ARDMS SPI - ARDMS Sonography Principles and Instrumentation Pulsed-Wave and CW Doppler Questions and Answers

Question 1

Which of the following is a primary advantage of Continuous-Wave (CW) Doppler over Pulsed-Wave (PW) Doppler?

Accepted Answer

It is not limited by aliasing at high velocities.

Answer

Continuous-Wave (CW) Doppler continuously transmits and receives ultrasound, so it does not have a sampling rate (PRF) that limits velocity measurement. This allows it to accurately measure very high velocities without the aliasing artifact that affects Pulsed-Wave (PW) Doppler.

Question 2

A sonographer observes that the spectral waveform on a Pulsed-Wave Doppler display appears to "wrap around" from the top of the scale to the bottom. This artifact is known as:

Accepted Answer

Aliasing

Answer

Aliasing occurs in PW Doppler when the measured Doppler shift exceeds the Nyquist limit (half the PRF). The system cannot sample the signal fast enough, causing the highest velocities to be incorrectly displayed on the opposite side of the baseline.

Question 3

A sonographer is performing a PW Doppler examination and notes significant aliasing. Which of the following adjustments is LEAST likely to correct this artifact?

Accepted Answer

Increasing the overall Doppler gain.

Answer

Increasing the Doppler gain amplifies the entire signal, including the aliased components, making the display brighter but does not correct the aliasing itself. Increasing the PRF raises the Nyquist limit, shifting the baseline provides more room for the waveform, and using a lower frequency transducer reduces the Doppler shift for a given velocity; all are valid methods to reduce or eliminate aliasing.

Question 4

Which of the following statements accurately describes a key characteristic of Continuous-Wave (CW) Doppler?

Accepted Answer

It cannot determine the exact depth from which a velocity signal originates.

Answer

Because a CW Doppler system transmits and receives sound continuously along the entire beam, it detects all velocities in its path. It cannot isolate a specific depth, a characteristic known as range ambiguity.

Question 5

A Pulsed-Wave Doppler system is operating with a Pulse Repetition Frequency (PRF) of 12 kHz. What is the maximum Doppler shift that can be displayed without aliasing?

Accepted Answer

6 kHz

Answer

The Nyquist limit states that the highest Doppler frequency that can be measured without aliasing is one-half of the Pulse Repetition Frequency (PRF). Therefore, with a PRF of 12 kHz, the Nyquist limit is 6 kHz (12,000 Hz / 2).

ARDMS SPI - ARDMS Sonography Principles and Instrumentation Practice Test

ARDMS SPI - ARDMS Sonography Principles and Instrumentation Practice Test

ARDMS SPI - ARDMS Sonography Principles and Instrumentation Pulsed-Wave and CW Doppler Questions and Answers