Principles of colour and Spectral doppler

Question 1

What is the doppler effect?

Answer 1

Change in frequency of sound, light or other waves caused by the motion of the source or the observer

Question 2

In terms of ultrasound, the doppler effect is what?

Answer 2

The change in frequency of sound caused by the motion of red blood cells

Question 3

What is the basic formula for doppler for ultrasound?

Answer 3

Transmitted frequency - received frequency

Question 4

What is antegrade flow?

Answer 4

If the red blood cells are moving towards the transducer, the echo frequency will be larger than the transducer frequency

Question 5

What is retrograde flow?

Answer 5

If the cells are moving from the transducer, the echo frequency will be smaller

Question 6

What is beat frequency?

Answer 6

When the reflected wave will vary slightly from the original transmitted wave the algebraic sum gives off this frequency

Question 7

The method used to measure doppler shift is based on what?

Answer 7

Wave interference

Question 8

RBC move at different rates during what?

Answer 8

The cardiac cycle

Question 9

The RBCs speed up and slow down with ____ and _______ and will move at ________ ________ within a cross section of the ________. Cells closest to ____ ________ of the vessel move ________ than the ones near _______ ________.

Answer 9

1. Systole
2. Diastole
3. different speeds
4. Vessel
5. The center
6. Faster
7. The walls

Question 10

What is the detailed Doppler equation?

Answer 10

Question 11

Velocity is ______ to the doppler shift

Answer 11

Proportional

Question 12

Velocity in doppler is dependent on what?

Answer 12

Angle

Question 13

Doppler shift frequency is dependent on what?

Answer 13

Angle

Question 14

Doppler shift frequency is dependent on what?

Answer 14

Transducer frequency

Question 15

What is the Nyquist limitation?

Answer 15

1. The upper limit to the doppler shift that can be detected by pulsed instruments
2. Pulsed ultrasound must wait fro the first pulse to return before it can send out the second and so it is limited in how fast it can sample the RBC

Question 16

What is the formula for the Nyquist limitation? And what is the range?

Answer 16

1/2 PRF and is in the range of 5-30 kHz

Question 17

When the Nyquist limitation is exceeded what happens?

Answer 17

Aliasing occurs

Question 18

Why does aliasing happens?

Answer 18

1.The PRF is too slow for the true Doppler shift and is sampling the flow too late and only capturing parts of it.
2. The wave form is incomplete and appears to wrap around the baseline

Question 19

Aliasing is seen on colour doppler when what happens?

Answer 19

The colour “wraps” around the colour bar showing both colours in a vessel with no separation

Question 20

What can we do to compensate for aliasing?

Answer 20

1. Move the baseline
2. Increase the PRF (scale)
3. Increase the doppler angle
4. Lower the operating frequency
5. Change to CW

Question 21

What does the high PRF mode allows us to do?

Answer 21

Allows the machine to send out subsequent scan lines before the first is returned

Question 22

Having a high PRF mode might lead to what disadvantage?

Answer 22

Range ambiguity where the machine does not know what depth the echoes are being returned and could show misrepresented echoes on the display

Question 23

We can avoid the range ambiguity issue for high PRF mode if what happens?

Answer 23

If the Phantom SV does not lie in an artery or vein

Question 24

Doppler information can be represented in what 3 ways?

Answer 24

1. Spectral
2. Colour
3. Sound

Question 25

What is spectral doppler?

Answer 25

1. Graphed information show on on the display 2. Quantitive information in that you can precisely measure the speed of the RBCs at a given time by a process called FFT

Question 26

What is FFT?

Answer 26

1. Taking the complex beat frequency and dissecting it into the component waves. 2. Each component wave is the result of a reflection moving blood cells within the sample volume

Question 27

What is colour doppler?

Answer 27

When we can visualize flow in a vessel by first sending out scan lines to obtain 2D information and then another set of scan lines to obtain Doppler information

Question 28

Doppler information is overlaid on top of what?

Answer 28

The 2D scan

Question 29

What is autocorrelation?

Answer 29

When colour doppler is obtained and represents the mean or average of the flow velocity

Question 30

What is sound doppler?

Answer 30

Doppler shift information that can be heard

Question 31

What is a continuous wave doppler?

Answer 31

Sound waves emitted continuously from one crystal and reflected sound is continuously received by a second crystal

Question 32

What is the zone of sensitivity?

Answer 32

Velocities that come from a large overlap zone in CW

Question 33

What is an advantage and disadvantage of CW doppler?

Answer 33

No limit to the velocities that can be detected but the downside is that there is no range resolution or 2D image

Question 34

What is PW doppler?

Answer 34

1. When one crystal is used to fire and then listens for returning echoes. 2. Reception of the echoes is gated in time

Question 35

What is a benefit of PW doppler?

Answer 35

We know how fast the sound is travelling so we can determine at what depth we would like to sample.

Question 36

What does the range gate do for PW doppler? And what does the operator do?

Answer 36

Range gate determines where the sample volume will be positioned and the operator determines both the size of the gate and the depth.

Question 37

What is width of the sample volume equal to?

Answer 37

The width of the sample volume is equal to the beam width and its other dimensions are determined by the receiver gate length and the emitted pulse length

Question 38

How do we get a effective sample volume length, what is an example?

Answer 38

1. 1/2 of the pulse length is added to the gate length to yield the sample volume length 2. The pulse length shortens as the gate size is reduced

Question 39

What is colour doppler similar to?

Answer 39

Similar to colour doppler in that it is the overlay of colour onto the 2D image

Question 40

How do we obtain power doppler?

Answer 40

Instead of analyzing the doppler shift information, power doppler uses the amplitude of the returning doppler signals to detect flow.

Question 41

Because of how Power doppler is obtained, what does it result in?

Answer 41

It makes it very sensitive to low flow states and is independent of angle