Lecture 21 Flashcards
(41 cards)
Ultrasound basics
A sound wave of a particular freq is sent out
It bounces off a stationary structure
It returns at the same frequency we sent out
Doppler effect
Change in freq caused by the motion of a source, reflector or reciever
Doppler of US
Change in frequency caused by the motion of the reflector
Doppler shift is
Change in frequency
Doppler shift
Depending on whether the object is moving closer or farther away, the freq will come back higher or lower
Doppler shift equation
units
Fd=fR-fT
KHz
In the doppler shift when thing are getting closer together frequency goes
Up
Postive shift
Doppler shift getting farther apart, frequency goes
Down
Gives a negative fD
Doppler shift equation with velocity
,, ,fD= 2 x f0 x v / c
,f0 - fundamental f aka transmitted fT
, v - speed of blood flow
, c- propag speed
Velocity equation
V= 77 x fD / f0
Units cm/ms
In doppler we (4)
Fire a particular frequency
Measure the frequency that returns
Figure out the doppler shift
Can calculate how fast an object is moving
What happens in doppler if frequency goes up
When frequency goes up doppler shift goes up
What happens when doppler shift goes up
Frequency goes up to compensate and velocity doesnt change
Were not directly affecting the _____ by changing the frequency
Velocity
The doppler shift is the different between
The sent and returning frequencies of the sound wave
Doppler effect
Police speed detectors
Weather forecasting
Door openers
Burglar alarms
So far with doppler angle we assume our probe is
Parallel to blood flow
If the angle of interrogation is non-zero _____ doppler shift will occur
Less
We incorporate ______ to compnsate for the lesser shift
cos (angl)
Doppler angle is
Angle between teh sound beam and the vessel
Cos 0
1
hitting the vessel straight on
Cos 30
0.87
Cos 60
0.5
Cos90
O
Hitting the vessel perpendicular
