ARDMS SPI Pulsed-Wave and CW Doppler 2

Question 1

What is the primary disadvantage of continuous-wave (CW) Doppler compared to pulsed-wave (PW) Doppler?

Accepted Answer

It has no range resolution and cannot localize the depth of flow

Answer

CW Doppler uses two separate crystals (one transmitting, one receiving continuously), so it cannot determine the depth of origin of Doppler signals — it samples all velocities along the entire beam path.

Question 2

In pulsed-wave Doppler, the sample volume (gate) is positioned within the vessel of interest. What determines the axial length of the sample volume?

Accepted Answer

The gate length (time duration of the listening window)

Answer

The axial length of the PW Doppler sample volume is determined by the gate length — the longer the listening window (in time), the larger the axial sample volume.

Question 3

A sonographer is scanning a patient and detects aliasing on PW Doppler. Which of the following actions would BEST eliminate aliasing without switching to CW Doppler?

Accepted Answer

Increase the baseline shift and/or increase the PRF

Answer

Aliasing occurs when the Doppler shift exceeds the Nyquist limit (½ PRF); increasing the PRF raises the Nyquist limit, and shifting the baseline allows display of higher unidirectional velocities.

Question 4

The Doppler equation states that the Doppler shift is directly proportional to which of the following?

Accepted Answer

The transmitted frequency, flow velocity, and cosine of the Doppler angle

Answer

The Doppler shift (Δf) = 2 × f₀ × v × cos θ / c, meaning it is directly proportional to the transmitted frequency, flow velocity, and the cosine of the angle between the beam and flow direction.

Question 5

When the Doppler angle approaches 90°, what happens to the measured Doppler shift?

Accepted Answer

It approaches zero, making velocity measurement unreliable

Answer

At 90°, cos 90° = 0, so the calculated Doppler shift approaches zero regardless of actual flow velocity, making angle correction and velocity measurement unreliable.

ARDMS SPI - ARDMS Sonography Principles and Instrumentation Practice Test

ARDMS SPI - ARDMS Sonography Principles and Instrumentation Practice Test

ARDMS SPI Pulsed-Wave and CW Doppler 2