Free Practice Questions for ARDMS SPI Exam

Color flow Doppler imaging displays the mean Doppler frequency shift, which represents the average velocity of blood flow within a sample volume. The ultrasound system uses autocorrelation to process Doppler signals and compute the mean frequency shift. This provides a color-coded map of blood flow velocities, allowing for visualization of flow direction and speed. The mean Doppler frequency is displayed as different colors, with each color representing a range of velocities.

Comprehensive and Detailed Explanation From Exact Extract:

Aliasing occurs when the Doppler shift exceeds the Nyquist limit, which is directly tied to pulse repetition frequency (PRF), represented on the machine as Doppler scale. A Doppler scale set too low reduces the Nyquist limit, making aliasing more likely.

According to sonography instrumentation reference:

“Aliasing occurs when Doppler scale (PRF) is set too low relative to the measured velocities, causing signal wrap-around.”

Therefore, the correct answer is B: Doppler scale too low.

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Comprehensive and Detailed Explanation From Exact Extract:

Power Doppler detects the strength (amplitude) of returning Doppler signals, which reflects the presence of flow regardless of direction or velocity. It is more sensitive to low-velocity flow and is less angle-dependent than conventional color Doppler.

Principles and Instrumentation state:

"Power Doppler displays the amplitude of Doppler shifts, representing the presence of flow. It does not display direction or velocity."

Laminar flow (A) and velocity (C) are not specifically measured by power Doppler.

Viscosity (D) cannot be assessed by Doppler ultrasound.

Therefore, the correct answer is B: Presence of flow.

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Comprehensive and Detailed Explanation From Exact Extract:

Higher frequency transducers provide better axial resolution due to their shorter wavelengths and spatial pulse lengths. This allows finer detail when imaging superficial structures where penetration is not a concern.

According to sonography instrumentation reference:

“Higher frequencies result in shorter pulse lengths, improving axial resolution and making them ideal for superficial imaging.”

Therefore, the correct answer is D: Improved axial resolution.

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