Doppler edelman ch 19 and color doppler pp, spectral analysis pp Flashcards
(87 cards)
doppler shift is also called _________
doppler frequency
the process of extracting the low doppler frequency from the transducer carrier frequency is called ____________
demodulation
doppler shift(Hz) equation
doppler shift(Hz)= reflected frequency - transmitted frequency
if doppler shift is positive (frequency higher than the transmitted frequency), what does that mean
blood cells are traveling toward the transducer
doppler frequencies indicate __________, not speed
velocity
speed vs velocity
speed in magnitude
velocity is magnitude and direction
when velocity is halved, the doppler shift is __________
halved
flow towards transducer is where on baseline
above baseline
simultaneous anatomic imaging and doppler is called _______________
duplex imaging
what term is used for bidirectional doppler
phase quadrature or quadrature detection
what is the most common error associated with doppler ultrasound
aliasing
what is the very top or very bottom of the spectral display called
nyquist limit
what is the part of the spectrum that appears on the the opposite side after reaching its limit
aliasing
can aliasing happen with continuous wave doppler
No, only with pulsed doppler
nyquist limit (hz) equaltion
= PRF(HZ) / 2
2 ways to avoid aliasing are
raise the nyquist limit
reduce the doppler shift
produces a continuously alternating voltage that drives the element
Oscillator
detects the difference between source and reflected frequency & determines the Doppler shift (Doppler shift are normally in the audible range and are applied to a loudspeaker)
Doppler detector
analyzes the spectrum for visual display
Spectrum analyzer
Doppler detector that has the ability to determine positive and negative shifts contained in incoming echoes and to separate them into two channels for display
-Two output channels
-Represents forward (positive Doppler shift) and reverse flow (negative Doppler shift)
Phase quadrature detector
Performed by a high-pass (wall) filter
-Eliminates high-intensity, low-frequency
Doppler shift echoes resulting from
vessel or heart wall motion
-Rejects strong echoes that obstruct
weaker echoes
Wall filter
ADJUST WALL FILTER WHEN NEAR WALL
Same crystal to both transmit and receive
Presents one-dimensional information audibly and visibly
Has the ability to select listening depth
PULSED WAVE DOPPLER
Allows operator to separate flow information from two vessels or to localize within a vessel
-Uses a “gate”
-When open, allows the passage of voltages representing echoes; when closed, prevents the passage of voltages
- Determined using echo-arrival time (corresponds to depth of reflector)
-Gate should be open to 1/2 width of the vessel to prevent artifactual spectral broadening
Range selectivity -
Pulser generates pulses of ___________ cycles
PULSED WAVE DOPPLER
5-30 cycles