ARDMS Updated SPI Exam Questions and Answers by huda

Lateral resolution describes the ability of an ultrasound system to distinguish between two structures that are side by side (perpendicular to the path of the ultrasound beam). This type of resolution depends on the beam width; narrower beams provide better lateral resolution. As the ultrasound beam travels deeper into the tissue, it generally widens, which can reduce lateral resolution. Techniques such as focusing the beam can help improve lateral resolution at specific depths by narrowing the beam width.

American Registry for Diagnostic Medical Sonography (ARDMS). Sonography Principles and Instrumentation (SPI) Examination Review Guide.

Axial resolution refers to the ability to distinguish two structures that are close to each other along the path of the ultrasound beam.

Spatial pulse length (SPL) is the distance over which one pulse occurs, and it directly affects axial resolution.

Shorter SPL improves axial resolution because it allows better differentiation of closely spaced structures.

The axial resolution is improved by increasing the frequency of the transducer, which shortens the wavelength and hence the SPL.References:

ARDMS Sonography Principles and Instrumentation guidelines on resolution parameters and their impact on image quality.

In the provided image, data below the baseline represents blood flow moving away from the transducer, which can indicate retrograde flow. When using spectral Doppler, the baseline separates flows towards and away from the transducer. Aliasing occurs when the velocity of blood flow exceeds the Nyquist limit, causing the display to wrap around and appear on the opposite side of the baseline. This phenomenon is common in high-velocity flow situations and results in part of the flow being displayed below the baseline. Retrograde flow further supports this, as it shows blood moving in the opposite direction to the expected flow.

Comprehensive and Detailed Explanation From Exact Extract:

Low PRF reduces the Nyquist limit, making the system more susceptible to aliasing when Doppler shift frequencies exceed this limit.

Principles and Instrumentation state:

"Aliasing occurs when Doppler shifts exceed half the PRF (Nyquist limit). Lowering PRF increases aliasing susceptibility."

Spectral broadening (A) results from turbulence or poor angle.

Range ambiguity (B) occurs at high PRF.

Dropout (D) refers to signal loss, not aliasing.

Therefore, the correct answer is C: Aliasing.

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