Doppler Ultrasound Flashcards
What is the Doppler effect used to measure?
Blood speed
What is the ultrasound Doppler shift measured by?
Comparing transmitted and received ultrasound signals (usually pulses)
What is found within a single location?
Spectral Doppler
Over a region: (colour/power)
Doppler Imaging
What is doppler shift proportional to?
Blood speed (m/s or cm/s) for a fixed angle between artery (direction of blood flow) and ultrasound beam direction
Why do you need to calibrate the machine?
Get a good estimate of the speed of blood
How do you calculate the sped in m/s?
Calculate the cross-sectional area and multiply the speed by that cross sectional area
= units of m3/second
What gives an indication of blood flow?
Measure the average of speed and multiple that by cross section
What is B-more image?
Grey-level image that is displayed
Provide anatomical information but doesn’t tell anything about speed or blood
What is blood flow colour coded according to?
Direction
The direction is relative to ultrasound waves
What is veins displayed as?
Shades of blue and green
What is spectral Doppler trace?
Measuring speed of blood at a particular point
Measuring within middle of artery - between 2 little gates
Why is the line angled so that it is in same direction as the artery?
So it will be close to the direction of blood
Where is the ultrasound transducer placed on?
Skin
What is it called when we want to measure at a specific speed?
Sample volume
What is aligned with the vessel?
Angle correction line
What does the spectral Doppler trace tend to measure?
Blood velocity which corresponds to the blue line which is the envelope
What is the envelope in the spectral Doppler trace?
Maximum velocity speed that is being measured
What gives the spectral broadening shape?
Spread of speed within a sample of small volume
Where is there a proportionality between?
Doppler shift and speed of blood
What is kept constant in the Doppler equation?
speed of sound
Around 15-40m/second
What is measured by the ultrasound scanner?
- Doppler shift
- Received frequency
- Transmitted frequency
What is set by the scanner operator?
Doppler angle < = 60 deg
What is known by ultrasound scanner?
- transmitted frequency
2. Speed of sound
What is doppler shift thereotically?
0
Theta=90degree
What is the best practice for doppler velocity measurement?
Theta < 60 degree and fixed