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Ultrasound Physics > Chapters 18 & 19 Blood Hydrodynamics & Doppler > Flashcards

Chapters 18 & 19 Blood Hydrodynamics & Doppler Flashcards

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0
Q

What are important measurements in hydrodynamics?

A

Flow-volume per time (m/sec) how much blood is traveling from one area to another.

Velocity- this shows the speed and direction of blood flow (cm/sec): how fast is that blood moving.

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1
Q

What is hydrodynamics why is it important to understand?

A

The study of blood in the circulatory system

for the understanding of PV, HV and TIPSS, and vascular disease process in the vascular US.

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2
Q

Name and describe the different types of flow.

A

Pulsatile flow- different velocities at different times, this is found in the arterial system and produced by the pumping of the heart, also seen in systems like the testies, OV, and AO spectral doppler.

Phasic Flow- his has a velocity of different speeds, at different times because of respiration, found in most venous systems, such as the MPV, and IVC spectral doppler

Steady flow- this a constent velocity, such as when the patient is holding their breath, seen in venous spectral Doppler.

Laminar Flow- uniform direction of flow. rings of flowing blood, there are 2 types depending on flow profile.

Turbulent flow- blood flowing in different directions, it occures normaly at a branching of arteries and abnormaly at exit of a stenosis (narrowing of the vessel.

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3
Q

Describe the profile of laminar flow.

A

Plug flow- blunt flow profile: happens when the flow adjust to changes in the vessel diameter.

Parabolic flow- is the result of friction on the blood with the blood cells traveling closer to the wall being slower and the cells traveling in the center traveling faster

both types are normal

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4
Q

What effects does stenosis have on blood flow?

A

Entrance effect- velosity ⬇️ to, pressure⬆️ because of the slow down cells are backing up like in a trafic jam

With in stenosis flowing through narrowing Velocity ⬆️⬆️ and presure ⬇️

Exit effect- ⬇️⬇️velocity ⬇️ pressure because of ⬇️ in volume

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5
Q

What are some clues to abnormal turbulent flow and what is the main organ system that is associated with pathology when it is present?

A

Murmur/ bruit (audible abnormal sound with heart beat)

Thill- vibrations of the muscle (palpable turbulent flow)

Most often associated with the cardiovascular system.

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6
Q

What is Reynold’s #?

A

It is a predictor of turbulent flow, it is a ratio between inerial (density, vessel diameter, blood velocity) and viscous forces (resistance of blood flow).

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7
Q

What are the spesific Reynold’s # to indicate weather or not there is Turbulant flow?

A

⬆️ # ⬆️ turbulance- >2000 = turbulence
1500-2000 = intermediet
> 1500 = laminar flow

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8
Q

What causes blood flow?

A

Changes in energy (not just pressure). Energy gradient come from many sources.

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9
Q

Name the types of energy that has their effect on blood flow.

A
  • Kinetic energy -Pressure

- Gravitational energy

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10
Q

What causes the loss of energy in blood flow?

A

Viscous loss- resistance of flow

Friction loss- friction caused by the walls of the vessels

Inertial loss- changes in flow velocity

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11
Q

What are the %s of viscosity of blood that are with in normal limits?

A
  • 45% WNL
  • 50% < = high viscosity
  • 40%> = low viscosity
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12
Q

What vessels causes the highest amount of friction?

A

Capillaries

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13
Q

What is Stenosis?

A

Narrowing of a vessel’s lumen, either due to plaque, thrombus or from compression of adjacent structures.

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14
Q

Assuming stiff walls what is thew formula to find the pressure with in a vessel?

A

Pressure = flow x resistance

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15
Q

What is and causes transmural Pressure and what are indications of how high or low it is?

A

The describes the pressure which acts on expanding the walls of veins , how much of a change depends on the change in volume or/and pressure:
High TP = round, overfilled viens
Mid TP = oblong, round shape, full vein
Low TP = dumbbell/variable shape, under-filled vein

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16
Q

What are the differensece of hydrostatic pressure in relation to where the vessel is on the body?

A

Pressure is low above the heart and and high below the heart.

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17
Q

Where are the changes with inspiration and expiration of respiration to blood flow, why is this importent and why is this so?

A

With out respiration blood can not flow back to the heart

Inhale- lungs expand and diaphragm moves inferiorly causing the pressure with in the thorax to ⬇️ abdominal pressure to ⬆️ so upper flow ⬆️ and lower limbe flow ⬇️

Exhale lungs deflate, diaphragm moves superiorly, pressure in thorasic ⬆️ and abdominal pressure ⬇️, alowing blood to flow from te lower limbs to the heart.

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18
Q

What is Doppler and a doppler shift?

A

The change in frequency or a moving object in relation to a stationary observer
The doppler shift is the change in frequency, also called doppler frequancy.
Doppler frequency = F reflected - F transmited

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19
Q

What does demodulation have to do with doppler?

A

Machine process it and separates the transmitted frequency from the doppler frequency.

20
Q

How does the transmitted frequency compare to Doppler F?

A

Tran. Fs= 2-12MHz Doppler Fs= 20Hz - 20kHz

21
Q

What is the Doppler equation?

A

F (doppler) = 2 x blood velocity x F(trans.) x cosø

C

22
Q

What are the # 2 constant doppler shifts represent in the equation (2)?

A
  1. During transmission- beam hits blood cells

2. During receptions- when beam is reflected back and received from transducer

23
Q

How is doppler shifts related to vvelocity?

A

They are directly proportioal

⬆️ blood velocity = ⬆️ doppler

Mechien calculates amount of shift into velocity (seen/heard with spectral doppler.

24
Q

How is Doppler shift related to transducer frequency?

A

Directly proportional

if theres trouble detecting flow increase frequency.

25
Q

What does the Cosine angle have to do with the doppler shift?

A

Well doppler shift is greeatest at 0 and 180 degrees (1 and -1), where beam is parallel to vessel

The doppler shift is undetectible at 90 degrees when the cosine is 0 and the beam is perpendicular to the wall
US requires a cosine of 120 degrees (cosine value of 0.5<)

26
Q

How is the doppler shift related to propagational speed?

A

Inversely

27
Q

What is non-directional doppler?

A

This is the POWER Doppler, it is sensitive to any shift but can not display direction or velocity of flow. So it is used assessing doppler shifts only.
it does not have to deal with aliasing and not as needy for a correct angle

28
Q

What is Bidirectional flow?

A

This is our COLOR Doppler.

it can tell the direction, and average velocities of flow and is used on every pathology found, as well as PVs, HV, Ovaries, Testis, Renals, OB

in the color box turbulance can be detected with the mixing of colors

29
Q

Autocoralation?

A

Processing technique used in color doppler, fast but not accurite in evaluating doppler shifts and translate them in to mean velocities and displays the appropriate color, processing larg amounts of information quickly

30
Q

What are color packets sizes and what are there pros and cons?

A

Multiple pulses fired into color box area, number of pulses fired called packet or ensemble

Large Packet Pros-
Accurate measure of velocity
Sensitive to low flow

Large Packet Cons-
Longer frame time
Reduced frame rate
Decreased temporal resolution
When you are your own sonographer…
31
Q

What is Spectral doppler?

A

Graphic and audio representation of velocities in one area over time

32
Q

What does the phase quadrature do?

A

Phase quadrature responsible for ordering timing of signals and translation from doppler shift to appropriate velocity.

33
Q

What are ways Spectral doppler be abjusted?

A

Can adjust the velocity/PRF to optimize spectral graph
Can also adjust gain/greyscale
-Fast Fournier Transform
-Brightness represents amount of blood cells at a specific velocity
-Gain affects background/waveform brightness

34
Q

What are the advantages of spectral doppler?

A

Displays individual velocities
Bright = many blood cells at that velocity
Dim = few blood cells at that velocity
Very accurate
Can use characteristics of spectral waveform to identify turbulence (pathology)
Spectral Broadening

35
Q

What is the spectral window?

A

Spectral Window- area between baseline and displayed velocity
Vessel Resistance

36
Q

What is CW Doppler and its pros?

A 
Continuous Wave- spectral only no image
	-Great for high velocities (heart)
	-Range Ambiguity (no image/depth info)
Similar to M-Mode- measure velocities down one line of data
2 crystals- 1 “ON”, 1 “OFF”
Higher sensitivity
	-CW- able to detect subtle doppler shifts
	-PW- subtle echoes become noise
37
Q

What is PW (Pulsed wave) Doppler?

A

this is what we mainly use.

One crystal used for doppler purposes
Alternates between “ON” time and “OFF” time
Sonographer adjusts gate location
Machine uses time delay to determine echo depth
	-13usec/cm
Range Specificity
Inaccurate at high velocities
	-Aliasing!
38
Q

What is Aliasing?

A

Occurs when velocities are higher than the doppler settings are adjusted to
Can have velocities that “max out” our probes/software
Appears as color mosaic on color doppler, color bar “wrapping”
Appears “wrapped around” graph on spectral doppler

39
Q

What is the Nyquist Limit?

A

Nyquist Limit- determines highest velocity we can evaluate without aliasing
depends on PRF
Only factor effecting PRF if depth.

40
Q

What is the Nyquist equation?

A

NyL Hz = PRF Hz

2

41
Q

What is the relationship between Aliasing and velosities?

A

directly proportional

42
Q

What is the relationship between Aliasing and depth?

A

depth is inversly related to PRF so

⬆️depth = ⬇️PRF = ⬆️ likely hood of aliasing

43
Q

What is the relationship between aliasing and transducer frequency?

A

Directly; ⬆️ Tr F = ⬆️aliasing

44
Q

How do you adjust for Aliasing?

A
  • Increase PRF
  • Decrease transmitted Doppler F
  • Decrease distance to ROI
  • Use CW
  • Decrease Baseline (Doesn’t alter PRF, adjusts graph only)
45
Q

Name, define and consider a way to remedy doppler artifacts.

A

Clutter- appears as irregular velocities along spectral graph
Ghost Artifacts- “fill in” of color on non-vascular areas
~Can remedy these by adjusting wall filter
Crosstalk/Mirror Artifact- appears as identical spectral wave opposite to actual spectral wave
~Can remedy this decreasing spectral gain or decreasing scan angle.

46
Q

Define a wall filtter.

A

Used to eliminate low frequency doppler shifts (Tissue/bowel movement)
Appear as black area above and below baseline on spectral graph

47
Q

What is the resistive index ratio?

A

Resistivity Index- ratio that determines arterial resistance
Arterial Stenosis, transplant applications

	RI   =   Velocity max  -  Velocity min
			               Velocity max
48
Q

What is the Pulsatility Index?

A

Pulsatility Index- measures the variability of velocities within a vessel
Obstetrical and transplant applications

PI = Velocity max - Velocity min

			               Velocity mean

Ultrasound Physics (6 decks)

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