Principles of Colour and Spectral Doppler

Question 1

As velocity increases what happens to the doppler shift?

Answer 1

It increases

Question 2

What does velocity depend on?

Answer 2

The angle

Question 3

What does the doppler shift frequency depend on?

Answer 3

1. Angle

2. Transducer frequency

Question 4

What is the nyquist limit

Answer 4

1/2 PRF (Between 5-30 kHz

Question 5

What is autocorrelation?

Answer 5

A process that represents the mean or average flow of velocity in the vessel that allows for colour doppler

Question 6

What is the doppler effect?

Answer 6

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

Question 7

What is the doppler shift?

Answer 7

The diff between transmitted frequency (transducer) and received frequency (reflected/echo)

Question 8

What is antegrade flow, describe the shift.

Answer 8

RBC’s moving towards transducer (the echo frequency is larger than the transducer frequency).

Question 9

What is retrograde flow?

Answer 9

The RBC’s are moving away from the transducer (echo frequency smaller than transducer).

Question 10

What is the method used to measure the doppler shift?

Answer 10

Wave interference

Question 11

What is beat frequency?

Answer 11

The reflected wave differs from the original slightly and the sum of the two gives a resulting frequency called the beat frequency.

Question 12

Why are there many diff frequencies within the beat frequency?

Answer 12

Because the RBC’s speed up and slow down with systole and diastole and the cells closest to the centre move faster than near the walls.

Question 13

What is plotted in the spectral trace?

Answer 13

All of the frequencies contained within the beat frequency

Question 14

What is the doppler equation and what does it represent?

Answer 14

Change in F = 2 x Fo x V x Costheta / C

Represents: F(received) - F(transmitted)

Question 15

What is the doppler shift measured in and why can we hear it?

Answer 15

Measured in Hertz or kilohertz

In the “audible range” so we can hear it.

Question 16

Why does aliasing occur?

Answer 16

When the nyquist limit is exceeded the PRF is too slow and the sampling is only catching parts of the flow.

Question 17

How to compensate for aliasing? (5)

Answer 17

1. Move baseline
2. Increase PRF/scale
3. Increase doppler angle
4. Lower the operating frequency
5. Change to CW (sampling is continuous so no aliasing is possible)

Question 18

What is high PRF mode?

Answer 18

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

Question 19

What is a downside to high PRF mode?

Answer 19

Increases range ambiguity due to the machine not knowing what depth the echoes are being returned from.

Question 20

What ways can doppler info be represented?

Answer 20

1. Colour
2. Spectral
3. Sound

Question 21

What is FFT?

Answer 21

Fast Fourier Transformation

The method of graphing a spectral trace by taking the beat frequency and dissecting it into its component waves (individual reflections off of an RBC at a certain point in time).

Question 22

How is colour doppler info obtained?

Answer 22

Autocorrelation

Question 23

What is the zone of sensitivity?

Answer 23

In CW it is the area of overlap between the continuously emitted sound waves and the reflected sound waves.

Question 24

What is the benefit and drawbacks of CW?

Answer 24

Benefit = no limit to velocities that can be detected

Drawbacks = no range resolution/2d image

Question 25

How many crystals for CW?

Answer 25

Two

Question 26

How many crystals for PW?

Answer 26

One (transmits and then listens).

Question 27

How is spectral broadening affected by sample volume?

Answer 27

Large sample volume = more spectral broadening

Question 28

What does power doppler use to detect flow instead of the doppler shift?

Answer 28

Amplitude

Question 29

What is power doppler sensitive to?

Answer 29

Low flow states

Question 30

What is power doppler independent of?

Answer 30

Angle