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PHYS 314 > Bioeffects, Safety And Power > Flashcards

Bioeffects, Safety And Power Flashcards

1
Q

What is acoustic propagation?

A

The effect tissue has on sound

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2
Q

What factor is important to note about all ultrasound-induced adverse bioeffects?

A

They have occurred at higher intensities than diagnostic US.

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3
Q

When can potential biological effects occur?

A

When US propagates through human tissue

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4
Q

How can the strength of a wave be described and what are the three ways?

A

(The loudness/Volume)

  • Amplitude
  • Power
  • Intensity
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5
Q

How are power and intensity related?

A

Directly/Proportional

If power increases so does intensity

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6
Q

What is the formula for intensity?

A

Intensity = Power/Area

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7
Q

What is amplitude?

A

The particle displacement, particle velocity or acoustic pressure of a sound wave.

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8
Q

What is the maximum displacement of an acoustic variable?

A

Amplitude

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9
Q

How is amplitude demonstrated?

A

By a pressure wave that indicates the strength of the detected echo or the voltage induced in a crystal

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10
Q

What determines the initial amplitude of a pulse?

A

The pulser sends an amplitude of voltage to make the crystal ring.

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11
Q

As the pulse travels through the medium, what is the reduction in amplitude called?

A

Attenuation

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12
Q

What are the 5 mechanisms of attenuation?

A
  1. Absorption
  2. Reflection
  3. Refraction
  4. Scatter
  5. Wave front divergence
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13
Q

Does the amplitude of the echo decrease as the echo returns to the transducer?

A

Yes

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14
Q

How does intensity change?

A

In time and space

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15
Q

What is absorption?

A

80% of sound is attenuated by being converted to heat

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16
Q

Study ‘Particle Motion’ and ‘Attenuation’ cards

A

….

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17
Q

What is power?

A

A measure of the total energy transmitted summed over the cross sectional area of the beam per unit time

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18
Q

What is the formula for power?

A

Power = Intensity x Area

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19
Q

What is the absolute unit of power?

A

The watt (joules per second)

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20
Q

What is the relative unit of power?

A

Decibels (dB)

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21
Q

Look over the I, P, V (10log, 10log, 20l0g) stuff….

A

…

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22
Q

What determines the power?

A

The pulser does because power is an expression of strength

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23
Q

What does power default to?

A

100% or 0 dB and is relative to the exam being performed

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24
Q

In order from highest to lowest, what scanners have the highest output power? (SPTA)

A
  1. Pulsed Wave
  2. Colour Doppler
  3. B-Scan
  4. M-mode
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25
Q

Is the beam swept in PW?

A

No it is not swept unlike B Scan

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26
Q

What is intensity?

A

The measure of the strength of a sound wave

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27
Q

What is intensity equal to?

A

The power per unit area

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28
Q

What is the formula for intensity?

A

Intensity = Power/Area

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29
Q

What is the absolute unit of intensity?

A

mW/cm squared

OR

W/cm squared

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30
Q

What is the relative unit of intensity?

A

The decibel (dB)

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31
Q

What is the relationship between area and intensity?

A

Inversely proportional

If area decreases then intensity increases

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32
Q

Besides power, what else is intensity proportional to?

A

Intensity is proportional to the square of the pressure amplitude

I = amp^2

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33
Q

How does doubling the amplitude effect intensity?

A

Quadruples it

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34
Q

What determines the intensity coming out of the probe?

A

The amplitude of voltage

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35
Q

What happens to the intensity if the area is halved?

A

If the area is halved, the intensity doubles

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36
Q

A small change in the amplitude has what effect on intensity?

A

A small change in the amplitude will result in a larger change to the intensity

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37
Q

What is SP?

A

Spatial Average

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38
Q

What is the greatest intensity found across the beam called?

A

The spatial peak

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39
Q

What is SA?

A

The spatial average

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40
Q

What is spatial average?

A

The average intensity measured over the entire beam

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41
Q

What is TA?

A

Temporal Average

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42
Q

What temporal intensity includes the dead time between pulses where there is no intensity? (Ringing and listening time)

A

Temporal average

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43
Q

What is TP?

A

Temporal Peak

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44
Q

What is Temporal Peak?

A

The greatest amplitude found in the pulse at any given time

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45
Q

What is PA?

A

Pulse Average

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46
Q

What is the average for all values found in a pulse?

A

Pulse Average

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47
Q

What can PA be used interchangeably with? (Identical)

A

The temporal peak

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48
Q

What are the TP and TA related by?

A

The duty factor

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49
Q

What are SP and SA related by?

A

The BUR

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50
Q

What is BUR?

A

Beam Uniformity Ratio

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51
Q

What is the formula for BUR?

A

BUR = SP/SA

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52
Q

What is the formula for DF? And what is the MORE accurate formula?

A

DF = TA/TP

DF = TA/PA

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53
Q

What is slightly greater, TA or PA?

A

TA

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54
Q

In space where is the SA and SP found?

A

The SA is found at the transducer face and the SP is found at the focal point where the beam area is the smallest

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55
Q

What does BUR indicate?

A

How much focusing there is in a beam

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56
Q

What type of beams have high BUR?

A

Highly focused beams

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57
Q

Weakly focused beams have what type of BUR?

A

Low BUR

58
Q

Can the BUR ever be less than one?

A

No because peaks are always higher than averages so BUR will always be greater than one (BUR = SP/SA)

59
Q

How much BUR would a perfectly uniform beam have?

A

BUR of one

60
Q

Why do beams always have a natural focus?

A

Because the BUR will always be greater than one

61
Q

When BUR = 1, what is the shape of the beam?

A

Straight

62
Q

How does tightening the focus effect BUR?

A

Increases BUR

63
Q

What factors will increase Spatial Peak?

A

Increasing power or focus

64
Q

What factor increases spatial average?

A

Increasing power

65
Q

What effects area?

A

Aperture

66
Q

What factors effect temporal intensities?

A

An increase in power or an increase in the duty factor

67
Q

What factors increase DF?

A

An increase in PRF or an increase in the pulse duration

68
Q

What is the formula for pulse duration?

A

PD = Period x Ringdown

69
Q

What is PRP?

A

Pulse Repitition Period (Go return time)

70
Q

What is the DF for continuous wave?

A

100% since the crystal is constantly ringing

71
Q

How do you find DF as a percentage?

A

DF = PD/PRP x 100%

72
Q

Does CW or PW have a higher SPTA value?

A

CW because the crystal is always ringing

73
Q

What is the decimal number of 100?

A

1

74
Q

From highest to lowest, what are the intensities?

A 
SPTP
SPPA
SPTA
SATP
SAPA
SATA
75
Q

Why is SPTA used?

A

Because the highest intensity is only on for a fraction of a second, SPTA is more fair because it is averaged over the listening and ringing time.

76
Q

What is SPTP also known as?

A

The instantaneous peak (i.p.)

77
Q

What are the other names for SPPA?

A

Maximum intensity (i.m.)
Or:
Time averaged half maximum

78
Q

What sources do our info about US bioeffects come from?

A
  1. Epidemiology
  2. In vitro cell studies
  3. Animal studies
79
Q

What are in vivo studies?

A

Animal studies

80
Q

What is AIUM?

A

American Institute of Ultrasound is a resource for bioeffects

81
Q

What is the name for a study conducted over a long period of time?

A

Epidemiologic study

82
Q

How are US epidemiologic studies conducted?

A

People who were exposed to US in-utero are monitored over several years in order to look for cause and effect.

83
Q

What is the conclusion of epidemiological studies for OB US?

A

No evidence of insufficienct low birth weight, delayed speech, dyslexia and non-right-handedness.

84
Q

What does an in vitro study do?

A

Exposes macromolecules, membrane transport systems, cells or clumps of cells suspended in liquid to US.

85
Q

What are the results of in vitro studies?

A

It is difficult to say that an effect on cells will have a direct clinical significance but in vitro studies can give valuable info to set thresholds for in vivo studies

86
Q

What bioeffects have in vivo studies shown potential for? (6)

A
  • Fetal weight reduction
  • Postpartum mortality
  • Fetal abnormalities
  • Tissue lesions
  • Hind limb paralysis
  • Blood flow stasis (clots)
87
Q

What positive bio effects have been reported during in vivo studies?

A

Wound repair enhancement and tumor regression

88
Q

What intensities are considered safe for an unfocused probe?

A

Intensities below 100 mW/cm squared

89
Q

What intensities are considered safe for a focused probe?

A

Intensities below 1000 mW/cm squared

90
Q

What is the difference in threshold between focused and unfocused probes?

A

It is 10x greater for focused probes

91
Q

What are the two main categories of bioeffects?

A
  1. Thermal

2. Non-thermal (mechanical)

92
Q

What is absorption?

A

The conversion of heat to sound

93
Q

What is attenuation primarily due to?

A

Absorption 80%

94
Q

When are there no adverse thermal effects?

A

When the temperature increase is less than two degrees Celsius

95
Q

At what temperature do adverse effects start occurring?

A

Over 6 degrees but only if the exposure time is over 16 minuets

96
Q

What do adverse effects of increased temperature depend on in order to occur?

A

Longer exposure time gives a higher chance of adverse effects at higher temps

97
Q

What are the types of mechanical effects?

A
  1. Radiation force

2. Cavitation

98
Q

What is radiation force?

A

The force exerted by sound on the medium which can deform and disrupt structures

99
Q

What can radiation force cause?

A

Flow in absorbing fluids resulting in shear forces

100
Q

What are shear forces?

A

Compression forces that force one part of the body in one direction and another in the opposite direction

101
Q

What is cavitation?

A

The production and behaviour of bubbles in a liquid medium

102
Q

How can cavitation be divided?

A

Stable cavitation and transient cavitation

103
Q

What is stable cavitation?

A

Simple oscillation of the bubbles that can result in the streaming of liquid resulting in shear stresses

104
Q

What is transient cavitation?

A

When the bubble actually collapses producing shock waves

105
Q

What can the shock waves from transient cavitation result in?

A

Localized extremely high temps and can even emit light in clear fluids

106
Q

What happened in 1992 regarding US and bioeffects?

A

A standard was set so that realtime info relating to the potential for bioeffects is displayed on the monitor

107
Q

What is ODS?

A

Output Display Standard - the quantities relating to bio effect potential that are displayed on the US monitor.

108
Q

What quantities are displayed for ODS?

A
  1. Thermal Index (TI)

2. Mechanical Index (MI)

109
Q

What is thermal index?

A

The ratio of acoustical power produced by the transducer to the power required to raise the temp in tissue by 1 degree celcius

110
Q

A TI value of 1 means what?

A

That under assumed tissue conditions, a TI of 1 could POSSIBLY raise the temp of the tissue by 1 Degree celsius

111
Q

How is TI further divided?

A

TIS
TIB
TIC

112
Q

What is the most common type of TI?

A

TIS

113
Q

What is TIS used for?

A

Soft tissue

114
Q

What is TIB used for?

A

Bone near the focus, used for OB scanning

115
Q

What is TIC?

A

Bone near the surface (ex. Transcranial)

116
Q

What is TI divided into TIS,TIB, and TIS?

A

To account for the different tissue types and their respective absorption rates

117
Q

What does Mechanical Index represent?

A

The likelihood that the energy used will lead to cavitation

118
Q

What is the MI proportional to?

A

The peak rarefactional pressure

119
Q

If the rarefactional pressure doubles, what happens to the MI?

A

Its proportional so the MI will double as well.

120
Q

What is the MI inversely proportional to?

A

The square root of the frequency

121
Q

If the MI reduced to half what happend to the frequency?

A

It quadrupled

122
Q

In what cases could the TI and MI be underestimated?

A

In the presence of a large fluid collection (but these situations usually allow for less power).

123
Q

What is important to consider as TI rises?

A

The exposure time

124
Q

What is max TI?

A

6

125
Q

What is max MI?

A

1.9

126
Q

What is the specific SPTA allowed for Cardiac, peripheral vasc, ophthalmic, fetal and other exams?

A

Cardiac = 430
Fetal and other = 94
Periph Vasc = 20
Ophthalmic = 17

127
Q

What are the typical output intensities (SPTA) from US scanners?

A 
B-Scan = 18.7
M-mode = 73
CW = 1140
Doppler = 234
128
Q

How can the diff applications of US be divided?

A

Scanned and non-scanned

129
Q

What are the non-scanned types? (3)

A
  1. CW
  2. Pulsed Doppler
  3. M-mode `
130
Q

What type of US application poses the highest risk of for thermal effects and why?

A

Non-scanned, due to the fact that they transmit repeatedly in a straight line

131
Q

What US application poses the biggest risk for thermal effects?

A

CW

132
Q

Why are contrast agents concerning?

A

Recent studies show that gas bodies present in circulation can produce non-thermal adverse effects even when intensities are below threshold

133
Q

Regarding contrast, at what MI value is there little risk?

A

MI below 0.4

134
Q

What are the adverse effects of contrast?

A
  1. Induction of premature ventricular contractions
  2. Microvascular leakage with petechiae
  3. Glomerular capillary hemorrhage
  4. Local cell killing
135
Q

What are petechiae?

A

Tiny dots on the skin caused by bleeding

136
Q

What is important for practitioners to be aware of when using contrast?

A
  1. Use minimal agent dose
  2. MI
  3. Examination time
137
Q

What is ALARA?

A

As Low As Reasonably Achievable

138
Q

What does ALARA mean?

A

The principle of keeping US exposure minimal while optimizing diagnostic information

139
Q

What activities should US not be used for under Health Canada guidelines?

A
  1. To have a pic of fetus for non-medical reasons
  2. To learn the sex of the fetus for non- medical reasons
  3. For commercial purposes (trade shows or producing pics, videos of the fetus).
140
Q

What are the 4 different restricted acts that sonographers will be required to perform once Alberta is self regulated?

A
  1. OBS scans
  2. EV’s
  3. Contrast
  4. IV’s
141
Q

Once self regulation is finalized what will Alberta sonographers fall under?

A

ACMDTT

PHYS 314 (5 decks)

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