The purpose of using a spectral Doppler wall filter is to eliminate lower velocity signals. Wall filters are designed to remove low-frequency Doppler shifts caused by the motion of the vessel walls or surrounding tissues, which are generally of no diagnostic value. By eliminating these lower velocity signals, the wall filter helps to clean up the Doppler signal and reduce clutter, allowing for a clearer and more accurate display of blood flow velocities.
Reference:
ARDMS Sonography Principles and Instrumentation (SPI) Exam Study Guide
"Diagnostic Ultrasound: Principles and Instruments" by Frederick W. Kremkau

Comprehensive and Detailed Explanation From Exact Extract:
Sensitivity refers to the system's ability to detect and display weak echoes, such as those from low-amplitude reflectors or deeper structures.
According to Principles and Instrumentation:
"Sensitivity is the minimum echo strength that the system can detect and display, directly related to its ability to image low-level echoes." Slice thickness refers to elevational resolution.
Axial and lateral resolution refer to spatial detail, not echo strength detection.
Therefore, the correct answer is C: Sensitivity.
-

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.
-

Attenuation in ultrasound is directly proportional to the path length. If the path length is doubled, the amount of attenuation is also doubled. Attenuation refers to the reduction in the amplitude and intensity of the ultrasound wave as it travels through tissue, primarily due to absorption, reflection, and scattering. The relationship is linear, so doubling the distance the sound wave travels will result in twice the amount of attenuation.
Reference:
ARDMS Sonography Principles and Instrumentation guidelines
Kremkau, F. W. (2015). Diagnostic Ultrasound: Principles and Instruments. Elsevier.

Comprehensive and Detailed Explanation From Exact Extract:
The Doppler equation shows that the frequency shift is proportional to the cosine of the Doppler angle. The maximum value of cosine (cos 0° = 1) occurs at 0 degrees - meaning the beam is parallel to flow. At this angle, the full velocity component is measured.
According to sonography instrumentation reference:
"The maximum Doppler shift is obtained when the ultrasound beam is parallel (0 degrees) to blood flow." Therefore, the correct answer is D: 0 degrees.
-