The duty factor is the fraction of time that the ultrasound system is actively transmitting a signal. Continuous wave (CW) Doppler has the highest duty factor because it continuously transmits and receives ultrasound waves. Unlike pulsed wave Doppler, which alternates between sending and receiving signals, CW Doppler does not have a listening period, resulting in a duty factor of nearly 100%. Therefore, CW Doppler has the highest duty factor among the modes listed.
Reject: This control eliminates low-level noise and weak signals, affecting image quality but not primarily used for contrast resolution.
Output Power: This adjusts the intensity of the transmitted ultrasound waves but does not directly change contrast resolution.
Gain: This control amplifies all signals equally, affecting brightness but not specifically the contrast resolution.
Dynamic Range: Adjusting the dynamic range changes the range of grayscale that the ultrasound system displays, which directly affects the contrast resolution by altering how many shades of gray are visible between the black and white extremes.
[References:, "Understanding Ultrasound Physics" by Sidney K. Edelman, ARDMS Sonography Principles and Instrumentation study materials, , , ]
Question 54
Which factor causes posterior acoustic enhancement?
High-Frequency Transducer: These provide better resolution but do not directly cause posterior enhancement.
Low-Frequency Transducer: These provide better penetration but are not the cause of posterior enhancement.
Strongly Attenuating Structure: This would cause acoustic shadowing rather than enhancement.
Weakly Attenuating Structure: Structures that attenuate the ultrasound beam less than the surrounding tissues allow more sound waves to pass through, resulting in increased brightness or "enhancement" behind the structure.
[References:, "Ultrasound Physics and Instrumentation" by Frank Miele, ARDMS Sonography Principles and Instrumentation study materials, , ]
Question 55
What method can be used to resolve aliasing artifact?
Comprehensive and Detailed Explanation From Exact Extract:
Continuous wave (CW) Doppler can measure very high velocities without aliasing because it does not have a Nyquist limit like pulsed-wave Doppler.
Principles and Instrumentation state:
"Aliasing is eliminated in continuous wave Doppler since it does not rely on sampling and has no upper velocity limit."
Output power (A) affects signal strength, not aliasing.
Higher frequency (B) increases aliasing susceptibility.
Decreasing PRF (C) actually worsens aliasing.
Therefore, the correct answer is D: Using continuous wave Doppler ultrasound.
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