minimize stimulus artifact while recording BAEPs intraoperatively is to: a. Use alternating clicksb. Use larger sized headphones c. Use rarefaction clicksd. Decrease the impedance of your stimulating electrodes


85. To reduce artifact from electrode wire movement during surgery it is best toa. Use long wire and tuck them under the patientb. Braid the wiresc. Loop the wires under the patient headd. Use only paste and gold disc electrodes

ASET 91996a) page 51-- Ref # 3

86. Electrical hazards that exist for patients attached to medical equipment include all of the following except:

a. Ground faults Neurocat CNIM Test PreparationModule 2 Basic InstrumentationSpring 2011

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b. Leakage currentc. Needle sticksd. Indwelling electrodes

Tyner (1983) page 81 – ref # 15

87. An example of nonphysiologic artifact would be: a. High levels of muscle tensionb. Electrical interferencec. The ECG signald. Slow signal due to perspiration

ASET (1996a) page 102 –ref # 3

88. Electrode lead wires used in the operating room suite must be converted to safety connectors (female electrodes) by:

a. June, 1999b. May, 2000c. January, 1997d. January, 2005

ASET (1998) page 211 – ref # 5

89. A “ground loop” is created when: a. Two separate devices are attached to the same patient and have two separate grounding connections

b. Two recording electrodes are connected to two separate input box of the same instrumentc. The patient is grounded by the large electrocautery ground that resembles a loopd. Separate equipment attached to the same patient have current-limiting grounds

Russell (1995) page 60 – ref # 3

90. One function of the circuitry in an isolated input board is to protect the patient from electrical shock by limiting the current flow to at least:

a. 100 uAb. 20uAc. 60 uAd. 10uA

Tyner (1983) pages 77- ref #15

91. A grounding device must be available so that under normal conditions no voltage greater than ______________ is measured across an impedance of 1000 ohms:

a. 60 mV ms at 50 Hzb. 20 mV ms at 60 Hzc. 50 mV ms at 60 Hzd. 10 mV ms at 50 Hz


92. If the monitoring instrument develops an inability to average, steps to take would include all of the Neurocat CNIM Test PreparationModule 2 Basic InstrumentationSpring 2011

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following except:a. check electrode impedanceb. check that all cable are round separatelyc. insure that the stimulus rate is not a multiple of the interference frequencyd. consult with the anesthesiologist regard anesthesia change

ASET (1996a) page 106 – ref # 3

93. Both SSEP and BAEP waveforms can be affected by structural manipulation using: a. Retractorsb. grounding padsc. suctiond. blood pressure transducers

ASET (1996a) page 220 ref # 3 ASET (1996b) page 101 ref # 4

94. The term “broadband click “ refers to a: a. Peak acoustic power of 2-4 kHz b. Short peak acoustic power of 1-2 kHzc. Broad peak acoustic power of 1-5 kHzd. A peak acoustic power of 500Hz to 2kHz


95. Which of the following is not related to Ohm’s law?a. Electromotive force b. Impedance c. Voltage d. Phase e. Current

Ibid, page 5

96. Ohm’s law is: a. E=IR b. I-ER c. R=Ei d. 2I=E/Z e. Z+EI

Ibid, page 5

97. Input impedance should:a. be very high b. be very low c. Equal the common mode rejection ratio d. Affect low frequency activity e. Increase signal distortion

Kiloh, Mccomas and Osselton, Clinical Electroencephalography, Third Edition, Butterworths, 1972 page 36


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98. Gain is:a. The ratio of output signal to input signal b. The same as sensitivity c. Always less than 100:1 e. Expressed in dBf. Expressed in microvolts

Niedermeyer, E, and Lopes da Silva F Electroencephalography, Urban & schwarzenber, 1982, page 53.

99. In a differential amplifier, the common mode rejection of in phase signals is typically:a. 100:1 b. 500:1 c. 5:1 d. 10,000:1 e. 10:1

Ibid, page 59

100. Common mode rejection is:a. The ability of an amplifier to cancel out ECG artifact b. The characteristic of an amplifier that rejects external interference c. The same as input impedance d. Controlled by the 60 cycle notch filter e. Same as sensitivity

Ibid, page 58

101. The ratio of input voltage to output pen deflection is:a. sensitivity b. input impedance c. gain d. common mode rejection e. filter

Niedermeyer E, and Lopes da Silva F Electroencephalography, Urban & Schwarzenberg, 1982 page 53

102. In a differential amplifier, if input one received a voltage of 65 uV and input two a voltages of –30 uV, the output voltage seen would be _________uV and the pen would move ___________>:

a. 35 uV, upward b. 95 uV, downward c. –95 uV upward d. –35 uV downward


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e. 65 uV, upward Clenney S., and Johnson, S Back to Basics, Beckman instruments, Inc., 1983 page 86 and 87.

103. Which of the following is attenuated by time constant of .03 seconds?a. .10 Hz b. 15 Hz c. 25 Hz d. 3 Hz e. 60 Hz

Ibid, page 97

104. Which of the following is most attenuated by high frequency filter setting of 35Hz?a. 10 Hz b. 25 Hz c. 15 Hz d. 35 Hz e. 45 Hz

Ibid, page 48

105. Which of the following is attenuated by a high pass filter of 5Hz: a. 1 Hz b. 10 Hz c. 15 Hz d. 20 Hz. e. 25 Hz

Ibid page 101

106. The accepted limit allowed for leakage current from chassis of an evoked potential machine is:

a. 1 amp b. 10 milliamps c. 100 microamps d. 100 amps e. none is allowed

American Electroencephalographic Society, Guidelines for Clinical Evoked Potential Studies, J. Clin Neurophysiol 1:3-53, 1984 page 8

107. The most practical method to assure the integrity of an average is to demonstrate_____________ of independently collected averages:

a. Polarityb. Raw data c. Latencyd. Replication


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e. AmplitudeIbid page 9

108. Which of the following recording parameters can affect waveform morphology, latency and amplitude of evoked potentials:

a. High pass filters b. Low pass filters c. 60 Hz filterd. notch filtere. all of these

Ibid page 9

109. Signal averaging tends to increase “time-locked” events while random activity tends to zero. This is known as:

a. Signal to noise ratiob. A/D conversionc. Band –passd. Noise to noise ratioe. Signal to signal ratio

American Journal of EEG Technology, Book (Evoked Responses, 2 volumes), selected reprints, ASET Executive Office Vol. 1, page 14

110. A signal averager should have horizontal resolution of:a. 5 sb. 5 usc. 50usd. 50mse. 10us

American Electroencephalographic Society, Guidelines for Clinical Evoked Potentials, J. Clin Neurophysiol 1:3-53 page 8 Grass Ellen R. and Johnson, Edmund, Evoked Reponses Signal Averaging, Grass Instrument Co., page 14 & 15

111. Among the measurement taken from an evoked potential waveform the most clinically useful is:

a. Amplitudeb. Latencyc. Morphologyd. Interpeak latencye. B and d

Chiappa, K., Evoked Potentials in Clinical Medicine, Raven Press, 1983 page 18-21

112. The square root of the arithmetic average of the squares of the deviation from the mean is known as:

a. Meanb. Medianc. Mode


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d. Standard deviatione. Tolerance limit

Dictionary; Intro. to Evoked Potential Instrumentation, Nicolet Instrument Corporation, 1979

113. It is acceptable to use published normative date from another center for the analysis of evoked potentials when:

a. Stimulus, recording and other conditions are compatibleb. The other center’s normal values are closely matched to your select (at least 20)

normal subjectsc. Any published data is acceptabled. No published data is acceptablee. A and b only

American Electroencephalographic Society, Guideline for Clinician Evoked Potential Studies, J. Clin Neurophysiol 1:3-53 1984, page 11

114. Which of the following filter bandwidths will affect the latency and/ or amplitude of the brainstem auditory evoked potential?

a. 100-3kb. 100-10kc. 100-1kd. 30-3k

115. What affect does increasing stimulus rate have on the BAEP?a. Latencies are prolongedb. Amplitudes of waves I, II and III are attenuatedc. Amplitudes of wave Vi is attenuatedd. All of the abovee. A & b only

American Journal of EEG Technology, Book IV (evoked Response, 2 volumes) selected reprints, ASET Executive Office

116. Noise masking:a. To prevent bone conduction of the stimulus to the other ear not being testedb. A white noise, usually about 60 dB SPL (30 db NHL)c. Delivered to the contralateral (non-stimulated) eard. Should be done routinelye. All of the above

American Electroencephalographic Society, Guidelines for Clinical Evoked Potential Studies, J. Clin Neurophysiol 1:3 –53, 1984

117. Stimulus intensity should be adjusted to:a. 10mAb. 20mAc. produce pain then reduce 3mAd. sensation levele. produce a minimal movement at the joint involved


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Chiappa K., Evoked Potentials in Clinical Medicine Raven Press 1983 pg. 222

118. The optimal filter bandpass settings for recording PREPs is:a. 10-50b. 1-200c. 1-50d. 10-200e. 100-3,000

American Electroencephalographic Society Guidelines for Clinical Evoked Potential Studies J. Clin Neurophysiol 1:3-53, 1984 pg 24

119. The optimal filter settings for recording a somatosensory evoked potential of the upper extremity is:

a. 5-1000b. 150-3000c. 1-200d. 5-500e. 20-3000

Ibid page 42

120. Artifact rejection is designed to:a. Limit unwanted signals from entering the averageb. Reject voltages exceeding the sensitivity settingc. Improve the quality of the averaged. Count all average within amplitude boundaries selectede. All of these

Spehlmann, Ranier, Evoked Potential Primer, Butterworth Publishers, 1985 pages 47-48

121. When recording Evoked Potentials the phase shift caused by high and low frequency filter affects?

a. Latencyb. Amplitudec. Latency and amplitude equallyd. Time locking e. None of the above

Tyner, Knot and Mayers Fundamentals of EEG Technology Vol I, Raven Press 1983

122. 60 HZ filters cause a change of latency by a:a. phase shiftb. decrease in amplitude c. frequency of wavesd. frequency response curvee. ringing effectIbid.


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123. The number of grounds placed on the patient is only important when recording:a. Somatosensory evoked potentialsb. Visual evoked potentialsc. Auditory evoked potentialsd. Dermatones e. All of the aboveIbid.

124. The use of extension cords is discouraged because:a. Increased leakage currentb. Decrease in power supply to the machinec. The ground may not be intactd. Patients can trip over theme. A and C

Ibid.


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2 module basic instrumentation

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