Chapter 18, 19 and 20 Study Guide Flashcards
Pulsed Doppler
range resolution
sample volume
limited maximum velocity-Nyquist
aliasing
Continuous Wave Doppler
range ambiguity
region of overlap
unlimited maximum velocity
no aliasing
Pulsed Doppler Transducer
at least one crystal dampened PZT low Q-factor wide bandwidth low sensitivity
Continuous Doppler Transducer
at least two crystals undampened PZT high Q-factor narrow bandwidth higher sensitivity
Imaging
normal incidence- 90 degrees
higher frequency- improves resolution
pulsed wave only
minimum of 1 crystal
Doppler
0 to 180 degrees
lower frequency- avoids aliasing
minimum of 1 (pulsed) or 2 (continuous wave) crystals
What is the movement of fluid from one location to another called?
velocity
Fluid moving with a variable velocity when it accelerates and decelerates, what is that called?
Pulsatile Flow
accelerates and decelerates as a result of cardiac contraction
appears in the arterial circulation
What is fluid moving from one location to another and it accelerates and decelerates with respiration?
Phasic Flow
appears in the venous circulation
What type of flow pattern will be seen with normal physiological states?
Laminar Flow
Frictional loss occurs when one object rubs against another, blood sliding along the vessel wall would be considered what?
Frictional loss
The Reynolds number for turbulent flow is what?
greater than 2,000
What are the effects of stenosis?
change in flow direction turbulence downstream from the stenosis increased velocity as vessel narrows pressure gradient across the stenosis loss of pulsatility
What information is the Doppler shift providing?
velocities of blood cells
What is a positive Doppler shift?
when blood cells move toward the transducer
the reflected frequency is higher than the transmitted frequency
What is a negative Doppler shift?
when blood cells move away from the transducer
the reflected frequency is lower than the transmitted frequency
Hydrostatic Pressure
pressure related to the weight of blood pressing on a vessel measured at a height above or below the heart level
units: mmHg (the same units used for blood pressure)
when supine: all parts of the body are at the level of the heart and hydrostatic pressure is 0
Hydrostatic Pressure: Supine and Standing
supine: all parts of the body are at the level of the heart and hydrostatic pressure is 0
standing: hydrostatic pressure depends on if the measurement is taken above or below the heart
measurements below the heart: will be positive
measurements above the heart: will be negative
measured pressure = circulatory pressure + hydrostatic pressure
What is the typical range of Doppler shift found in imaging exam?
20 Hz to 20,000 Hz (20 KHz)
audible range
What are the 5 ways to eliminate aliasing?
adjust the scale to its maximum select a lower frequency transducer select a new ultrasound view with a shallower sample volume use a baseline shift use continuous wave Doppler
What does the Y axis stand for on the Doppler spectrum?
Doppler shift or velocity
What does the X axis stand for on the Doppler spectrum?
time
What two things are the gray shades related to on the Doppler spectrum?
amplitude of the reflected signal
number of blood cells creating reflection
When we look at our Doppler spectrum and see our waveform is high, are we using a higher or lower frequency?
higher frequency
the Doppler shift is directly proportional to the transducer frequency. When the transmitted frequency doubles, the Doppler frequency doubles.
What is speed?
speed = distance/time
What is velocity?
velocity = speed with direction
What is the primary advantage for pulsed wave Doppler?
being able to select the exact location where velocities are measured
What is the primary advantage for continuous wave?
to accurately measure very high velocities
Bidirectional Doppler uses what kind of processing?
phase quadrature or quadrature detection
What type of velocities does color flow measure?
average (mean) velocity
Autocorrelation
is a digital technique used to analyze color flow Doppler
uses color Doppler because of the enormous amount of data that is processed
less accurate but faster to perform than FFT (fast fourier transform)
Color Flow
a form of two-dimensional Doppler
velocity is coded into colors (away and towards flow)
black and white identifies anatomic structures
color identifies blood flow
What are the limitations to color flow imaging?
provides information on the location of flow:
is a pulsed ultrasound technique
has a range resolution (range specificity)
is subject to aliasing
What are the advantages of Doppler Packets?
more accurate velocity measurement
increased sensitivity to low flow
What are the disadvantage of Doppler Packets?
more time needed to acquire data
reduced frame rate
decreased temporal resolution
Inspiration
diaphragm moves downward toward the abdomen thoracic pressure decreases abdominal pressure increases venous return to the heart increases venous flow in legs decreases
Expiration
diaphragm moves upward into thorax thoracic pressure increases abdominal pressure decreases venous return to the heart decreases venous flow in legs increases
When venous pressure is low, what is the volume of blood in the veins?
when veins have low pressure, they are only partially filled with blood and only partially expanded
What happens to the shape of the vein when the venous pressure increases?
the cross-sectional shape of a vein change from hourglass to oval and then to round
hourglass > oval > round
this allows veins to accommodate a large volume increase with a small increase in pressure
What is Doppler shift inversely related to?
propagation speed
What is Fast Fourier Transform used for?
to process both pulsed and continuous wave Doppler signals
distinguishes laminar flow from turbulent flow
When the sample volume is deep the PRF is what? And the nyquist limit is what?
PRF is low and Nyquist is low
deeper sample volumes have a lower pulse repetition frequency and create aliasing
