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Term 1 > Physics > Flashcards

Physics Flashcards

1
Q

Anechoic

A

-without internal echoes

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2
Q

Echogenic

A
  • a region in an ultrasound image which has echoes

- synonymous terms: reflective, echo producing, echoic

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3
Q

Heterogenous

A

-variable levels of echogenicity

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4
Q

Homogeneous

A

-uniform echo texture

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5
Q

Hyperechoic

A

-displayed echoes that are relatively brighter than the surrounding tissue

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6
Q

Hypoechoic

A

-displayed echoes that are relatively darker than the surrounding tissue

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7
Q

Isoechoic

A

-having the same echogenicity (brightness) as the surrounding tissue

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8
Q

mega (M)

A

10^6

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9
Q

kilo (k)

A

10^3

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10
Q

deci (d)

A

10^-1

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11
Q

centi (c)

A

10^-2

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12
Q

milli (m)

A

10^-3

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13
Q

micro (u)

A

10^-6

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14
Q

What is sound?

A
  • a travelling variation in acoustic variables

- a longitudinal, compressional wave

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15
Q

What are acoustic variables?

What are some examples of acoustic variables?

A
  • quantities that vary in a sound wave

- examples: pressure, density, and particle motion

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16
Q

What is compression?

A
  • when molecules are pushed together, it produces a region of increased density; creating a zone of high pressure
  • compression describes the formation of a high pressure region
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17
Q

What is rarefaction?

A
  • when molecules release (or bounce back) there is a zone of decreased density
  • the rarefaction describes the creation of this low pressure
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18
Q

What is a longitudinal wave?

A

-a mechanical compressional wave in which back and forth particle motion is parallel to the direction of wave travel

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19
Q

What is frequency?

A

-a count of how many complete variations in pressure (cycles) go through in one second

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20
Q

What is the frequency range for audible sound?

A

20Hz - 20 000Hz

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21
Q

What is the frequency range for ultrasound?

A

> 20 000Hz

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22
Q

What is the period?

A
  • a function time

- the time it takes for a sound wave to complete 1 cycle

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23
Q

As frequency increases, what happens to the period and why?

A
  • T decreases
  • more cycles per second will equal shorter cycles
  • they are inversely proportional
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24
Q

What is wavelength?

A

-the length of space over which one cycle occurs

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25
Q

What is acoustic velocity (c)?

A

-the speed of a wave movement through a medium

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26
Q

If frequency increases, what will happen to wavelength and why?

A

-if frequency increases, wavelength decreases, because they are inversely related

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27
Q

What determines acoustic velocity?

A

-a medium’s stiffness

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28
Q

What is stiffness?

A

-a medium’s resistance to compression

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29
Q

Which materials have the highest acoustic velocity? (solids, liquids, gases)

A

solids > liquids > gases

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30
Q

What is the average acoustic velocity in soft tissue?

A

1.54 mm/us OR 1540 m/s

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31
Q

What materials are at the higher and lower ends of the scale for acoustic velocity?

A
  • bone is higher than soft tissue
  • lung is very low
  • soft tissue is in the middle and are all within a tight range
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32
Q

Describe pulse echo technique in the use of ultrasound.

A

The transducer sends out a pulse which reflects off a boundary and returns to the transducer. The echo(es) is/are then represented as a dot on the screen. It’s brightness depends on the strength of the returning echo.

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33
Q

Describe harmonics production.

A

The more dense/high pressure areas of the sound beam move faster than the less dense areas. This changes the waveform and produces multiples of the original fundamental frequency.

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34
Q

What are the first 3 odd harmonic frequencies of a sound wave with fundamental frequency=5MHz?

A

15MHz, 25mHz, 35MHz

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35
Q

What is CW?

A

-continuous wave transmission continuously emits a constant frequency with constant peak pressure amplitude sound waves from the force

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36
Q

What is pulsed ultrasound?

A
  • not a continuous wave

- a few cycles of ultrasound, separated by a gap of no sound

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37
Q

What is PRF and what is it’s unit?

A
  • the number of pulses occurring in a second

- kHz

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38
Q

What is PRP and what is it’s unit?

A
  • the time from the beginning of one pulse to the beginning of the next
  • ms
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39
Q

If PRF increases, what happens to PRP, and why?

A
  • PRP will decrease

- they are inversely proportional

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40
Q

What is PD?

A
  • the time for one pulse to occur

- from the beginning to the end of one pulse

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41
Q

What is the typical number of cycles in an ultrasound pulse?

A

2 or 3

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42
Q

What is the typical number of cycles in a doppler pulse?

A

5 to 30

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43
Q

If frequency increases, what will happen to PD and why?

A

-PD will decrease with an increase in frequency, because a higher frequency will generate a shorter period, which will decrease the PD

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44
Q

What is the advantage of a shorter PD?

A

-shorter PD = better image (resolution)

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45
Q

What is DF?

A

-the fraction of time that a pulsed ultrasound is on

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46
Q

If PD increases, what happens to DF and why?

A

-increasing PD will increase DF, because they are directly proportional

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47
Q

What is SPL, and what is it’s significance?

A
  • the length of space over which a pulse occurs
  • unit is mm
  • it is significant because it improves image resolution
  • shorter pulse lengths improve resolution
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48
Q

If frequency increases, what happens to SPL?

A
  • SPL will decrease with an increase in frequency
  • SPL is directly related to wavelength and wavelength is inversely related to frequency, therefore any change in frequency will affect SPL indirectly
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49
Q

What affects bandwidth?

A

SPL

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50
Q

Which is better: a larger/smaller bandwidth?

A

-larger is better

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51
Q

Which is better: a QF of 3 or 0.4?

A

0.4

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52
Q

What is intensity?

A

-the rate at which energy passes through a unit area

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53
Q

If power increased, what would happen to intensity?

A

-intensity would increase proportionately with power

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54
Q

If the area increased, what would happen to intensity?

A

-intensity would decrease proportionately with the area

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55
Q

How do you change the area of an ultrasound beam?

A

-focus the beam

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56
Q

What is the amplitude of a wave?

A
  • the maximum variation that occurs in an acoustic variable

- measured from the baseline to the peak

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57
Q

What is power?

A

-the rate at which work is performed or energy is transmitted

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58
Q

Attenuation

A

-weakening of sound

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59
Q

weaker signal =

A

weaker echoes

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60
Q

TGC

A
  • Time Gain Compensation

- provides amplification of specific field echoes

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61
Q

What is attenuation is soft tissue?

A

0.5dB/cm MHz

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62
Q

Half Value Layer

A
  • thickness of material that will half the original intensity
  • distance it takes to drop 3dB
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63
Q

What is the opposite of reflection?

A

transmission

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64
Q

IRC + ITC =

A

1 or 100%

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65
Q

What is impedance directly proportional to?

A

density and propagation speed

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66
Q

What are specular reflectors?

A
  • diaphragm
  • fascia
  • bone
  • sound bounces back and produces a strong echo
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67
Q

When does scattering occur?

A

-when the boundary is not smooth

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68
Q

Scattering

A

-redirection of sound in many directions

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69
Q

What does scattering depend on?

A

-operational frequency and scatter size

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70
Q

Which is more likely to scatter? (a Lg or Sm wavelength)

A

-a large wavelength is more likely to scatter

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71
Q

Backscatter

A

-echo info that comes back to transducer

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72
Q

What does a large reflection mean?

A

-large difference between impedances (z)

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73
Q

What happens when there is a small difference between impedances (z)?

A

-most will transmit

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74
Q

What do contrast agents produce?

A

-harmonic frequencies

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75
Q

What is round trip travel time in soft tissue?

A

13us/cm

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76
Q

Is sound a mechanical wave?

A

Yes.

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77
Q

Is sound ionizing radiation?

A

No.

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78
Q

Is sound electromagnetic?

A

No. Electromagnetic waves do not require a medium.

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79
Q

Can sound converge/diverge?

A

Yes.

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80
Q

What are other words for a transducer?

A
  • probe
  • scan head
  • transducer assembly
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81
Q

Transduce

A
  • convert one form of energy into another
  • voltage to sound
  • sound to voltage
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82
Q

Piezoelectricity

A

piezo (press) + electron (amber)

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83
Q

Piezoelectric Effect

A

-sound to voltage

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84
Q

Converse/Reverse Piezoelectric Effect

A

-voltage to sound

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85
Q

Piezoelectric Element (aka crystal)

A
  • adding a voltage causes thickness of the element to change
  • creates a mechanical wave
  • returning echo affects the element (creates a voltage)
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86
Q

1 cycle of alternating voltage =

A

2/3 cycles of pulse

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87
Q

longer AV =

A

longer pulse (doppler)

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88
Q

Quartz

A

-one of the first natural piezoelectric crystals

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89
Q

What piezoelectric elements do we use now?

A

-synthetic crystals (often ceramics)

1 Substance:

  • lead
  • zirconate
  • titanate
  • called PZT

-barium

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90
Q

What are piezoelectric elements usually made of?

A
  • PZT

- aka lead zirconate titanate

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91
Q

How do we realign molecular dipoles?

A

-place a strong magnetic field at a high temp. (350 degrees)

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92
Q

Polarization

A

-aligned dipoles

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93
Q

What do piezoelectric elements do while in magnetic field?

A

-cooled

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94
Q

Curie Point

A

-the temp. in which the magnetic properties of a sound can be changed

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95
Q

What is the curie point go PZT?

A

350 degrees

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96
Q

What would happen if thou brought the crystal back to the Curie Point, but without the magnetic field?

A
  • dipoles will scatter

- not piezoelectric anymore

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97
Q

What frequency does piezoelectric element (aka crystal) have?

A
  • natural vibrational frequency
  • fundamental frequency
  • operational frequency
  • resonance frequency

*they are all the same, just different names

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98
Q

What does operating frequency depend on?

A

-the element

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99
Q

Wavelength of US =

A

2x thickness of material (2 x th)

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100
Q

Multi Hertz Operation

A

-2 or 3 frequencies on the same element

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101
Q

How can operation frequency be adjusted?

A

-change voltage

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102
Q

Does PRF of voltage affect PRF of pulse?

A

Yes.

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103
Q

PRF volt =

A

PRF pulse

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104
Q

If you go further away, what do you have to decrease?

A

PRF

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105
Q

If you don’t decrease PRF when you go further, what happens?

A
  • range ambiguity (artifact)
  • echo misplacement (artifact)

-happens from sending pulses too fast (before the other now is back)

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106
Q

pen

A
  • penetration

- aka depth

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107
Q

Damping Material

A
  • aka backing material
  • metal powder (tungsten) and plastic/epoxy resin
  • on the back of the element
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108
Q

What is the damping materials impedance similar to?

A

crystal

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109
Q

What does a damping material reduce?

A
  • ringing (ex. bell wrapped in rubber)
  • cycles per pulse (n)
  • amplitude (this is bad, weaker echo)
  • sensitivity (this is bad, ability to detect weaker echoes)
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110
Q

What do a lower PD and a lower SPL result in?

A

better resolution

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111
Q

Does CW have damping material?

What does this result in?

A

No.

  • better sensitivity
  • worse penetration
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112
Q

House Unit/Case

A
  • usually same material as damping
  • prevents moisture
  • protects internal structures
  • absorbs energy from sides of crystal
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113
Q

What is the purpose of matching layer?

A

-to reduce the difference in z

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114
Q

Footprint

A

-width of probe head

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115
Q

Do higher frequency transducers have smaller or larger footprints?

A

-smaller

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116
Q

What does a smaller beam width mean?

A
  • stronger intensity (picks up more signals)

- better resolution

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117
Q

What does focusing do?

A

-improves resolution (only in the NZL)

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118
Q

Where is beam width decreased?

A

-focal region

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119
Q

Focal Length

A

-distance from transducer to the focal region

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120
Q

Natural Focus

A

-beam will naturally come to focus

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121
Q

What are other names for the near zone?

A
  • fresnel zone

- near field

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122
Q

NZL

A

-region from transducer to min beam width

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123
Q

Beam Convergence

A

-beam width decreases with increasing distance from the transducer

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124
Q

What are other names for the far zone?

A
  • fraunhofer zone

- far field

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125
Q

Far Zone

A

-region beyond the NZL

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126
Q

Beam Divergence

A

-beam width increases with increasing distance from transducer

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127
Q

Aperture

A
  • opening

- width of element(s)

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128
Q

Beam Profile

A

-width (wb)

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129
Q

What does beam width change with?

What does it affect?

A
  • depth

- affects resolution and intensity

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130
Q

Is intensity uniform within a beam?

A

No

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131
Q

Is power uniform within a beam?

A

Yes

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132
Q

What is the width at the focus?

A

0.5 aperture size

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133
Q

What is NZL determined by?

A
  • size of element (aperture)

- operating frequency

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134
Q

Focal Length

A
  • aka NZL

- distance to focus

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135
Q

Why is transducer care important?

A
  • prevention of nosocomial infections

- there is no infectious disease screening before exams

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136
Q

Critical

A
  • device enters otherwise sterile tissue
  • ex. intraoperative applications

Level of Disinfection: sterilization

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137
Q

Semi-Critical

A
  • device contacts mucous membranes
  • ex. endocavity applications

Level of Disinfection: high

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138
Q

Non-Critical

A

-device contacts intact skin

Level of Disinfection: intermediate or low

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139
Q

Transducer Care

A
  • store in clean holders/racks
  • keep cord off floor
  • wipe probe and cord between patients
  • use carrying case for transport
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140
Q

Low Level Disinfection

A
  • use of sterilization wipes/solutions
  • no bleach, ammonia or alcohol bases
  • no sprays
  • 5% hydrogen peroxide
  • cavi wipes
  • preempt (wipes)
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141
Q

High Level Disinfection

A
  • invasive transducers are soaked
  • cidex
  • recert
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142
Q

Invasive Transducers

A
  • transvaginal
  • transrectal
  • transesophageal
  • catheter mounted
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143
Q

What are the benefits of invasive transducers?

A
  • get us much closer to the tissue (higher resolution)

- can use high frequency without worrying about attenuation

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144
Q

What is a drawback for invasive transducers?

A

-high risk of infection without proper sterile techniques

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145
Q

What does resolution allow for?

A
  • the ability to image fine detail
  • ‘better’ picture
  • being able to separate distinct echoes
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146
Q

Why is a smaller resolution better?

A

-smaller details can be discerned

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147
Q

What happens if 2 reflectors are not separated sufficiently?

A

-they produce overlapping echoes

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148
Q

Axial Resolution

A

-minimum reflector separation along scan line to produce separate echoes

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149
Q

What are other names for axial resolution?

A
  • longitudinal
  • radial
  • depth
  • range
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150
Q

If the axial resolution is 2mm, structures 2mm apart will be seen as ___ structure(s).

A

2

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151
Q

If the axial resolution is 2mm, structures 1mm apart will be seen as ___ structure(s).

A

1

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152
Q

Do we want a smaller or larger AR?

A

-smaller is better

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153
Q

AR

A

Axial Resolution

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154
Q

How do we improve AR?

A

-reduce SPL

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155
Q

How do we reduce SPL?

A
  • reduce ‘n’ by reducing damping layer

- reduce wavelength by increasing operating f (will affect penetration)

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156
Q

What are some other names for lateral resolution?

A
  • angular
  • transverse
  • azimuthal
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157
Q

Lateral Resolution

A

-minimum reflector separation perpendicular to scan LINE to produce separate echoes

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158
Q

LR

A

-lateral resolution

159
Q

Do we want a sm or lg LR?

A

-smaller is better

160
Q

How is LR improved?

A

-reducing beam width (by focusing)

161
Q

Elevational Resolution

A
  • minimum reflector separation perpendicular to scan PLANE to produce separate echoes
  • 3rd dimension
162
Q

A beam has slice thickness, which can also be known as __________ or __________.

A
  • section thickness

- elevational plane

163
Q

What can elevational resolution produce?

A

-section thickness artifact (aka partial volume artifact)

164
Q

What does elevational thickness do?

A

-filling in of cysts or other anechoic structures (ex. GB, vessels, urinary bladder)

165
Q

What will a poor evolutional resolution show?

A

-echoes from outside the intended scan plane (especially with anechoic structures)

166
Q

How do we fix elevational resolution artifact?

A

THI

  • narrower and thinner beam
  • less likely to pick up echoes from other plane

Spatial Compounding

167
Q

Temporal Resolution

A

-being able to separate echoes in real time

168
Q

What does poor temporal resolution visualize as?

A

-lag

169
Q

Contrast Resolution

A

-being able to separate 2 different shades of grey

170
Q

Useful Frequency Range

A

2 to 10 MHz

171
Q

What do higher frequencies increase?

A

-resolution

172
Q

What do higher frequencies decrease?

A

-max imaging depth

173
Q

When may a frequency up to 50MHz be used?

A
  • opthalmologic imaging
  • dermatologic imaging
  • intravascular imaging
174
Q

What does electronic focus eliminate the need for?

A
  • a lens

- curved elements

175
Q

How can focus be achieved in the third dimension (perpendicular scanning plane)?

A
  • a lens

- curved element

176
Q

How can phasing be applied to focus in the third dimension electronically?

A

-with at least 3 rows of elements

177
Q

What do 2D rays have the ability to do?

A

-steer and focus in 2 dimensions

178
Q

1D array is…

A

-2D imaging

179
Q

2D array is…

A

-3D imaging

180
Q

4D imaging =

A

3D imaging + time

181
Q

What is 3D imaging mostly used for?

A
  • obstetrics

- breast

182
Q

What is 3D imaging also known as?

A
  • volume imaging

- volumetric scanning

183
Q

Reception Steering

A

-listening from a particular direction

184
Q

Dynamic Focusing

A

-continual change of the focus with increasing depth

185
Q

Dynamic Aperture

A

-as the focus continues to change during echo reception, the aperture will increase to maintain a constant focal width

186
Q

Annular Arrays

A
  • concentric rings

- piezoelectric material carved out in rings

187
Q

Why aren’t annular arrays used anymore?

A

-we can do the same thing with phasing and electronic phasing

188
Q

Hemodynamics

A

-study of blood flow

189
Q

What is the motion of heart and blood flow detected with?

A
  • doppler effect

- detects, quantify’s and evaluate’s blood flow

190
Q

Circulatory System

A
  • heart
  • arteries
  • arterioles
  • capillaries
  • venules
  • veins
191
Q

How many L of blood do humans have?

A

5L

192
Q

What does blood consist of?

A
  • plasma
  • RBC
  • WBC
  • platelets
193
Q

Blood Functions

A
  • heat regulation
  • oxygen
  • carbon dioxide
  • nutrients to cells
  • removal of waste from cells
194
Q

Heart

A
  • 4 chambers: 2 atria, 2 ventricles
  • cardiac muscles
  • valves
195
Q

Which arteries are oxygen poor?

A

-pulmonary arteries

196
Q

Which veins are oxygen rich?

A

-pulmonary veins

197
Q

Valves

A
  • one way
  • prevent back flow of blood
  • in heart and veins
198
Q

Stenotic Valves

A

-don’t open enough (pathology)

199
Q

Insufficiency/Regurgitation (valves)

A

-don’t close enough (pathology)

200
Q

Hydrostatic Pressure

A
  • equivalent to the weight of a column of blood

- increases with distance below the heart

201
Q

What is the hydrostatic pressure in a supine patient?

A

0 mmHg

202
Q

What is the hydrostatic pressure in a standing patient?

A

100 mmHg

-pressure in veins is much higher

203
Q

Respiration is also known as…

A

-phasicity

204
Q

Inspiration

A
  • diaphragm moves down
  • increase in thorax volume, decrease in thoracic pressure
  • allows air into lungs
  • decrease in abdominal volume, increase in abdominal pressure
  • stops venous return from the legs
205
Q

Valsalva

A
  • patient can be asked to hold their breath and ‘bear down’
  • increase in abdominal pressure
  • stops venous return from legs
206
Q

Expiration

A
  • diaphragm moves up
  • decrease in thoracic volume, increase in thoracic pressure
  • increase in abdominal volume, decease in abdominal pressure
  • venous blood returns from legs
207
Q

Pressure

A

-driving force behind fluid flow

208
Q

What is required for fluid flow?

A

-pressure difference/gradient

209
Q

Which way does fluid flow?

A

-area of high pressure to area of low pressure

210
Q

Volumetric Flow Rate

A
  • volume of blood passing a point per unit of time

- LONG STRAIGHT TUBE (we assume vessels in the body are long straight tubes)

211
Q

R

A

resistance

212
Q

Viscocity

A

-resistance to flow offered by fluid

213
Q

What has the strangest effect on resistance?

A

-radius or diameter

214
Q

What does resistance depend on?

A

-radius to the 4th power

215
Q

If the radius doubles, what happens to R?

A

-decreases 16x

216
Q

Vasoconstriction

A
  • smaller blood vessels

- restricts blood flow

217
Q

Vasodilation

A
  • larger blood vessels

- allows more blood flow (when needed)

218
Q

Types of Flow

A
  • laminar

- turbulent (non laminar)

219
Q

Types of Laminar Flow

A
  • plug flow
  • parabolic
  • disturbed flow
220
Q

Plug Flow

A
  • at the entrance to tubes
  • blood moves as a unit
  • same speed across the vessel
221
Q

Parabolic/Laminar

A
  • after entering the straight tube

- fastest speeds in the centre of tube

222
Q

Where do we assess in doppler?

A

-centre of the vessel (where it is fastest)

223
Q

Where is the slowest speed?

A
  • tube wall

- at 0

224
Q

Average flow speed =

A

1/2 of fastest speed

225
Q

Disturbed Flow

A
  • at stenosis
  • at bifurcation
  • still laminar, but streamlines are not straight
  • non parabolic
226
Q

Turbulent Flow

A
  • usually after a significant stenosis
  • chaotic, multidirectional, multispeed flow
  • non laminar
  • eddies
  • overal forward flow
227
Q

What time of flow may physicians heart bruit with?

A

-turbulent flow

228
Q

What does turbulent flow depend on?

A

-Reynolds #

229
Q

What is critical Reynolds number?

A

2000 for blood

-flow must surpass a critical Reynolds # to cause turbulent flow

230
Q

Stenosis

A

-partial blockage

231
Q

Occlusion

A

-complete blockage

232
Q

As heart beats…

A

-pressure and speed go up and down

233
Q

what do we observe in compliant vessels?

A

1) added forward flow

2) reversal of flow

234
Q

Compliance

A

-expansion and contraction of non ridging vessels during systole and diastole

235
Q

Windkessel Effect

A

-aka added forward flow

236
Q

Systole

A

-vessel expands

237
Q

Diastole

A
  • vessel contracts

- results in extended flow w/o driving pressure from heart

238
Q

Flow Reversal

A

During Diastole

  • in AO, blood doesn’t flow back because the aortic valve closes
  • sometimes in distal circulation, when pressure decreases and vessel contracts, there will be reversal of flow (no valves to prevent back flow)
239
Q

Continuity Rule

A

-speed goes up at a stenosis to keep volumetric flow rate (Q) constant at all 3 regions (before, at and after stenosis)

240
Q

What happens to speed and pressure at a stenosis?

A
  • speed goes up

- pressure goes down

241
Q

What does the continuity rule apply to?

A
  • volumetric flow rate for a short segment (constant)

- usually taking about a stenosis

242
Q

Q = V x A

What happens when A decreases?

A

-V increases to keep the same amount of blood going through (continuity rule)

243
Q

What is the point of the continuity rule?

A
  • if we can figure out how fast the blood is going at a stenosis, we can figure out how much it is stenosed
  • V will determine the severity
244
Q

Bruit

A

-sound produced by a stenosis

245
Q

Bernoulli Effect

A

-decrease in pressure in regions of high flow speed (at stenosis)

246
Q

Before Stenosis:

Bernoulli Effect

A

-pressure goes up to push blood through stenosis

247
Q

At Stenosis:

Bernoulli Effect

A
  • pressure goes down to maintain energy

- pressure energy to flow energy

248
Q

After Stenosis:

Bernoulli Effect

A

-flow energy to pressure energy

249
Q

Ultrasound Basics

A
  • sound wave is sent out at a particular frequency
  • bounces off stationary structure
  • returns at the same frequency that it was sent out
250
Q

Doppler Effect

A

-change in frequency caused by the motion of a source, reflector or receiver

251
Q

How do we know if the frequency will come back higher or lower?

A

-if the object is moving closer or further away

252
Q

Doppler Shift

A

-difference between the sent a returning frequencies of a sound wave

253
Q

What happens to the frequency if we are getting closer together?

A

-increases (positive shift)

254
Q

What happens to the frequency if we are getting further apart?

A

-decreases (negative shift)

255
Q

What shift does blood coming towards the transducer have?

A

-positive

256
Q

what shift does blood moving away from the transducer have?

A

-negative

257
Q

In Doppler…

A
  • we fire a particular frequency
  • measure the frequency that returns
  • calculate how fast the object is moving
258
Q

How do we affect the doppler shift?

A

-changing frequency

259
Q

What can doppler shift calculate?

A

-velocity

260
Q

Are we directly affecting the velocity by changing the frequency?

A

No.

261
Q

Doppler effect Applications

A
  • police speed detectors
  • weather forecasting
  • door openers
  • burglar alarms
262
Q

When does lesser doppler shift occur?

A

-if the angle of interrogation is non zero

263
Q

What do we incorporate to compensate for lesser shift?

A

cos

264
Q

Doppler Angle

A

-angle between the sound beam and the vessel

265
Q

What does doppler shift depend on?

A

-cosine of doppler angle

266
Q

cos 0 =

A

1

-hitting vessel straight on

267
Q

cos 30 =

A

0.87

268
Q

cos 60 =

A

0.5

269
Q

cos 90 =

A

0

-hitting vessel perpendicular

270
Q

What affects out calculated doppler shift?

A

-doppler angle

271
Q

When is doppler shift less?

A

-when incorporating non zero angles

272
Q

What does a decease in doppler shift measurement mean?

A

-decrease in velocity measurement

273
Q

What happens if we don’t incorporate cos?

A

-velocity measurements are off

274
Q

What degree do we want to hit vessels at?

A

0

-nearly impossible

275
Q

What are some techniques to get close to a 0 doppler angle?

A

1) heel toe
2) phase (steer)
3) angle correct

276
Q

Doppler Angle Correct

A
  • we can tell the machine that we are off and it compensates

- increased our velocity back to where it should be

277
Q

When will there be an increased error in speed calculation?

A

-with a higher angle

278
Q

What angle do we work under?

A

60

279
Q

Doppler Blood Flow

A
  • presence (yes/no)
  • speed (slow/fast)
  • character (laminar/turbulent)
  • direction
280
Q

Doppler Displays

A
  • colour
  • spectral
  • audible
281
Q

Colour Doppler

A
  • aka colour flow imaging
  • presence, speed, character and direction of blood flow
  • assess a very large area at a time (vs. spectral doppler)
  • colour superimposed on grey scale image
282
Q

How do we steer colour doppler?

A
  • phasing
  • to get closer to 0 degrees
  • to avoid if vessels are parallel to surface
283
Q

How do we know if doppler shift has occurred?

A

-if the retiring echoes have a different frequency from the emitted

284
Q

How do we know if flow is moving toward or away from transducer?

A
  • depending on the sign of the doppler shift

- colour is assigned to pixels

285
Q

What is the difference in scan lines from colour and B mode?

A

Colour- multiple pulses are sent per scan line

B Mode- 1 pulse per scan line

286
Q

what is doppler shift calculated within?

A

-signal processor

287
Q

What does the signal processor detect?

A

Signal Processor Parameters:

  • direction
  • mean
  • variance
  • power
288
Q

What is direction based on? (colour doppler)

A

+/- doppler shift

289
Q

Mean/Average Velocity (colour doppler)

A

-average velocity of blood in an area is calculated and displayed

290
Q

Variance (colour doppler)

A
  • the variety within the blood flow

- soft tissue deviation

291
Q

Power/Strength of Echo (colour doppler)

A
  • related to amplitude

- depends on reflectors, impedance and concentration of RBC’s

292
Q

Reflectors

A

-specular reflection vs scattering

293
Q

Impedance

A

higher impedance mismatch = more reflection

294
Q

Concentration of RBC’s

A

higher concentration = more reflection

295
Q

Math Technique for Colour Doppler (autocorrelation)

A
  • done with signal processor

- determines mean and variance

296
Q

How many pulses per scan line are sent out for colour doppler?

A
  • 3 to 32 per scan line

- usually 10 to 20

297
Q

Ensemble Length

A

-# of pulses/scan line

298
Q

More pulses for…

A
  • accuracy of speed calculation

- sensitivity (picking out weaker echoes/shifts)

299
Q

Where does the data go once the instrument process it?

A

-to the display

300
Q

What does the display use?

A
  • hue
  • saturation
  • luminance
301
Q

Hue

A

-what colour is shown

302
Q

Saturation

A

-amount of colour

303
Q

Luminance

A
  • brightness
  • echo intensity/power
  • similar to 2D echo intensity
  • stronger echoes will be brighter
304
Q

What can a monographer do to affect the effectiveness of the colour doppler examination?

A

Change the size of the colour box/window.

  • changes coverage
  • affects frame rate/temporal resolution
305
Q

What does colour map help to determine?

A

-mean velocities
-direction of flow
variance (change in colour from LT to RT)

306
Q

What colour spectrum is most commonly used?

A

-red/blue

307
Q

What shift does red usually indicate?

A

-positive

308
Q

What shift does blue usually indicate?

A

-negative

309
Q

Where is the + and - on the colour map?

A

+ on top

- on bottom

310
Q

Invert

A
  • slips the colour map

- does NOT change direction of flow

311
Q

Baseline

A
  • zero point (no doppler shift)

- can move the baseline up or down based on what you want to fit on your map

312
Q

Can you control PRF in doppler?

A

Yes.

313
Q

Can you control PRF in 2D?

A

No.

314
Q

What does changing the PRF in doppler do?

A
  • changed the scale (cm/s)

- increases or decreases speeds

315
Q

decrease in PRF is a ______ in scale.

A

-decrease

316
Q

An increase in PRF is a ______ in scale.

A

-increase

317
Q

What happens if the PRF scale is set too high?

A

-slower flows go undetected?

318
Q

What happens if your PRF scale is too high?

A

-faster flows alias

319
Q

Aliasing

A

-shows wrap around colour

320
Q

What does aliasing depend on?

A

Nyquist Limit

321
Q

Nyquist Limit =

A

1/2 PRF

322
Q

Are higher or lower velocities more likely to alias?

A

higher

323
Q

When will aliasing often show?

A

within a stenosis if PRF is set too low

324
Q

When can aliasing be good?

A
  • can adjust your PRF for the normal flow

- area of stenosis will show aliasing (highlights areas of highest velocity)

325
Q

Colour Gain

A
  • we can apply returning echo voltages (just like 2D)

- we want wall to wall filling

326
Q

Priority (colour control)

A

-aka echo write priority

Grayscale vs Colour Threshold

  • echoes below cut off amplitude will show as colour
  • stronger echoes show as grey scale
327
Q

Wall Filter

A
  • filters out noise (non useful info)
  • keeps the useful signal
  • eliminates any movement in the tissue that will produce doppler shifts
  • sets a cut off point
328
Q

Movement in Tissues that Produces Doppler Shifts

A
  • tissue vibration, vessel movement
  • aka clutter
  • have lower velocities
329
Q

Are arterial or venous speeds higher?

A

-arterial

330
Q

How can you fix aliasing?

A

-increase PRF (not too much)

331
Q

What happens if you increase PRF too much?

A

-echo misplacement

332
Q

What may a tortuous vessel look like in colour doppler?

A
  • flow reversal

- aliasing

333
Q

If you hit a vessel close o 90 degrees, what all it look like?

A

-no flow (occlusion)

334
Q

What does an increase in doppler angle reduce?

A
  • doppler shift

- corresponding flow

335
Q

Power Doppler

A
  • strength/intensity of echo
  • related to amplitude
  • determines by concentration of moving RBC’s
336
Q

Can we display just the power?

A

Yes.
0shows only presence of flow
-no velocity, direction, flow character

337
Q

Pro’s of Power Doppler

A

1) increased sensitivity
- slow flow
- small or deep vessels
2) angle dependant
3) no aliasing

338
Q

Con’s of Power Doppler

A
  • no speed/cannot quantify
  • no direction
  • no flow character to assess stenosis
339
Q

Duplex Scanning

A
  • doppler and gray scale
  • we update between the 2 (transducer does 1 at a time)
  • simultaneous (rapidly switches between the 2)
340
Q

Spectral Doppler

A

-firing alone a single scan line

341
Q

What is spectral doppler also called?

A
  • pulsed doppler

- pulsed wave doppler

342
Q

How many cycles/pulse does spectral doppler have?

A

5 to 30 cycles/pulse

343
Q

Spectral Doppler Parameters

A

-presence, speed, character and direction of blood flow

344
Q

Sample Volume

A
  • specific area that is being assessed

- aka gate

345
Q

Range Gating

A

-being able to select info from a specific depth

346
Q

Effective Sample Length =

A

1/2 SPL + gate length

347
Q

Sample Width =

A

beam width

348
Q

Is sample volume (SV) user defined?

A

yes

349
Q

Larger Gate Lengths

A

-looking for a vessel/signal

350
Q

Smaller Gate Lengths

A
  • more specific info
  • less noise
  • better quality of spectral waveform
351
Q

With spectral doppler, samples are taken and then ______.

A

smoothes

352
Q

Spectral Doppler
x axis =
y axis =

A

x axis = time

y axis = soppler shift/velocity

353
Q

Quadrature Phase Detector

A
  • allows detection of bidirectional doppler

- we can see +/- shifts

354
Q

Spectral Analyzer

A

-determines each doppler shift frequency and it’s strength

355
Q

Fast Fourier Transform

A
  • occurs within the spectrum analyzer
  • math technique to figure out the frequency spectrum
  • results sent to be displayed on the spectral display
356
Q

What does spectral display show?

A

-spectral waveforms

357
Q

Each point of spectral display shows…

A
  • direction (+/-)
  • magnitude (how fast)
  • amplitude (brightness)
358
Q

What affects direction of spectral waveform?

A
  • whether its coming towards or away from the transducer

- affected by direction of probe/steering

359
Q

What affects magnitude (cm/s) of spectral display?

A
  • speed of the blood flow

- doppler angle

360
Q

Doppler Angle

A
  • between the scan line and the blood flow

- can affect the calculated doppler velocity

361
Q

larger doppler angle =

A

smaller doppler shift

slower velocity calculated (w/o angle correct)

362
Q

What affects amplitude of spectral doppler?

A
  • brightness/intensity of returning echoes

- concentration of RBC’s/reflectors/impedances

363
Q

Spectral Doppler Controls

A
  • gate size/sample volume
  • gain
  • spectral invert
  • baseline

-very similar to colour doppler controls

364
Q

Gate Size/Smaple Volume (spectral controls)

A

-affects rangle resolution

365
Q

Range Resolution

A
  • knowing exactly where the signal is coming from

- opposite of range ambiguity

366
Q

Gain (spectral controls)

A

-amplification of incoming echo voltages

367
Q

Invert (spectral controls)

A
  • arteries are generally positive signals (above baseline)

- veins are generally negative signals (below baseline)

368
Q

Baseline (special doppler)

A
  • xero point

- ex. more + signals can move baseline down

369
Q

Wall Filter (spectral controls)

A
  • cuts off slower flows

- used to get rid of clutter (tissue motion, valves)

370
Q

PRF (spectral controls)

A

-PRF affects scale (which velocities we can display)

371
Q

What will happen to any doppler shift over Nyquist Limit?

A

-alias

372
Q

What happens if we decrease the PRF too much?

A

-aliasing (wrap around)

373
Q

What happens if we increase the PRF too much?

A

-poor signal (wasted space)

374
Q

Angle Correct (spectral control)

A
  • increased angle, decreased doppler shift

- makes it seem lower than it is

375
Q

What happens when you correct the angle?

A

-brings the calculated speed back to it’s true value

376
Q

Higher frequencies will have a ______ pitch.

A

higher

377
Q

What else can spectral doppler be converted to?

A

-audible sound

378
Q

Volume (spectral Controls)

A
  • audible signal can be turned up or down

- we can listen for areas of high speeds (higher pitch)

379
Q

Analyzing the Waveform

A

analyze spectral display with colour and grayscale info to assess for normal blood flow and pathology

380
Q

Arterial Signals

A
  • pulsatile

- higher velocity waveforms

381
Q

Venous Signals

A
  • phasic

- lower velocity waveforms

382
Q

Analyzing the Resistance of Flow in a Waveform

A

-assess the systolic portion and the diastolic portion

383
Q

High Resistance

A
  • ECA, extremities
  • quick upstroke
  • low diastole
384
Q

Low Resistance

A
  • ICA/CCA, blood hungry organs (liver, renal, etc.)
  • vasoldilation, slow upstroke
  • higher diastole
385
Q

Assessing Area of Stenosis

A
  • remember continuity rule
  • decrease in area, increase in velocity
  • surpassing Reynolds # = turbulence
386
Q

Spectral Broadening

A

wider range of spectra = more variety of shifts

  • narrowing the window
  • most obvious reason is stenosis
387
Q

Spectral Limitations

A
  • sonographers skill
  • movement
  • range gated to a specific depth
  • aliasing
388
Q

Fixing Aliasing

A
  • adjust baseline
  • lower operating f
  • increase doppler angle (lowers all doppler shifts)
  • increase PRF (increases Nyquist limit), allows for higher doppler shifts/velocities
389
Q

Spectral Limitations

A

-body habits (depth) limits PRF

390
Q

CW Doppler

A
  • occasionally used
  • 2 transducer elements (1 to send, 1 to receive)
  • oscillator (CW beam former) produced a voltage
  • sample volume = lg overlapping area
391
Q

Can continuous wave doppler alias?

A

No.
-aliasing happens because the shift is more than Nyquist limit
Nyquist limit = 1/2 PRF
-no PRF in CW

-can pick up high maximum values without aliasing

392
Q

CW Doppler Limitations

A
  • large sample volume
  • cant tell where its coming from
  • poor range resolution
393
Q

Does PW doppler have good range resolution?

A

excellent

Term 1 (17 decks)

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