ABEM Equipment Operation & Data Interpretation 2 — Questions and Answers
Question 1: What is the primary purpose of a notch filter set at 60 Hz in EMG/NCS equipment?
- Amplify the signal at 60 Hz
- Eliminate electrical interference from AC power lines (Correct answer)
- Increase the high-frequency bandwidth
- Reduce stimulus artifact duration
Correct answer: Eliminate electrical interference from AC power lines
A 60 Hz notch filter selectively attenuates electrical noise introduced by AC power line interference without significantly affecting the biological signal.
Question 2: When performing nerve conduction studies, a 'stimulus artifact' that obscures the early response is best reduced by:
- Increasing stimulus duration
- Rotating the stimulating electrode 90 degrees
- Reducing the distance between stimulating cathode and anode (Correct answer)
- Increasing gain on the amplifier
Correct answer: Reducing the distance between stimulating cathode and anode
Increasing the distance between cathode and anode reduces the voltage gradient at the recording electrodes, minimizing stimulus artifact.
Question 3: In needle EMG, the term 'insertional activity' refers to:
- Spontaneous discharges at rest after needle placement
- Electrical activity generated by mechanical displacement of muscle fibers during needle movement (Correct answer)
- Motor unit action potentials during voluntary contraction
- Artifact caused by patient movement
Correct answer: Electrical activity generated by mechanical displacement of muscle fibers during needle movement
Insertional activity is the brief burst of electrical potentials produced when the needle mechanically depolarizes muscle fibers during insertion or movement.
Question 4: The impedance of recording electrodes should ideally be kept below what value to ensure signal quality in electrodiagnostic studies?
- 50,000 ohms (50 kΩ)
- 500 ohms (0.5 kΩ)
- 5,000 ohms (5 kΩ) (Correct answer)
- 500,000 ohms (500 kΩ)
Correct answer: 5,000 ohms (5 kΩ)
Electrode impedance should be kept below 5 kΩ (with matched impedances between electrodes) to maximize signal-to-noise ratio and minimize artifact.
Question 5: A nerve conduction study shows a prolonged distal latency with normal conduction velocity in the proximal segment. This pattern is most consistent with:
- Axonal loss affecting the entire nerve
- Focal demyelination at or near the distal recording site (Correct answer)
- Neuromuscular junction disorder
- Technical error in proximal stimulation
Correct answer: Focal demyelination at or near the distal recording site
Focal demyelination at the distal segment slows conduction specifically there, prolonging distal latency while leaving proximal velocity intact.
Question 6: During F-wave studies, the minimum F-wave latency is used rather than the mean because:
- It is easier to measure on the screen
- It reflects the fastest-conducting motor axons and is most reproducible (Correct answer)
- It eliminates the need for multiple stimulations
- It correlates best with sensory nerve amplitude
Correct answer: It reflects the fastest-conducting motor axons and is most reproducible
The minimum F-wave latency reflects the fastest-conducting motor fibers and is the most reproducible and clinically meaningful value.
Question 7: When calibrating an EMG machine, sensitivity is expressed in:
- Milliseconds per division
- Microvolts per division (Correct answer)
- Hertz per division
- Milliamperes per division
Correct answer: Microvolts per division
Sensitivity (gain) on EMG equipment is expressed as microvolts (µV) or millivolts (mV) per division on the vertical axis of the display.
ABEM Equipment Operation & Data Interpretation 2
What is the primary purpose of a notch filter set at 60 Hz in EMG/NCS equipment?