Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Vascular 1 > Canvas Chapter Notes > Flashcards

Canvas Chapter Notes Flashcards

1
Q

Define a sound wave?

A

A longitudinal pressure wave travelling at the speed of sound through a medium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Define pressure?

A

The force exerted from the excess density of molecules above or below the mean density of the medium as molecules get squashed and pulled apart

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is phase of a wave?

A

A point along the course of one period of the wave expressed as an angle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the pulse envelope?

A

The characteristic shape of the pulse, created by drawing a line through successive peaks and rarefactions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a spectrum?

A

A plot of magnitude against frequency (or time)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does the spectrum of a sine wave look like?

A

A single vertical line (only 1 frequency)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does an indefinitesimally short pulse look like for a) Time Domain and b) frequency domain spectrums?

A

Time domain = single vertical line
Frequency domain = horizontal line

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the bandwidth of an infinitely short pulse?

A

Infinite bandwidth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What happens to bandwidth as pulse length increases?

A

Bandwidth decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How does elasticity relate to stiffness?

A

Elasticity = 1 / stiffness

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Do materials generally differ more in density or stiffness?

A

Stiffness - therefore stiffness is a better guide to predicting speed of sound than density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How do you calculate speed of sound in a material?

A

c = Sqrt( k / p)
k = stiffness
p = density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is characteristic impedance?

A

The response of molecules in a medium to the excess pressure in the wave (assuming a simple plane wave)
- it is a measure of how fast a molecule in a medium moves in response to the excess pressure of the sound wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How is acoustic impedance related to energy loss?

A

It is not

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is intensity of ultrasound?

A

Power per unit area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the frequency domain spectrum of a) short pulse b) long pulse

A

a) a wider bell-shaped curve
b) a narrow bell-shaped curve

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the relationship between time domain and frequency domain?

A

They are reciprocal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What determines the size of an echo at an interface?

A

Differences in characteristic impedance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is power?

A

The rate at which energy is transferred

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is intensity?

A

Power per unit area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is specular reflection?

A

Reflection at a plane interface between two tissues with different acoustic impedance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

When does Rayleigh scattering occur?

A

When sound encounters microscopic structures much smaller than a wavelength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is a coherent imaging technique?

A

Where the phase of the waves may be fully specified at each point in space
- lasers and ultrasound are coherent techniques
- light bulbs are not

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What do coherent imaging techniques give rise to?

A

Speckle patterns

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is attenuation?

A

The process by which intensity of a wave or pulse decreases with distance from the source
- equivalent to resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What are boundary losses?

A

Energy reflected away from the beam at interfaces (specular reflection)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What are the 3 mechanisms that give rise to attenuation?

A
  1. Absorption - conversion of sound to heat
  2. Scattering - energy diverted out of the beam
  3. Beam divergence - depends on beam shape = spreading out
    (not strictly attenuation)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

How does attenuation increase with depth?

A

It increases exponentially

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

How does frequency impact attenuation?

A

High frequencies are absorbed and scattered more

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is a point source?

A

A sound wave source that is much smaller than a wavelength of sound
- it spreads out in all directions
- e.g. when you speak, the wavelength is bigger than the size of your mouth - sound spreads out in all directions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What are plane parallel waves?

A

Waves that only propagate in one direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is the Fresnel Zone?

A

The Near zone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What is the equation for Fresnel Zone length?

A

D = a**2 / wavelength

D = length
a = half aperture width

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is the Fraunhoffer Zone?

A

The far field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What is the equationfor spread in the beam in the far field?

A

sin(theta) = wavelength / a
a = half aperture width
theta = half the angle of spread
For a square transducer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What is the effect of a large aperture for a given wavelength?

A

Uniform beam with long near field and small spread in the far field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What is the last axial maximum?

A

The last central intensity peak within the near field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

What are Huygens sources?

A

Many point sources next to each other - acts as a straight beam at the centre but beams diverge at the edges

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What is the unit and symbol for bulk modulus / stiffness?

A

Pascals (Pa) and Kappa (K)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

How does speed of sound relate to density and stiffness?

A

c = Sqrt(K / p)
K = stiffness
p = density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

How does greater density impact speed of sound?

A

Increased density decreases speed of sound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

What is the percentage reflected intensity at soft tissue - soft tissue boundary?

A

1% or less

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q
A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What is the percentage reflected intensity at bone - soft tissue boundary?

A

50%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What is the equation for refraction?

A

Sin(theta2) / Sin(theta1) = c2 / c1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What is the reflection coefficient and symbol?

A

Z, is the relative intensity of sound that is reflected at a boundary

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What does the angle of refraction depend upon?

A

Angle of incidence and speed of sound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What is the percentage reflected intensity at air - soft tissue boundary?

A

100%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

When does Rayleigh scattering occur?

A

When target size &laquo_space;wavelength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What 2 factors impact ISB?

A
  1. Pulse length
  2. Doppler angle
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

How does frequency of sound relate to scattering and absorption?

A

Higher frequency = higher scattering and higher scattering = higher attenuation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

What is the resonant frequency of a PZT transducer?

A

The frequency at which it vibrates when a voltage is applied across it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

Why is damping of transducers needed?

A

To create short pulses to give good resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

What is the purpose of transducer matching layers?

A

There is a large impedance difference between the hard, rigid PZT and soft body tissue - so transmitted intensity will be low
- matching layer enables sound to be transmitted into the body more efficiently

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What are general properties of matching layers

A
  1. Impedance between PZT and the body
  2. 1/4 of a wavelength thick
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

Why are matching layers 1/4 of a wavelength thick?

A

The wave reflected at the body interface will have its phase inverted - by having 2 * 1/4 wavelength, the wave will then be reflected by the matching layer in-phase and will superposition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

Why do transducers use multiple matching layers?

A

Each layer has an impedance of the geometric mean of those on either side
- this allows matching over a wider range of frequencies as contained in a short pulse of sound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

What are advantages of wide-bandwidth transducers?

A
  1. Short pulses = good spatial resolution
  2. Potential for complex pulse shapes
  3. Harmonic imaging at higher frequencies possible
  4. The same transducer can use different frequencies for imaging and Doppler
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

What characteristics make a good wideband transducer?

(4 reasons)

A
  1. Good damping in the backing layer
  2. Very good matching to body impedance
  3. PZT thickness chosen for middle of the wideband range
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

What causes spread in the elevation scan plane?

A

Beam width - side lobes present in elevation and scan plane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

How many dimensions does a basic linear array have?

A

1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

What is a 1.5D array?

A

The transducer element is divided into 3 in the elevation plane
- this can improve image quality

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

Why do multiple focal zones reduce frame rate?

A

Each focus requires a separate transmitted pulse - frame rate doubles with 2 focal zones and triples with 3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

What is receive focus?

A

The receiving shape for echoes coming from different ranges
-is implemented by introducing a receive delay to particular transducer elements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

What happens to the shape of the received wave as we add more harmonics?

A

It gets closer to square in shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

What characteristics of waveforms indicate it is composed of higher harmonics?

A

Sharply rising/falling edges

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

What is non-linear propagation?

A

The concept that the speed of sound at peak pressure is slightly higher than the speed of sound at rarefaction
- peaks more faster than troughs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
62
Q

Why does harmonic imaging give better resolution?

A

Higher frequency gives better resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
63
Q

What are the two ways we can use harmonic information to form an image?

A
  1. Using a filter method - remove transmit frequency from the received signal = shorter received pulse
  2. Pulse inversion method - requires 2 transmit pulses of opposite phase transmitted in sequence. The echoes from the pulse are added together

Improves signal to noise ratio of b-mode and reduces side lobe artefacts and reverberation are reduced

Improves contrast resolution when on

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
64
Q

What are the pros and cons of harmonic imaging?

A

Pros: - better resolution at higher frequency
- removes clutter from the image

Cons: - weaker echoes at 2nd harmonic so penetration is poorer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
65
Q

How are harmonics used in practice?

A

A combination of second and first harmonics to give overall improvements of image quality without losing penetration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
66
Q

How are modern scanners adaptable?

A

They can:
- alter the transmit shape
- change the transmit power
- change the timing of pulses
- change the aperture used

These factors can be changed between each pulse - no two pulses need be the same

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
67
Q

What does the adaptability of pulses allow?

A
  1. Dynamic multi-zone focusing
  2. Steering
  3. Coded excitation to improve signal to noise ratio of weak signals
  4. Control of pulse phase, for harmonic imaging
  5. Mixed B-mode and Doppler imaging
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
68
Q

What is the beam former?

A

It controls exactly what pulse: shape, timing and phase are produced by each element in the transducer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
69
Q

What are typical PRFs?

A

1000’s per seconds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
70
Q

Why is TGC needed?

A

Attenuation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
71
Q

What is analogue to digital conversion?

A

Converts the analogue amplitude of a returning echo signal to the nearest integer value at set time intervals (bins) - this is then stored as a sequence of numbers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
72
Q

What are the advantages of digitising?

A
  1. No further risk of introducing noise or distortion into the signal
  2. Powerful computing can be done = image processing
  3. Easy storage in memory
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
73
Q

How are raw echoes turned into images

A

ADC - analogue digital conversion
- often done by digitizing the r.f signal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
74
Q

What is echo signal rectification?

A

Turning the signal all positive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
75
Q

What is envelope detection?

A

Rectification and low pass filtering together

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
76
Q

How are the dynamic ranges of echoes fitted into the range of the display monitor?

A

Grey scale mapping / compression

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
77
Q

How can non-linear amplification improve image quality?

A

It can enhance the echoes of interest e.g. low level echoes or mid range echoes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
78
Q

What is compound scanning?

A

When multiple beams are sent out at different angles = allows more sides of objects to be perpendicular to the beam

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
79
Q

What are the 4 main assumptions of ultrasound imaging?

A
  1. The speed of sound is constant in the body
  2. Attenuation in tissue is constant
  3. The beam axis is straight throughout the range of the beam
  4. The ultrasound beam is indefinitely thin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
80
Q

When do artefacts occur?

A

When the assumptions of ultrasound are not met

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
81
Q

What are examples of speed of sound artefacts?

A
  1. Refraction - causes image distortion
  2. Axial misplacement
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
82
Q

What are examples of attenuation artefacts?

A
  1. Poorly adjusted TCG
  2. Acoustic shadowing
  3. Post-cystic enhancement
  4. Poor skin contact
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
83
Q

What are some examples of reflection artefacts?

A
  1. Mirror Image artefacts
  2. Reverberation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
84
Q

What are some examples of beam shape artefacts?

A

Slice thickness artefact

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
85
Q

What is the approximate temporal resolution of the human eye?

A

25 fps

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
86
Q

What two factors determine frame rate?

A
  1. The number of ultrasound lines / beams
  2. Depth of image
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
87
Q

What is reverberation?

A

Multiple reflection between parallel surfaces

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
88
Q

What is contrast resolution?

A

The ability to detect one target against another

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
89
Q

What is the Doppler shift?

A

The change in frequency between the transmitted and received soundwaves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
90
Q

Why is there the factor of 2 in the Doppler equation?

A

There have been 2 Doppler shifts: one on the way out and one on the way back

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
91
Q

What is one assumption of the Doppler effect?

A

The target velocity is much smaller than the speed of sound in tissue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
92
Q

How does sign of velocity change in the Doppler equation?

A

v is positive for targets moving towards the transducer and negative for targets moving away

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
93
Q

What is the cross-over region of a CW transducer?

A

The sensitive region where transmit and receive beams cross over

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
94
Q

What produces high and low Doppler frequencies?

A

High - flow towards transducer
Low - flow away from the transducer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
95
Q

What algorithm converts from time domain to the frequency domain?

A

Fourier Transform

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
96
Q

How do velocity profiles of slow and fast moving blood differ?

A

Slow - parabolic flow
Fast - plug flow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
97
Q

What is an advantage of CW doppler?

A

It can detect very high velocities with no aliasing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
98
Q

What is high PRF mode?

A

It doubles the PRF and Nyquist limit by creating 2 sample volumes - one at half target depth = can be problematic if there is a vessel here

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
99
Q

Why are PW Doppler pulses generally longer (6-7 cycles) than B-mode?

A

The transmit frequency needs to be well defined in order to accurately detect changes due to moving targets

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
100
Q

Why do shorter Doppler pulses (i.e. to look at narrow regions of vessels) causes Doppler frequencies to be less well defined?

A

Intrinsic spectral broadening (ISB)
- multiple Doppler shifts from varying velocities of blood
- is intrinsic to the machine and cannot be avoided

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
101
Q

What is the impact of a highly focused beam on PW spectrum?

A

The same as a short pulse - ISB
Targets moving across the beam will give Doppler signal whose amplitude rapidly increases and then decreases as target moves across the beam
- Rapidly changing signals produce wide spectrums in the frequency domain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
102
Q

How much can ISB impact velocities?

A

+/- 10%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
103
Q

Why is an ideal Doppler angle of 45 - 60 degrees used in practice?

A

< 45 can lead to poor penetration in practice

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
104
Q

What is pulsatility index (PI)?

A

Measure of how pulsatile a waveform is - high for pulsatile, low for damped or resistive
PI = (PSV - EDV) / average of peak envelope

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
105
Q

What is resistive index (RI)?

A

Measure of ratio of EDV to PSV
- High EDV indicates low resistance and gives low RI value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
106
Q

When does waveform ghosting / spectral trace reflection occur?

A

In very superficial vessels e.g. ankle vessels
- may also occur if the gain is too high

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
107
Q

How can weak PW signals be amplified?

A

Reduce the steer of the beam and heel-toe the probe

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
108
Q

What is the difference between side lobes and grating lobes?

A

Grating lobes are a special type of side lobe
They are both caused by the spreading out of energy from the main beam that is reflected back
- Grating lobes generally have larger amplitudes than side lobes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
109
Q

Does all of the energy stay within the main transducer beam?

A

No

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
110
Q

How do grating lobes appear?

A

At the wrong location but in the same direction as the main ultrasound beam

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
111
Q

How can you practically adjust for attenuation?

A

Adjust TGC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
112
Q

How can you correct for edge dropout practically?

A

Turn on CT scanning or compound scanning or heel-toe the probe

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
113
Q

When do comet tail artefacts occur?

A

When there is reflection between 2 very closely spaced reflectors - usually between metallic objects

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
114
Q

What is a resonance/ring down artefact?

A

Used in CEUS - vibration of very small structure e.g. gas bubbles - highly echogenic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
115
Q

What is phase aberration artefact and what may cause it?

A

It is the same as smearing vaseline on the lens and can be caused by a layer of subcutaneous fat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
116
Q

How can you reduce mis-registration/distortion/phase aberration artefacts in obese patients?

A

Turn of CT and compound scanning. Turning on tissue harmonic imaging might help

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
117
Q

What artefact may cause twin-image artefacts e.g. of aorta?

A

Refraction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
118
Q

How can refraction artefacts be overcome?

A

Changing the beam angle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
119
Q

What are the 3 main ways to reduce aliasing?

A
  1. Adjust scale
  2. Decrease depth
  3. Use a lower frequency probe
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
120
Q

How can motion artefacts appearon a spectral trace?

A

As bright chunks of spectral near the baseline

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
121
Q

What does each colour pixel show?

A

The mean frequency shift/velocity in that area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
122
Q

How many transmission pulses are needed for each colour line?

A

7 - 10

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
123
Q

What impacts frame rate?

A

Length and width of colour box and line density and depth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
124
Q

How is lateral resolution calculated?

A

LR = beam width / 2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
125
Q

What is the equation for beam width?

A

Beam width = wavelength x focal length / aperture size

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
126
Q

How is pulse length calculated?

A

PL = n x wavelength
n = number of cycles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
127
Q

What is greyscale mapping?

A

Converts the huge range of echo intensities from reflected tissue into 128 or 256 grey scale bins
- can be done in a linear, curved or sigmoidal manner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
128
Q

Do colour or B-mode pulses have wider bandwidth?

A

B-mode as they have shorter pulses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
129
Q

When do we see display monitor flicker?

A

When the frame rate is reduced below 25Hz

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
130
Q

What is the difference between frame rate and temporal resolution?

A

Frame rate is the number of frames displayed per second.
Temporal resolution is the ability to CAPTURE motion, does not involve the processing and display

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
131
Q

What is the grey level of a spectral waveform?

A

The number of RBCs that reflect that particular velocity or frequency shift

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
132
Q

How does sample volume impact frequency resolution?

A

Wide SV: long pulse, narrow bandwidth, better frequency resolution
Narrow SV: short pulse, wide bandwidth, worse frequency resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
133
Q

What can a small sample volume cause?

A

Intrinsic Spectral Broadening (ISB)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
134
Q

What is dynamic range?

A

The ratio of highest to lowest echo strength (voltage)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
135
Q

What does persistence do?

A

Sends multiple pulses and averages frames - temporal resolution may be an issue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
136
Q

What is autocorrelation?

A

The processing of a colour image that converts the spectrum of frequency shifts at each point to one value at output

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
137
Q

How does autocorrelation work?

A

It compares the phase from the speckle pattern produced by the ultrasound pulses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
138
Q

Does size or depth of a colour box have a bigger impact on frame rate?

A

Box size

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
139
Q

How can THI improve resolution?

A

It can improve contrast resolution
- reduces speckle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
140
Q

Why does post-cystic enhancement occur?

A

The ultrasound machine assumes for constant attenuation. There is very little attenuation in fluid - hence there is over-compensation post-cyst

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
141
Q

What is Reynold’s number?

A

A number that describes when turbulence will occur

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
142
Q

Above which Reynold’s numbers will there be turbulence?

A

> 2000 - 2500

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
143
Q

Explain Poiseuille’s law in words?

A

Resistance to flow depends on the geometry (mainly radius) and viscosity

And a pressure difference will cause fluid to flow in a steady manner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
144
Q

Explain the Bernoulli equation in words?

A

Energy is conserved - there is no perpetual motion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
145
Q

What is the unit for viscosity (u)?

A

Pascal seconds (Pa s)
or Kg m-1 s-1

146
Q

Does Reynold’s number have units?

A

No - it is a ratio

147
Q

What are the units for pressure?

A

Pa
Pascals

148
Q

What is the SI unit for energy?

A

Joules J

149
Q

What does viscosity depend on?

A

The temperature and haematocrit of blood

150
Q

What is the impact of temperature on blood viscosity?

A

Decreased temperature causes increased viscosity

151
Q

What is density?

A

Mass / volume

152
Q

What are the 3 causes of inertial losses?

A
  1. Acceleration
  2. Deceleration
  3. Change of direction
153
Q

What is the largest site of reflection in the arterial tree?

A

The arterioles

154
Q

What is Anisotropy?

A

The phenomena of attenuation (or other properties such as speckle pattern) varying depending on the orientation of the target to the ultrasound beam or image plane

155
Q

Why do short pulses have a range of frequencies centering around fmid?

A

Other frequencies are produced as the wave starts/stops

156
Q

What gives approximate bandwidth of a pulse?

A

Bandwidth = +/- 2 x 1/pulse length

157
Q

What is the equation for bulk modulus? (K)
regarding pressure and volume

A

K = -V (change in P / change in V)

  • note the minus sign occurs because the volume decreases with an increase in pressure
158
Q

How does speed of sound in a material relate to bulk modulus?

A

c = Sqrt ( K / p)

159
Q

Describe characteristic acoustic impedance?

A

The quantity for how easily a molecule in a medium moves in response to a given change in acoustic pressure

  • It is NOT resistance to a sound wave
160
Q

What is the equation for acoustic impedance at a molecular level?

A

Z = Excess pressure / Particle velocity

161
Q

What is the equation for Z in a material?

A

Z = Sqrt ( p K)

162
Q

What does the total scattered power of a target depend upon?

A
  1. Target size (area) - to the power of 6
  2. Frequency - to the power of 4
163
Q

What is superposition?

A

Waves in phase adding together

164
Q

How do absorption and scattering change with frequency?

A

Low frequencies are attenuated more (90%) than scattered (10%) energy loss
- high frequencies are absorbed and scattered more = poor penetration

165
Q

How do you narrow the beam for a transducer with a narrow aperture?

A

Increase the frequency

166
Q

What is the beam profile for a large aperture for a given wavelength?

A

Uniform beam with long near field and small spread in the far field

167
Q

What is dynamic range?

A

The difference in signal strength between the weakest and strongest echo

168
Q

What is interpolation?

A

Using a smaller number of scan lines to improve frame rate
- the gaps between lines are filled by synthetic data

169
Q

What are twinkle artefacts?

A

Artefacts arising from calcified vessels or stones

170
Q

How is an ultrasound image constructed?

A

Echoes are generated from reflection and scattering from irregularities in tissue (changes in acoustic impedance)

171
Q

What 2 key pieces of information are needed to display an echoes position?

A
  1. The range (distance) of the target from the transducer
  2. The direction of the target from the transducer - i.e. the position and orientation of the ultrasound beam
172
Q

What is a wave?

A

The transfer of energy due to local displacement of particle (but no net movement)

173
Q

Are shear waves longitudinal or transverse waves?

A

Transverse waves

174
Q

What is phase and its units?

A

The position within a cycle of oscillation
- measured in degrees

175
Q

How does pressure change when a medium is compressed?

A

It increases in the positive direction

176
Q

What is the excess pressure?

A

The difference between actual pressure and mean ambient pressure

177
Q

What is peak excess pressure?

A

The amplitude of a wave

178
Q

How is stiffness calculated?

A

The ratio of stress to strain

179
Q

What is stress or pressure?

A

The force per unit area

180
Q

What is strain?

A

The fractional change in thickness

181
Q

What are the units of strain?

A

No units, is a ratio

182
Q

What are the units of stiffness?

A

Pascals
K = stress / stiffness
= Pa / no units

183
Q

What are the units of stress?

A

Pascals (N/m*2)

184
Q

Why is speed of sound faster in bone than tissue, even if it is twice as dense?

A

It has a stiffness 10x greater

185
Q

What is the equation for acoustic impedance (Z) relating to local particles?

A

Z = P / v
- P = LOCAL pressure
- V = LOCAL particle velocity

186
Q

What is acoustic impedance analogous to?

A

Electrical Impedance

187
Q

What is the general acoustic impedance of a material given by?

A

z = Sqrt(pk)
- acoustic impedance increases with both density and stiffness

also

z = pc

188
Q

How does acoustic impedance change with a) stiffness b) density?

A

Increases in both density and stiffness will cause an increase in acoustic impedance

189
Q

How does total particle pressure and total particle velocity change across an interface of changing acoustic impedance?

A

Total particle pressure and total particle velocity must be continuous

190
Q

How much reflection occurs at soft tissue-soft tissue interfaces?

A

~1%

191
Q

What percentage reflection occurs at soft tissue - fat interface?

A

~10%

192
Q

What percentage reflection occurs at soft tissue - air boundary?

A

99.9%

193
Q

How does frequency impact reflection coefficient?

A

It does not

194
Q

What is diffuse reflection?

A

The reflection at a rough interface where ultrasound is scattered reflected.

195
Q

What transducer properties cause diffraction of waves?

A

An aperture smaller than the wavelength

196
Q

What is the equation for NFL?

A

NFL = a^2/wavelength

197
Q

What is non-linear propagation?

A

The theory that high-pressure (compressions) areas of the wave propagate faster than rarefactions
- rarefactions start to catch up with compressions
- compressions become taller and narrower and rarefactions become lower in amplitude and longer

198
Q

How do harmonics of short pulses appear?

A

They appear as repeats of the pulse spectrum around the fundamental frequency, rather than narrow spectral lines

199
Q

What happens to the shape of a pulse as it travels further into a medium?

A

As the pulse travels further, higher frequency components are attenuated more rapidly than low-frequency components and the pulse shape becomes more rounded as the overall amplitude is reduced.

200
Q

How does harmonic imaging work?

A

The fundamental frequency is ignored and only forms images using the second harmonic part of the pulse
- the ultrasound beam is narrower and suppresses artefacts such as side lobes
- Can use: 1. Pulse inversion method or 2. High-pass frequency filter

201
Q

How does scattering relate to angle of incidence?

A

It is independent of angle of incidence

202
Q

What is specular reflection?

A

Reflection at a smooth, mirror-like surface

203
Q

What does reflection at an interface depend on?

A

Mismatches in:
1. Acoustic impedance
2. Density
3. Speed of sound

204
Q

What is non-linear propagation concerned with? (2 reasons)

A
  1. Steepening in the shape of the ultrasound pulse
  2. Generation of harmonics at multiples of the fundamental frequency
205
Q

What does DICOM stand for?

A

Digital imaging and Communications in Medicine

206
Q

What is DICOM?

A

A set of protocols of how to do/manage various operations and formats relating to medical imaging

207
Q

How does DICOM display different levels of brightness?

A

It uses the concept of just noticeable difference (JND) between luminance levels of the display

208
Q

How does DICOM use a Test Target to measure contrast detectability?

A

It uses a Test Target
- is a square image of 8 horizontal or vertical sinusoidal bands across the image
- for different background grey levels, the amplitude of the bands is adjusted and increased above the background level until you can just notice the bands

209
Q

What is the non-linear response of the human eye?

A

The human eye needs a greater range of contrast at low light levels in order to detect change than it does at high levels of illumination

210
Q

How does the DICOM scale overcome the non-linear response of the human eye?

A

It specifies a compensation curve for displays to give a ‘perpetually linearised’ image
- ensures contrast detectability within dark areas is the same as in the bright areas of the image

211
Q

What is the DICOM standard for colour display in ultrasound images?

A

There is currently no equivalent DICOM standard for colour images

212
Q

What are other external factors that may impact image quality?

A

Angle of viewing (e.g. oblique)
Background room lighting
Viewing distance

213
Q

How is energy carried by a wave related to amplitude?

A

Energy is proportional to amplitude squared
- intensity is also proportional to amplitude squared
- amplitude can also be thought of as pressure

214
Q

What is bandwidth?

A

Within a pulse, no two cycles are the same, unlike a pure Sine wave where every cycle is identical
- generally most of the pulse looks like a sine wave just at each end the amplitude falls to zero
- the spectrum has a bandwidth centred about a central frequency

215
Q

How is elasticity related to stiffness?

A

Elasticity = 1 / Stiffness

216
Q

Why are we more interested in intensity of ultrasound, not energy or power?

A

Energy is not transmitted equally in all directions
- we are more interested in power per unit area (intensity)

217
Q

What are the energy losses at boundaries?

A

There are none

218
Q

How does acoustic impedance relate to speed of sound?

A

Z = pc

219
Q

What is the equation for ratio of reflected intensity (Ir) to incident intensity (It)?

A

Ir / It = ((Z2 - Z1) / (Z2 - Z1))^2

220
Q

What is Poiseuille’s Equation?

A

Change in pressure = (8uLQ) / (Pi r^4)

221
Q

What is Poiseuille’s Equation?

A

Change in pressure = (8uLQ) / (Pi r^4)

222
Q

How does lowering frequency impact speckle pattern?

A

It makes it coarser

223
Q

What are boundary loses?

A

Energy reflected away from the beam at interfaces

224
Q

How is energy lost through absorption?

A

Sound energy is converted to heat - making molecules vibrate in a disordered and random way i.e. not coherent

225
Q

What are the units for attenuation coefficient/

A

dB cm-1 MHz-1

226
Q

Why can’t you image through bone?

A

50% of energy is reflected and the rest is quickly attenuated

227
Q

What is Snell’s Law?

A

n1 sin(theta1) = n2 sine(theta2)

228
Q

Why is a large pulse wave sample advantageous?

A

It reduces ISB

229
Q

What is TIC?

A

The thermal index for when the ultrasound is near bone and

230
Q

What are the 2 main classifications of ultrasound imaging hazards?

A

Thermal and non-thermal

231
Q

What are the two main types of thermal hazards?

A
  1. Tissue heating - can cause cell death
  2. Transducer self-heating - can cause erythema + burning
232
Q

What are the 2 main types of Non-thermal hazards?

A
  1. Radiation force - energy absorbed by tissue. This can cause streaming - the movement of particles
  2. Cavitation - oscillation of small gas bodies or bubbles
233
Q

What are the two types of cavitation?

A
  1. Stable Cavitation - causes microstreaming
  2. Collapse cavitation - can cause physical damage and free radicals
234
Q

What factors determine whether cavitation can occur?

A
  1. Are there free gas bodies - called cavitation nuclei
  2. The pulse shape and frequency of ultrasound
235
Q

What do thermal effects depend on?

A

The average energy input (or intensity) to the tissue

236
Q

What do cavitation effects depend on?

A

The amplitude and length of individual pulses and the presence of cavitation nuclei - gas bodies

237
Q

What causes bubble collapse during cavitation?

A

Magnitude of negative pressure experienced during rarefaction - influences likelihood of collapse
- the transition from large positive pressure to large negative pressure

238
Q

What is the FDA limit for scanner MI output?

A

1.9

239
Q

How does frequency impact MI?

A

Lower frequency increases MI

240
Q

What are the two distinct risks of using contrast agents in CEUS?

A
  1. Pharmacological risk - associated with injected substance
  2. Risk of physical effects - gas bodies being insonated in tissue
241
Q

What do potential bio-effects of CA depend upon?

A

Rarefactional pressure amplitude
Agent dose
Agent delivery
Imaging mode
Tissue properties
Clearing pulse - bursting bubbles

242
Q

How does energy relate to pressure?

A

Energy is proportional to pressure amplitude squared

243
Q

Why is energy carried by a sound wave always positive?

A

It is proportional to pressure amplitude squared

244
Q

What are some of the variables that are not ideal in terms of the haemodynamics of blood vessels?

A
  • branches and curves
  • flexible and distensible
  • Uneven multidimensional flow
  • gravity
  • feedback systems
  • assumes constant temperature
  • volume changes
245
Q

What is the equation for volume flow?

A

Q = v * A

246
Q

What is Poiseuille’s formula?

A

Change in P = (8* mean v * L * u) / r^2
in a rigid tube:
change in P = (8 * Q * L * u) / Pi * r^4

247
Q

What is Poiseuilles Law?

A

Change in P = 8QLu / Pi*r^4

248
Q

What is the formula for Reynolds number?

A

Re = p v L / u
Re = 2rpv/u
Is also the ratio of inertial to viscous losses

249
Q

What is viscosity?

A

The internal friction in a fluid

250
Q

What is polycythemia?

A

Too many RBCs, u increases

251
Q

How does dialysis impact viscosity?

A

RBCs can be smashed up, u decreases

252
Q

What are the 3 main forms of pressure within the circulation?

A
  1. Dynamic pressure - work done by heart contraction (120mmHg)
  2. Static pressure - residual, if dead. Generally small, 5-10mmHg
  3. Hydrostatic pressure - due to gravity
253
Q

What equation relates pressure and height?

A

P = -p g h
- note is negative because pressure decreases as h increases

254
Q

What is the equation for energy density (Bernouilli Equation)?

A

Energy density = P - pgh + 1/2 p v^2
OR, P - pgh + 1/2 p v^2 (before) = P - pgh + 1/2 p v^2 (after)

255
Q

How do velocity and pressure relate with the Bernouilli Equation?

A

If v increases, P decreases
If v decreases, P increases

256
Q

What are the 4 main causes of inertial losses?

A
  1. High flow rates
  2. Changes in diameter
  3. Sharp changes in direction
  4. Angles
257
Q

What are streamlines?

A

Lines drawn tangent to the direction of flow

258
Q

Which vessels are physiologically effected by hydrostatic pressure?

A

Arteries and veins

259
Q

T/F: There are no inertial losses in a straight tube with constant flow

A

F

260
Q

T/F: In laminar flow, the boundary vessel extends throughout the vessel

A

T

261
Q

T/F In laminar flow, there is no flow just next to the vessel wall

A

T

262
Q

T/F In plug flow, there is no flow just next to the vessel wall

A

T

263
Q

Which arteries are most likely to experience turbulence?

A

Large arteries with high flow velocities e.g. aorta

264
Q

Are we likely to get plaque build up at high or low shear surfaces?

A

Both - bifurcations are the most common site

265
Q

What is Ptm?

A

Transmural pressure - difference between inside and outside of the vesse;

266
Q

What is Laplace’s law?

A

T = Ptm * r
Tension = transmural pressure * radius

267
Q

What parameter gives the best indication of perfusion to the foot?

A

Pressure

268
Q

What happens to pressure if velocity increases?

A

Pressure decreases

269
Q

What is pressure drop proportional to?

A

Mean velocity

270
Q

What is Darcy’s law?

A

Rf = 8Lu / Pi r^4

271
Q

Generally, what form of energy is highest in arteries?

A

Generally PE > KE
- but with very high velocity flow, inertial losses can overtake frictional losses

272
Q

What is Reynolds equation?

A

Re = 2 rp meanv / u
(is the ratio of inertial to viscous losses)

273
Q

What are the thresholds for Reynolds values?

A

< 2000 is laminar flow
2000 - 2500 is a disturbed intermediate flow
Re >2500 is turbulent

274
Q

What are the 4 assumptions based on the Bernoulli equation?

A
  1. fluid is incompressible
  2. fluid is ideal
  3. flow is incompressible
  4. flow is one dimensional
275
Q

What is the strength of focusing?

A

The ratio of the aperture width to the beam width at the focus

276
Q

What is the equation for focus strength?

A

a / W = a^2 / (F*lambda)
a = aperture width
W = focal width
F = focal length

277
Q

What is the focal zone?

A

Where beam width < 2 * the focal width

278
Q

What happens to focal width as aperture size increases?

A

Focal width decreases, with small spread in the far field

279
Q

What conditions are needed for strong focusing?

A

Wide aperture

280
Q

How does beam steering impact aperture size?

A

It reduces it - causes more spread

281
Q

Which hazard is in effect more at higher frequencies?

A

Heating
Heating is proportional to frequency

282
Q

Which hazard is more important at lower frequencies?

A

Acoustic cavitation
Acoustic cavitation is proportional to 1 / Sqrt(f)

283
Q

What are the units for TI and MI?

A

Decibels

284
Q

What is acoustic dose rate?

A

Rate of absorption of energy per unit mass

285
Q

What are the limits for TImax and MImax in the eye?

A

TI = 1
MI = 0.23

286
Q

What are the limits for TImax and MImax in the body?

A

TI = 6
MI = 1.9

287
Q

What are: TIS, TIB, TIC?

A

TIS = TI for soft tissue
TIB = TI for bone
TIC = TI for cranial bone

288
Q

What are the 3 main non-thermal hazards?

A
  1. Acoustic cavitation - oscillation of bubbles
  2. Gas-body effects - complete reflection at air-bubble interface
  3. Radiation pressure - streaming and shear stress
289
Q

How many MI values are there?

A

Just 1

290
Q

What causes cavitation?

A

Contrast agents

291
Q

Which 2D scanner controls do not affect TI and MI?

A

Gain, Dynamic range, TEQ/auto-optimize, MAPS

292
Q

Which 2D controls affect TI and MI?

A

Power
Freeze
Frequency
Compounding
Depth
Focus
X-res
Write zoom

293
Q

How can you reduce random errors?

A

Take repeat readings

294
Q

How do random errors change with number of repeats (n)?

A

Random error is proportional to Sqrt(n)

295
Q

How does a focused beam impact average velocity? and how can this impact be mitigated?

A

It can over-estimate average velocity (up to 30%)
- set range gate to straddle vessel and focus at range gate

296
Q

How many dimensions can an ultrasound beam be focused in?

A

3
- scan plane, elevation plane and steering plane

297
Q

Generally, what is the difference between the weakest and strongest echo?

A

10^5

298
Q

How does lower frequency impact MI and TI?

A

Lower frequency increases TI MI

299
Q

What is a hazard?

A

Anything that can cause harm

300
Q

How are energy and pressure related?

A

Energy is proportional to pressure squared

301
Q

What is viscous diffusion?

A

The process of the boundary layer spreading from the wall to the centre of the vessel

302
Q

What is inlet length?

A

Length after entrance that it takes for flow to become parabolic

303
Q

What is Laplace’s Law?

A

T = Ptm * r
S = Ptm *r / h

304
Q

How is K calculated?

A

K = -V change in P / change in V
- is minus because an increase in pressure causes a decrease in volume

305
Q

What is Moens-Korteweg Equation?

A

Pulse wave velocity equation

306
Q

What are equations for Z?

A

z = pc = Sqrt(pK) = 1/A Sqrt(pEh / 2r) = local P / local v

307
Q

What is PI?

A

(PSV - EDV) / Mean V

308
Q

What is RI?

A

(PSV - EDV) / PSV

309
Q

How is bandwidth measured?

A

Full width at half maximum

310
Q

What does a high and low Z mean?

A

High = large pressure, little response
Low = little pressure, large response

311
Q

What happens to Z and pulse wave velocity with age?

A

Z and PWV increase due to the increase in E (stiffness) of vessels (Moens-korteweg Eq)

312
Q

What is Snells Law?

A

Sin(theta2) / Sin(theta1) = c2 / c1

313
Q

What is the interference of waves with a 180 degree phase difference?

A

Cancellation

314
Q

What is the interference of waves with a 90 degree phase difference?

A

1.5x superposition

315
Q

What is the interference of waves with a 360 degree phase difference?

A

2x superposition

316
Q

What is the interference of waves with a 270 degree phase difference?

A

0.5x cancellation

317
Q

What is the equation for spread in the far field?

A

Sin(theta) = wavelength / a
- theta = half angle of spread, a = half aperture width

318
Q

What are Huygens wavelets?

A

Many individual point sources next to each other. Plane parallel waves at the centre but beam divergence at edge

319
Q

Which aspect of the beam can be focused?

A

Only the near field

320
Q

When would you not get grating lobes?

A

When the spacing between individual elements is < 1 wavelength

321
Q

What are the units for attenuation coefficient?

A

dB cm-1 MHz-1

322
Q

What is a point source?

A

Is much smaller than the wavelength of sound - beam diverges in all directions

323
Q

What is the equation for the NFL?

A

NFL = a^2 / wavelength
a = half aperture width

324
Q

What is the typical attenuation coefficient of soft tissue?

A

0.7db cm-1 MHz-1

325
Q

What is axial resolution dependent on?

A

Pulse length and therefore frequency, number of cycles and wavelength

326
Q

How does increasing frequency impact NFL?

A

It increases NFL

327
Q

What do zero-crossing detectors display?

A

(Sqrt(mean v))^2

328
Q

What is the duty factor?

A

Pulse duration / PRF

329
Q

What factor usually limits frame rate?

A

The speed of sound, c

330
Q

What is the range equation?

A

c = 2d / t

331
Q

What is the vmax without aliasing equation?

A

c^2 / 8d ft Cos(theta)

332
Q

What is the wave shape when all harmonics are added?

A

Pure square wave

333
Q

What are the 2 ways of utilising harmonics?

A
  1. High-pass filter - removes fundamental frequency
  2. Pulse inversion method - 2 pulses of opposite phase are transmitted in sequence - cancel out
334
Q

What are the disadvantages of using harmonics?

A

Weaker echoes so penetration is poor

335
Q

How does attenuation change with depth?

A

It increases exponentially

336
Q

What are the 2 causes of ISB?

A
  1. Finite pulse length = range of frequencies
  2. Different doppler angles, not known, edge vs mid
337
Q

What generates harmonics?

A

The non-linear propagation of ultrasound waves, whereby the peaks (compressions) travel faster than troughs (rarefactions) which distorts the waves and generates multiples of the fundamental frequency

338
Q

What is Darcy’s Law?

A

P = QR

339
Q

What is the Wormersley parameter?

A

The ratio of inertial to viscous forces for pulsatile flow (like Re but for pulsatile flow)

340
Q

What does a high Wormersley parameter indicate?

A

Inertial forces dominate

341
Q

What does a Wormersley parameter below 1 indicate?

A

Viscous forces dominate

342
Q

How is Young’s Modulus, E, calculated?

A

stress / strain

343
Q

How are mmHg and Pa related?

A

1 mmHg = 133.3 Pa

344
Q

How are pressure and velocity related?

A

Increase in velocity decreases pressure

345
Q

What is a Newtonian fluid?

A

One whose viscosity is not impacted by shear rate

346
Q

What 2 components contribute to boundary layer formation?

A
  1. Fluid viscosity
  2. no-slip condition next to vessel wall
347
Q

What is the equation for beam width at the focus?

A

W = F * wavelength / a
F = focal length
a = half aperture width

348
Q

What is the focal zone?

A

Focal zone is where beam width is < 2x the width at the focus

349
Q

What happens to wave amplitude when it is reflected at an interface of high to low impedance?

A

Amplitude is negative

350
Q

When does phase inversion occur at an interface?

A

When we go from high to low impedance (negative amplitude of reflection) then the phase is inverted. e.g. at probe-skin interface

351
Q

What does the movement of a target between pulses cause?

A

A phase difference between the two pulses

352
Q

How does density impact absorption coefficient?

A

Increased density e.g. bone causes increased absorption coefficient

353
Q

What is temporal peak intensity?

A

The highest intensity found within a pulse

354
Q

What is temporal average intensity?

A

The intensity averaged across the whole pulse cycle - including the dead time between pulses

355
Q

What is the pulse average intensity?

A

Intensity averaged across the whole pulse cycle, not including dead time

356
Q

What are the two main classes of hazard?

A

Thermal and non-thermal

357
Q

What are the two types of cavitation?

A

Stable cavitation - causes microstreaming
Collapse cavitation - causes physical damage and free radicals

358
Q

What are the two groups of non-thermal effects?

A

Non-cavitational and cavitational

359
Q

What is radiation force?

A

Energy absorbed by the tissue in the direction of ultrasound propagation

360
Q

What is cavitation?

A

The compression and stretching of molecular gas structures when ultrasound passes through them

361
Q

How can bubble collapse cause chemical damage during cavitation?

A

Bubble collapse causes extremely high localised pressure and temperature increases. This causes large mechanical stresses on the surrounding medium and potentially creates free radicals which can cause chemical damage

362
Q

What do thermal effects depend on?

A

The average energy input to the tissue

363
Q

What do non-thermal effects depend on?

A

The amplitude and length of the individual pulses
- particularly the negative pressure experienced during rarefaction

364
Q

What causes bubble collapse?

A

The transition from a large negative pressure to a positive pressure

365
Q

What are the simplest for of contrast agents for CEUS?

A

IV saline that has been shaken up

366
Q

How are harmonics generated during CEUS?

A

At high intensities, contrast agent mechanical oscillation becomes non-linear = easier for bubbles to expand than contract. They then radiate harmonics

367
Q

How does B-flow visualise flow?

A

It analyses the speckle pattern and compares at different times using code-excitation
- speckle pattern should remain the same when there is no movement = zero signal
- speed and turbulence = greater signal detection

368
Q

What is the maximum number of transmit focal zones possible for each pulse?

A

1
One pulse is needed per focal zone

369
Q

Name some different artefacts?

A

Post-cystic enhancement
Speckle
Acoustic shadowing
Refraction
Reflection
Comet-tail
slice thickness

370
Q

What are 6 assumptions of ultrasound?

A
  1. Speed of sound is constant in the body
  2. Attenuation is constant and uniform
  3. The beam axis is straight throughout the range of the beam
  4. Later echoes result from targets at greater depth
  5. The ultrasound beam is infinitely thin
  6. The image is acquired instantly
371
Q
A

Vascular 1 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions