Flashcards in Lesson 21 (Part 1) Deck (30)
What will happen tp the frequency if you are scanning a moving object like blood?
The returning frequency will not be the same
Change in frequency caused by the motion of a source, reflector or receiver
What is the source of the doppler effect in ultrasound?
What is the reflector of the doppler effect in ultrasound?
What is the receiver of the doppler effect in ultrasound?
What is changes in frequency caused by?
The motion of the reflector
The change in frequency
- delta f or fD
What does the change in frequency depend on?
Whether the object is moving closer or farther away
What is the formula for Doppler shift?
fD = fR-fT
fD = doppler shift
fR = received
fT = transmitted
What is the formula for delta F?
What does the frequency do when the doppler shift gets closer together?
- positive shift
What does the frequency do when the doppler shift gets farther apart?
- negative shift
What happens to the blood in a positive shift?
Blood moves towards the transducer
What happens to the blood in a negative shift?
Blood moves away from the transducer
What does it mean if you have 2 different colours in a doppler shift?
It is showing blood moving in two different directions
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
What happens when the doppler shift goes up?
Speed goes up
What happens when the doppler shift goes down?
Speed goes down
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)
What is the doppler shift?
Is the difference between the sent and returning frequencies of the sound wave
How can we affect the Doppler shift?
By changing the frequency
What do we use the Doppler shift to calculate?
What are examples of the doppler effect? (4)
1. Police speed detectors
2. Weather forecasting
3. Door openers
4. Burglar alarms
How is our probed compared to the blood flow?
Parallel to it
What happens if the angle of interrogation is non-zero?
Less Doppler shift will occur
How do we fix the lesser doppler shift?
By incorporating cos (cosine)
Angle between the sound beam and the vessel
What does doppler shift depend on?
The cosine of the doppler angle
What is the formula for fD with cos?
fD = 2fvcos/c
fD = doppler shift
f = fundamental frequency
v = velocity
cos = angle
c = propagation speed