# Module 5- Just Doppler Imaging Flashcards

What are other names for the Doppler effect?

- Doppler Shift
- Frequency Shift
- Doppler Frequency
- Beat Frequency

What is the Doppler effect?

A change in the observed/received frequency of a wave due to the motion of the source, the observer, or both (relative to each other)

What is the Doppler effect used for?

Used to determine:

- The velocity of the moving reflectors (red blood cells)
- Direction of flow

What is a positive Doppler shift?

Flow towards the transducer

What is a negative Doppler Shift?

Flow away from the transducer

What happens if the receiver is moving towards the stationary source?

- Increase in frequency
- sound source sends out a wave
- the receiver meets each wave-crest more quickly than if stationary
- the receiver detects more complete wavelengths per second (so a higher frequency)

What happens if both the sound source and receiver are stationary?

No change in frequency (between the transmitted and received frequency)

What happens if the receiver is stationary and the source is moving away from it?

- Decrease in frequency
- Creates a longer wavelength and a lower frequency

What happens if the receiver is stationary and the source is moving towards it?

- Increase in frequency
- creates a shorter wavelength and a higher frequency

What happens if both the source and the receiver are moving in the same direction at the same speed?

-No Doppler shift is observed

no change in frequency

How can a Doppler shift occur if the source and receiver are both moving in the same direction?

If they are moving at different speeds

What are the advantages of continuous wave Doppler?

- No upper limit to velocity
- No aliasing
- Small probe sizes
- Ability to use higher frequencies

What is a disadvantage of continuous wave Doppler?

Range ambiguity ( can’t tell where the echo is coming from)

In continuous wave Doppler, when is the change in voltage detected?

When the wave returns to the receiver

What is continuous wave Doppler?

- Uses 2 crystals

- The beam is directional, with an area of overlap which is where the Doppler signals will read

How is the frequency of CW Doppler determined?

The applied voltage

What is the advantage of Pulsed wave Doppler?

Range resolution (knowing where the Doppler signals are coming from)

What is the disadvantage of Pulsed wave Doppler?

Aliasing

What is pulsed wave Doppler?

- 1 crystal

- A sample volume or gate is placed in the vessel from which the Doppler info is desired

What is range resolution?

- Only signals (reflectors) from within the sample gate will be processed
- Allows the sonographer to know exactly where the Doppler information is being derived from
- The opposite of range ambiguity

What is the Nyquist limit?

1/2 PRF (the PRF of the Doppler)

-The level at which aliasing will begin to occur

TRUE/FASLE: Pulses used in Pulsed Doppler are longer than pulses used in imaging systems.

TRUE

Are longer or shorter pulses needed to properly determine Doppler frequency of returning echoes?

Longer

What is the formula for Doppler Shift (∆F)?

c

(Fo being incident frequency)

(v = velocity of RBCs)

(cosθ being the cosine of the incident angle)

What is the cosine of 0°?

1

What is the cosine of 45°?

.70 (.76 to Sherrill)

What is the cosine of 60°?

.5

What is the cosine of 90°?

0

What is the Doppler shift formula written to calculate the reflector speed?

2 x Fo x cosθ

(∆F being the Doppler shift)

(Fo being the incident frequency)

If there is a lower receiving frequency than sending frequency, which direction is it going?

Away (final is greater than initial)

If there is a higher receiving frequency than sending frequency, which direction is it going?

Towards (final is less than initial)

What is the relationship between the Doppler shift (∆F) and the angle (θ)?

- ∆F increases

- θ decreases

What must be know to calculate an accurate velocity?

The cosine of the angle

What scenario would you not need the cosine of the angle to determine the velocity of the flow?

If you are dead on to the flow (coming straight at you)

What is the relationship between Doppler shift (∆F) and Incident frequency (Fo)?

DIRECT

- ∆F increases
- Fo increases

What is the relationship between Doppler shift (∆F) and velocity of the reflector?

DIRECT

- ∆F increases
- v increases

What is the relationship between cosθ and Doppler shift (∆F)?

DIRECT

- cosθ increases
- ∆F increases

What is the relationship between the cosθ and the angle (θ)?

INVERSE

- cosθ increases
- θ decreases