Podcast
Questions and Answers
In what scenario is aliasing most likely to occur?
In what scenario is aliasing most likely to occur?
Which of the following methods can effectively resolve aliasing?
Which of the following methods can effectively resolve aliasing?
What color is typically displayed in the absence of a Doppler shift?
What color is typically displayed in the absence of a Doppler shift?
What does the Nyquist Limit represent in relation to PRF?
What does the Nyquist Limit represent in relation to PRF?
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Which utility controlled by the user amplifies the amplitude of Doppler shifts?
Which utility controlled by the user amplifies the amplitude of Doppler shifts?
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Study Notes
Aliasing
- Occurs when the Doppler shift exceeds the Nyquist Limit.
- This happens when blood flow is moving very fast
- Can also occur when the PRF (Pulse Repetition Frequency) is set too low.
Correcting for Aliasing
- Several methods can be used to correct for aliasing:
- Adjust the scale: This increases the Nyquist Limit, allowing for higher flow velocities to be measured.
- Adjust the baseline: This shifts the displayed Doppler signals, potentially bringing aliased signals within the measurable range.
- Switch to continuous wave (CW): CW Doppler does not rely on PRF, eliminating the potential for aliasing.
- Adjust the PRF: Increasing the PRF directly increases the Nyquist Limit, thereby reducing the likelihood of aliasing.
Doppler Shift
- No Doppler shift is displayed as black.
Gain
- A user-controlled setting that amplifies the amplitude of Doppler shifts, making them brighter on the screen.
Doppler Angle & Doppler Shift
- An inverse relationship exists between the Doppler angle and the Doppler shift.
Nyquist Limit
- The maximum value of the scale.
- The Nyquist Limit is half the PRF (Pulse Repetition Frequency).
Wall Filter
- A filter used to reject or delete low-amplitude Doppler shifts, often used to remove signals from stationary tissues like vessel walls).
Common Doppler Artifact
- Aliasing is the most commonly encountered artifact in Doppler.
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Description
Test your knowledge on the complexities of aliasing in Doppler ultrasound. This quiz covers the causes of aliasing, methods for correction, and important concepts such as Doppler shift and gain. Ideal for students and professionals in the field of medical imaging.
