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Vascular 1 > SVT Day > Flashcards

SVT Day Flashcards

1
Q

What is acoustic impedance measures in?

A

Rayls or Pa per cm

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2
Q

What is the equation for acoustic impedance/

A

Z = pc

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3
Q

What is the intensity reflection coefficient?

A

Intensity reflected / Intensity incident
- the bigger the difference, the more reflection

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4
Q

Why does bone cause dropout?

A

Bone has a very high acoustic impedance compared to soft tissue

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5
Q

What is a specular reflection?

A

Reflection at a smooth, straight boundary

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6
Q

What is Rayleigh scattering?

A

Occurs with reflectors much smaller than the ultrasound wavelength
- can cause speckle in B-mode

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7
Q

Why is Rayleigh scattering useful for Doppler?

A

We do not normally scan at 90 degrees in Doppler

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8
Q

Why is the sky blue?

A

Short wavelength blue light gets scattered more than longer wavelengths

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9
Q

What is Snells law?

A

The law of refraction
sine(theta2) / sine(theta1) = c2 / c1

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10
Q

What causes attenuation?

A

absorption, scattering, reflection, refraction, beam divergence

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11
Q

What are the units for attenuation?

A

dB / cm / Mhz

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12
Q

How is axial resolution calculated?

A

Axial resolution = 1/2 pulse length

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13
Q

What is Huygen’s Principle?

A

Array transducers use multiple piezoelectric elements and combine multiple elements to form the ultrasound beam

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14
Q

Why do superficial structures sometimes appear difficult to see?

A

The are too close for interference and focussing of the beam

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15
Q

What is cavitation?

A

Ultrasound pressure waves can push fluid out the way - causes rarefaction and expansion.
- can cause tiny microbubbles which can then burst and release energy as heat
- can damage surrounding objects

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16
Q

How can you minimize cavitation?

A

Reduce MI

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17
Q

What is Ti?

A

The ratio of total acoustic power to the power needed to raise 1kg of tissue by 1 degree

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18
Q

What are the different ways of measuring ultrasound beam intensity?

A
  1. Spatial peak, temporal average
  2. Spatial average, temporal average
  3. Spatial average, temporal peak
  4. Spatial peak, temporal peak
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19
Q

What is the Doppler angle?

A

The angle between the direction of flow and the transducer lens

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20
Q

Why does aliasing occur due to vessel tortuousity?

A

Angle becomes closer to zero, so causes a greater Doppler shift

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21
Q

What can strong side lobes do?

A

Degrade lateral resolution

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22
Q

What is apodization?

A

Strength of transducer signal becomes weaker towards edges of transducer - to reduce side lobes

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23
Q

What are two advantages of using arrays?

A
  1. They enable electronic beam steering
  2. They enable electronic beam focusing
24
Q

How is electronic focussing achieved?

A

By introducing time delays in pulse excitation of different elements

25
Q

How is receive focus achieved?

A

By introducing time delays of different durations to the individual signals so the signals will be in-phase when summed

26
Q

What is frame rate dependent on?

A

Colour line density
Width and depth of colour box
Number of pulses per length (Ensemble length or packet size)
PRF

27
Q

What is flow?

A

Q = mean velocity * Area

28
Q

How does the total XSA change as arteries branch?

A

It increases

29
Q

What is a Newtonian fluid?

A

Uniform

30
Q

What is haematocrit?

A

The percentage of blood occupied by RBCs

31
Q

What are laminae?

A

The layers of fluid in blood

32
Q

What does laminar mean?

A

Layers of blood moving over each other

33
Q

What is Pouseilles Law?

A

Q = change in pressure / Resistance

Q = (change in P * Pi * r**4) / 8 u L

34
Q

How does resistance add in series?

A

Sums normally

35
Q

How does resistance add in parallel?

A

1/Rt = 1/R1 + 1/R2 ….

36
Q

What causes reflections of pulse waves?

A

Changes in impedance e.g. branches

37
Q

What happens to pulse wave if there is a distal occlusion?

A

There is a total reflection of pressure = waveforms with no net flow
- High resistance waveform

38
Q

What happens to CFA flow during exercise?

A

There is higher diastolic flow as distal arteries have dilated

39
Q

What are entrance effects?

A

When there is a change in area, there is a change in flow profile e.g. more plug-like in a stenosis

40
Q

What is shear of the velocity profile?

A

The change in velocity across the velocity profile

41
Q

What does low shear cause?

A

Thrombosis

42
Q

How does curvature change flow?

A

In laminar, fastest flow will be towards outer wall of the curve
In blunt flow, is opposite

43
Q

What are the 3 components of energy in blood?

A
  1. Pressure energy
  2. Gravitational energy
  3. Kinetic energy (velocity)
44
Q

What is boundary layer circulation?

A

Recirculation of flow due to changes (increases) in area e.g. carotid bulb or post-stenotic dilatation

45
Q

When should you measure velocities in the carotid bulb?

A

Never, unless stenosis within

46
Q

What happens to mean and peak velocity in stenosis?

A

Mean velocity will increase
Peak velocity might not increase until stenosis becomes more severe

47
Q

What are viscous losses?

A

Loss of energy due to friction

48
Q

What type of losses are entrance and exit losses?

A

Inertial losses

49
Q

How do plaques ulcerate?

A

Pressure differences can cause forces across the plaque

50
Q

What is pressure drop proportional to?

A

Velocity

51
Q

Is pressure loss greater in systole or diastole?

A

Systole (higher velocity)

52
Q

What can a damped waveform indicate?

A

Proximal disease

53
Q
A
53
Q
A
54
Q
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55
Q
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56
Q
A

Vascular 1 (5 decks)

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