Lesson 21 (Part 1) Flashcards
What will happen tp the frequency if you are scanning a moving object like blood?
The returning frequency will not be the same
Doppler effect
Change in frequency caused by the motion of a source, reflector or receiver
What is the source of the doppler effect in ultrasound?
The transducer
What is the reflector of the doppler effect in ultrasound?
The tissue/RBC
What is the receiver of the doppler effect in ultrasound?
The transducer
What is changes in frequency caused by?
The motion of the reflector
Dopple shift
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?
kHz
What does the frequency do when the doppler shift gets closer together?
It increases
- positive shift
What does the frequency do when the doppler shift gets farther apart?
It decreases
- 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)
- We fire a particular frequency
- We measure the frequency that returns
- We figure out the Doppler shift
- 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?
Velocity
What are examples of the doppler effect? (4)
- Police speed detectors
- Weather forecasting
- Door openers
- 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)
Doppler angle
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
What is the formula for v with cos?
v = 77fD/fcos v = velocity fD = doppler shift f = fundamental frequency cos = angle
