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20 Cards in this Set
- Front
- Back
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Flow towards transducer _______frequency |
Increases |
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Doppler shift or change in Doppler frequency |
Back (Definition) |
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CW Doppler one crystal is continuously transmitting and one crystal is receiving signals. This causes |
Range ambiguity |
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Aliasing |
When high velocities appear negative Occurs with PW Doppler |
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Nyquist limit |
PRF/2 |
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Is color Doppler pulsed or continuous? 2D? |
Pulsed |
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Brightness of the image is improved by increasing |
Output Amplification - increases all signals the same way Compensation - creates uniform image. Takes depth into account. Does not increase every signal the same amount |
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If image is too bright |
Decrease output gain first |
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If image is too dark |
Increase receiver gain first (increases amplification after returning to receiver) |
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To increase sensitivity to low flow, nyquist limit should be |
Decreased Also decreases PRF |
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Define harmonic imaging |
Creating an image from sound reflected at twice the fundamental frequency |
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How is harmonic frequency created? |
Non linear behavior of sound causes energy to shift into higher frequencies by multiples of 2. Harmonics are typically created from strong beam in the main axis. Clearer image. |
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How does decreasing transducer frequency decrease aliasing? |
Causes less Doppler shift Velocity of blood in echo is extrapolated from frequency detected by machine. If there is less Doppler shift for a given high velocity, it can be detected without raising the PRF or nyquist limit.
Decreasing angle (Cos theta) similarly decreases Doppler shift |
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As imaging depth increases, PRF |
Decreases PRF = velocity/depth |
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Mechanical Index |
Back (Definition) |
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When using contrast if only the apex of LV is opacified |
Attenuating artifact Too much contrast! Increase the mechanical index temporarily to destroy some of the bubbles |
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Swirling artifact with contrast |
MI is too high, decrease to improve opacification |
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What is ideal mechanical index? |
Between 0.1 and 1 Promotes nonlinear resonance and harmonic enhancement |
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How quickly should myocardium perfume with contrast? |
Rest: within 5 beats Stress: within 2 beats |
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Strain rate |
Difference in velocities between 2 points / distance between 2 points |
