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Sam's Physics II > Chapter 18, 19 and 20 Study Guide > Flashcards

Chapter 18, 19 and 20 Study Guide Flashcards

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1
Q

Pulsed Doppler

A

range resolution
sample volume
limited maximum velocity-Nyquist
aliasing

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2
Q

Continuous Wave Doppler

A

range ambiguity
region of overlap
unlimited maximum velocity
no aliasing

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3
Q

Pulsed Doppler Transducer

A 
at least one crystal 
dampened PZT 
low Q-factor 
wide bandwidth 
low sensitivity
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4
Q

Continuous Doppler Transducer

A 
at least two crystals 
undampened PZT 
high Q-factor 
narrow bandwidth 
higher sensitivity
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5
Q

Imaging

A

normal incidence- 90 degrees
higher frequency- improves resolution
pulsed wave only
minimum of 1 crystal

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6
Q

Doppler

A

0 to 180 degrees
lower frequency- avoids aliasing
minimum of 1 (pulsed) or 2 (continuous wave) crystals

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7
Q

What is the movement of fluid from one location to another called?

A

velocity

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8
Q

Fluid moving with a variable velocity when it accelerates and decelerates, what is that called?

A

Pulsatile Flow
accelerates and decelerates as a result of cardiac contraction
appears in the arterial circulation

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9
Q

What is fluid moving from one location to another and it accelerates and decelerates with respiration?

A

Phasic Flow

appears in the venous circulation

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10
Q

What type of flow pattern will be seen with normal physiological states?

A

Laminar Flow

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11
Q

Frictional loss occurs when one object rubs against another, blood sliding along the vessel wall would be considered what?

A

Frictional loss

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12
Q

The Reynolds number for turbulent flow is what?

A

greater than 2,000

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13
Q

What are the effects of stenosis?

A 
change in flow direction 
turbulence downstream from the stenosis 
increased velocity as vessel narrows 
pressure gradient across the stenosis 
loss of pulsatility
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14
Q

What information is the Doppler shift providing?

A

velocities of blood cells

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15
Q

What is a positive Doppler shift?

A

when blood cells move toward the transducer

the reflected frequency is higher than the transmitted frequency

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16
Q

What is a negative Doppler shift?

A

when blood cells move away from the transducer

the reflected frequency is lower than the transmitted frequency

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17
Q

Hydrostatic Pressure

A

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

18
Q

Hydrostatic Pressure: Supine and Standing

A

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

19
Q

What is the typical range of Doppler shift found in imaging exam?

A

20 Hz to 20,000 Hz (20 KHz)

audible range

20
Q

What are the 5 ways to eliminate aliasing?

A 
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
21
Q

What does the Y axis stand for on the Doppler spectrum?

A

Doppler shift or velocity

22
Q

What does the X axis stand for on the Doppler spectrum?

A

time

23
Q

What two things are the gray shades related to on the Doppler spectrum?

A

amplitude of the reflected signal

number of blood cells creating reflection

24
Q

When we look at our Doppler spectrum and see our waveform is high, are we using a higher or lower frequency?

A

higher frequency
the Doppler shift is directly proportional to the transducer frequency. When the transmitted frequency doubles, the Doppler frequency doubles.

25
Q

What is speed?

A

speed = distance/time

26
Q

What is velocity?

A

velocity = speed with direction

27
Q

What is the primary advantage for pulsed wave Doppler?

A

being able to select the exact location where velocities are measured

28
Q

What is the primary advantage for continuous wave?

A

to accurately measure very high velocities

29
Q

Bidirectional Doppler uses what kind of processing?

A

phase quadrature or quadrature detection

30
Q

What type of velocities does color flow measure?

A

average (mean) velocity

31
Q

Autocorrelation

A

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)

32
Q

Color Flow

A

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

33
Q

What are the limitations to color flow imaging?

A

provides information on the location of flow:

is a pulsed ultrasound technique
has a range resolution (range specificity)
is subject to aliasing

34
Q

What are the advantages of Doppler Packets?

A

more accurate velocity measurement

increased sensitivity to low flow

35
Q

What are the disadvantage of Doppler Packets?

A

more time needed to acquire data
reduced frame rate
decreased temporal resolution

36
Q

Inspiration

A 
diaphragm moves downward toward the abdomen 
thoracic pressure decreases 
abdominal pressure increases 
venous return to the heart increases 
venous flow in legs decreases
37
Q

Expiration

A 
diaphragm moves upward into thorax 
thoracic pressure increases 
abdominal pressure decreases 
venous return to the heart decreases 
venous flow in legs increases
38
Q

When venous pressure is low, what is the volume of blood in the veins?

A

when veins have low pressure, they are only partially filled with blood and only partially expanded

39
Q

What happens to the shape of the vein when the venous pressure increases?

A

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

40
Q

What is Doppler shift inversely related to?

A

propagation speed

41
Q

What is Fast Fourier Transform used for?

A

to process both pulsed and continuous wave Doppler signals

distinguishes laminar flow from turbulent flow

42
Q

When the sample volume is deep the PRF is what? And the nyquist limit is what?

A

PRF is low and Nyquist is low

deeper sample volumes have a lower pulse repetition frequency and create aliasing

Sam's Physics II (7 decks)

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