Lesson 21 (Part 1) Flashcards Preview

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Flashcards in Lesson 21 (Part 1) Deck (30)
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1

What will happen tp the frequency if you are scanning a moving object like blood?

The returning frequency will not be the same

2

Doppler effect

Change in frequency caused by the motion of a source, reflector or receiver

3

What is the source of the doppler effect in ultrasound?

The transducer

4

What is the reflector of the doppler effect in ultrasound?

The tissue/RBC

5

What is the receiver of the doppler effect in ultrasound?

The transducer

6

What is changes in frequency caused by?

The motion of the reflector

7

Dopple shift

The change in frequency
- delta f or fD

8

What does the change in frequency depend on?

Whether the object is moving closer or farther away

9

What is the formula for Doppler shift?

fD = fR-fT
fD = doppler shift
fR = received
fT = transmitted

10

What is the formula for delta F?

kHz

11

What does the frequency do when the doppler shift gets closer together?

It increases
- positive shift

12

What does the frequency do when the doppler shift gets farther apart?

It decreases
- negative shift

13

What happens to the blood in a positive shift?

Blood moves towards the transducer

14

What happens to the blood in a negative shift?

Blood moves away from the transducer

15

What does it mean if you have 2 different colours in a doppler shift?

It is showing blood moving in two different directions

16

What do we do in Doppler? (4)

1. We fire a particular frequency
2. We measure the frequency that returns
3. We figure out the Doppler shift
4. We can calculate how fast an object is moving

17

What happens when the doppler shift goes up?

Speed goes up

18

What happens when the doppler shift goes down?

Speed goes down

19

What does changing the frequency affect?

It wont affect the rate of velocity
- we do not directly affect the velocity by changing the frequency (the speed doesnt change because we are changing the probe)

20

What is the doppler shift?

Is the difference between the sent and returning frequencies of the sound wave

21

How can we affect the Doppler shift?

By changing the frequency

22

What do we use the Doppler shift to calculate?

Velocity

23

What are examples of the doppler effect? (4)

1. Police speed detectors
2. Weather forecasting
3. Door openers
4. Burglar alarms

24

How is our probed compared to the blood flow?

Parallel to it

25

What happens if the angle of interrogation is non-zero?

Less Doppler shift will occur

26

How do we fix the lesser doppler shift?

By incorporating cos (cosine)

27

Doppler angle

Angle between the sound beam and the vessel

28

What does doppler shift depend on?

The cosine of the doppler angle

29

What is the formula for fD with cos?

fD = 2fvcos/c
fD = doppler shift
f = fundamental frequency
v = velocity
cos = angle
c = propagation speed

30

What is the formula for v with cos?

v = 77fD/fcos
v = velocity
fD = doppler shift
f = fundamental frequency
cos = angle