Ch. 1 Physical Principles/ Doppler Imaging Flashcards
___: the difference between transmitted frequency and received frequency
Doppler shift
What are some factors that can cause spectral broadening?
-disease
-large sample volume
-can occur in normal vessels
Will PW or CW Doppler will always have spectral broadening and why?
CW because of the large sample volume (remember CW samples the whole length of the beam)
___: the filling in of the spectral window
Spectral broadening
___: number of cycles per second
Frequency
___: the number of pulses the US beam sends into the body each second
Pulse repetition frequency (PRF)
___: the time it takes the US beam to travel 1cm into the body and back
13 microsecond rule
What is the Doppler equation when solving for velocity
If this is the Doppler equation when solving for velocity what does each part represent and what is directly related
V= velocity
C= speed of sound in soft tissue (1540)
Fo= transducer freq
Cos 0= angle of incidence
Df= Doppler shift freq
Df and C are directly related with velocity
What is the Doppler equation when solving for Doppler freq
___: digital technique used to process both PW and CW Doppler
Fast Fourier transfer (FFT)
when the transducer has increased freq what happens to pen and res
increases freq= increased res, decreased pen
decreased freq= ___ res and ___ pen
decreased freq= decreased res, increased pen
what is the optimal angle of incidence for gray scale imaging
90 degrees
what is the optimal angle of incidence for doppler imaging
60 or less
which of the following has spectral broadening
the bottom one
how are frame rate and depth related
inversely, meaning increased depth = decreased frame rate
what artifact does this image show
aliasing
___: the ability of the system to properly display flow
Nyquist limit
what happens when PRF is greater than 1/2 the nyquist limit
aliasing
what are some things you can do to fix aliasing
-increase scale
-lower baseline
-lower freq
-use CW doppler (doesn't alias)
what is the speed of US through soft tissue
1540 m/sec
what are the two types of CW doppler
-analog
-digital or spectral
what are the benefits of CW doppler
does not alias
what are the cons of CW doppler
large sample volume (entire course of US beam)
when looking at this image of the color scale, which color is towards the transducer and which is away
top is always towards so in this case red
bottom is always away so in this case blue
steps to determine flow direction with color doppler
1. locate the top two corners of color box
2. draw line straight down, whichever is outside of the box is the side of your transducer
3. you will them look at your scale to determine if flow is moving towards or away from your transducer
is this flow moving towards or away from your transducer
toward
which vessel is moving toward the transducer and which is moving away?
SFA= toward
SFV= away
is the flow in this vessel moving toward or away from your probe?
toward
true or false: the vessel on the top is moving away from your transducer
true
how to determine flow direction with no color
1. draw a line straight down crossing through sample gate (some machines do this already)
2. Make the letter H with spectral gate
3. find where the lines intersect on the top and that is the side your probe is on
TIP: always remember + is towards - is away
which direction is this flow going?
away
what direction is this flow traveling?
toward
