Colour and Power Doppler Flashcards
What determines the mean and variance of the Doppler-shifted signal for each scan line? (hint: multiple pulses used to determine velocity)
Autocorrelation
Autocorrelation occurs in which of the following?
a) Beam former
b) Signal processor
c) Image processor
d) Display
B
In linear array colour doppler scanning, what is used in each scan line to avoid perpendicular angles?
Phasing
What is known as the number of pulses per COLOUR scan line?
Ensemble length AKA packet size
What are the benefits and disadvantages of increased ensemble length?
- Improved velocity accuracy
- Improved colour accuracy
- Slower blood flow
- Disadvantage = LOWER frame rate
Frame Rate and colour doppler are dependent on what 3 things?
- Box width
- Ensemble length
- Box depth
What occurs when the DSF exceeds the nyquist limit?
Aliasing
What is the Nyquist limit?
1/2 PRF - highest detectable doppler shifted frequency without aliasing
What is the amplitude of the colour signal refer to?
Brightness
What is known as “moving up or down the color map”?
Saturation
On colour maps, what does the baseline represent?
Zero or near zero doppler shift
What are the colour velocity ranges for
Carotid, venous, and cardiac imaging?
Carotid - 30-40 cm/s
Venous - < 20
Cardiac - 60-80
What is the PRF?
2 x Nyquist limit
Purpose of wall filters?
Eliminate low doppler shift frequencies (eliminates clutter)
What happens to the wall filter as the colour scale increases?
Wall filter also increases which will eliminate higher DSF
T or F? In colour doppler gain imaging, every pixel displayed has the same level of brightness or amplitude, unlike 2D gain
TRUE
What artifact is seen when colour gains are too high?
Bleeding
What is known as frame to frame averaging in order to smooth out the colour appearance by reducing noise (speckle)?
Persistence
What is a threshold technique set by the user that determines if the pixel is displayed as colour or gray scale?
Colour priority
In power doppler, what is the doppler shift determined by?
Concentration of the moving scatterers
What is power doppler based on?
Amplitude
Power doppler uses frame averaging. What kind of resolution does this decrease?
Temporal
In power doppler, what artifact is shown due to relative motion between the transducer and patient?
Flash
