Lecture 21 Flashcards
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
Decreased dopller shift measurement = _____ velocity measurement
Decreased
Techniques to get closer to 0 degrees
Heel toe
Phase (steer)
Angle correct
Angle correct on US machine
Tell the machine that were off and it compensates, increases the velocity back to where it should be
Increase in doppler angle, the ____ error in the speed calculation
Increase
0 degree = ____% error
0.4%
70 degrees = ____% error
32%
In real life we work under _____ degrees
60
Doppler displays
Colour
Spectral
Audible
Colour doppler aka
Colour flow imaging
Colour doppler defined by
Presence, speed, charactter and direction of flow
Colour doppler assess a _____ area at a time
Very large compared to spectral doppler
Colour ___________ on gray scale image
Superimposed
Colour doppler often steeres via ____, to get closer to ____ degree to avoid if vessels are parallel to the surface
Phasing
90 degrees
If returning echoes have a different freq than from emitted, ________ has occured
Doppler shift
Depending on the sign of doppler shift
Its towards or away
Colour will be assigned to pixels
In colour doppler, multiple _______ are sent per _______
Pulses are sent per scan line
Vs. One per scan line in B mode
Doppler shift is calculated within
The signal processor
