COS Theta
Angle between the sound beam and direction of motion
What is duplex imaging?
Simultaneous anatomical images and doppler
What would the measured pressure of a standing patient with a material pressure of 120mmHg at the level of the ankles?
220mmHg
What does spectral doppler measure in regards to velocity?
Peak velocity
They very top of the display is called the
Nyquist limit
What is the equation for measured velocity?
True velocity x COS (theta)
What are the advantages and disadvantages of a continuous wave doppler?
Advantage: Accurately measure very high velocities
Disadvantages: Range ambiguity and lack of TGCs
During inspiration, blood flow to the heart
A negative doppler shift indicates blood cells moving _____ from the transducer. A positive doppler shift indicates blood cells moving ______ from the transducer.
Away; towards
Aliasing is also called the _____ _______
False identity
Which COS creates the best image, but is bad for doppler?
COS 0
What characteristics (4) result from a lack of backing material used in continuous wave dopplers?
undamped signal, narrow bandwidth, high Q factor, and higher sensitivity
What would the measured pressure be of a supine patient with a arterial pressure of 110mmHg at the level of the head?
110mmHg
How many crystals are used in a continuous wave doppler transducer and what are they/it used for?
Two, one receives and one transmits
Aliasing in pulsed wave doppler is defined as
Very high velocities in one direction are correctly displayed as going in the opposite direction.
Doppler shift is _____ to the cosine of the angle between the direction of flow and the direction of sound
Directly
Flow towards the transducer is displayed _____ the baseline.
Above
During expiration, thoracic pressure
Is color flow doppler subject to aliasing?
Yes
What is the Nyquist limit?
Why would a angle of 0 be the most accurate, but is not possible to create?
The sound beam would be parallel to the blood cells, impossible to do externally
What is the doppler shift equation?
2 x Tx frequency x velocity x COS(theta) / propagation speed
What is the formula for measured pressure?
Circulatory pressure + hydrostatic pressure
Name the five techniques used to reduce aliasing:
1. Adjust scale to max
2. New shallower view
3. Lower frequency tx
4. Use baseline shift
5. Use continuous wave doppler
The Nyquist limit is _/_ the PRF
1/2