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Phys 314 Physics 3 > Bioeffects > Flashcards

Bioeffects Flashcards

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1
Q

What are bio effects?

A

The potential biological effects that can occur when ultrasound propagates through the body

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2
Q

What is the risk of ultrasound in terms of bio effects?

A

Lots of research has been done, virtually all ultrasound induced adverse bio effects occur at higher intensities than diagnostic ultrasound

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3
Q

What are the three ways in which we can describe the strength of the wave?

A
  1. Amplitude
  2. Power
  3. Intensity
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4
Q

Amplitude, power, and intensity are 3 ways to describe the strength of a wave. However, these can also express what other things?

A

Loudness or volume of sound

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5
Q

Amplitude is defined as what? 3

A
  1. Particle displacement
  2. Particle velocity
  3. Acoustic pressure of a sound wave
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6
Q

Amplitude indicates what?

A

The strength of the detected echo or the voltage induced in a crystal by a pressure wave

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7
Q

What is another way to describe amplitude? 2

A
  1. Maximum displacement
  2. Acoustic variable
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8
Q

What determines the initial amplitude of a pulse?

A

Pulser

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9
Q

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

A

Attenuation

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10
Q

What are the 5 mechanisms that cause attenuation?

A
  1. Absorption
  2. Reflection
  3. Scatter
  4. Refraction
  5. Wave front divergence
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11
Q

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

A

Yes it does, attenuation happens on the way back

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12
Q

What is the measure of power?

A

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

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13
Q

The absolute unit of power is what?

A

Watt

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14
Q

What is the relative unit for power?

A

dB

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15
Q

Since power is another expression of strength, just like the amplitude, it is determined by what?

A

The Pulser

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16
Q

Power defaults to what amount, relative to what?

A

100%

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17
Q

Intensity is a measure of what?

A

The strength of sound wave and is equal to the power per unit area

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18
Q

What is the formula for intensity?

A

Intensity = power/ area

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19
Q

What is the absolute unit of intensity?

A

mW/Cm or W/cm

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20
Q

What is the relative units for intensity?

A

dB

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21
Q

If power increase what happens to the intensity?

A

It also increases

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22
Q

If the area decreases what happens to the intensity?

A

It increases (use the intensity formulas)

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23
Q

What is the relationship of intensity and amplitude?

A
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24
Q

what are four different expressions of intensity?

A
  1. Spatial peak
  2. Spatial average
  3. Temporal average
  4. Temporal peak
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25
Q

Where is the spatial average and peak found on the transducer?

A

The spatial average is found at the transducer face and the peak is found at the focal point

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26
Q

What is Spatial peak and average related to?

A

Beam uniformity ratio

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27
Q

What is the BUR ratio?

A

BUR = SP/SA

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28
Q

The beam uniformity ratio gives an idea of what?

A

How much focusing there is in a beam

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29
Q

Highly focused beams have what BUR value?

A

High

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30
Q

Weakly focused beams have what BUR value?

A

Low

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31
Q

Why is BUR always greater than 1?

A

Peaks are always higher than averages (in terms of spatial)

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32
Q

A perfectly uniform beam will have what BUR value?

A

one

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33
Q

The factor that effects the spatial intensities in an ultrasound system are what? 2

A
  1. Spatial peak will increase with an increase in power or focusing
  2. Spatial average will increase with an increase in power
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34
Q

Over the time a pulse is generated there is a temporal average which includes what?

A

Both the ringing and listening phase of the pulse and the temporal peak which is the highest amplitude in the pulse at any given time

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35
Q

Temporal peak and temporal average are related how?

A

Duty factor

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36
Q

What is the ratio for Duty factor?

A

DF = TA/TP

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37
Q

The factors that effect temporal intensities are what?

A

An increase in power or an increase in they duty factor

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38
Q

Duty factor is increased if what happens?

A

The PRF or the pulse duration is increased

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39
Q

The duty factor for CW is what? What does this mean?

A
  1. 100% because the crystal is constantly ringing
  2. CW typically has a higher SPTA value than pulsed wave applications
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40
Q

What is SPTP also known as?

A

Instantaneous peak

41
Q

SPPA intensity is also known as what?

A

The maximum intensity, or time averaged half maximum

42
Q

The information that we have on the effects of ultrasound come from multiple sources, what are three?

A
  1. Epidemiology
  2. In vitro cell studies
  3. Animal studies
43
Q

What is an extensive resource for bio effects information?

A

American institute of ultrasound in medicine
(AIUM)

44
Q

What is an epidemiological study?

A

Study conducted over a long term

45
Q

Intensities below what value is considered safe for an unfocused probe?

A

100 mW/cm

46
Q

Intensities below what value is considered safe for focused probes?

A

1000 mW/cm

47
Q

Bio effects can be divided into two main categories, what are they?

A
  1. Thermal
  2. Non- thermal
48
Q

When dealing with thermal effects, it is important to remember that attenuation is primarily due to what?

A

Absorption which is the conversion of sound to heat

49
Q

Temperature can increase with an increase in what?

A

Frequency or intensity

50
Q

Can temperature increase from B-mode to Colour doppler to spectral doppler?

A

Yes

51
Q

Does adult tissues handle temperature the same as neonatal?

A

No, adults handle it better

52
Q

How many bioeffects are attributed to hyperthermia?

A

Over 80 known

53
Q

In terms of hyperthermia and bioeffects, there are no adverse effects when the temperature does not exceed what?

A

39 degrees

54
Q

The temperature rise near bone is what compared to soft tissue?

A

Significantly higher

55
Q

Temperature rise is most detrimental during what phase?

A

Organogenesis (first trimester)

56
Q

In terms of bioeffects, there are not adverse effects when temperature index is where?

A

Between 1.5 - 6, depending on exposure time

57
Q

The longer the exposure time the more chance of what?

A

Adverse effects at higher temperature

58
Q

A significant rise in temperature is in excess of what?

A

1.5 degrees Celsius

59
Q

Mechanical effects include what?

A

Radiation force and cavitation

60
Q

Radiation force is what?

A

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

61
Q

Radiation force can cause what?

A

Flow in absorbing fluids resulting in shear forces

62
Q

Cavitation is what?

A

The production and behaviour of bubbles in a liquid medium

63
Q

Cavitation can be divided into what categories?

A

Stable and transient

64
Q

Stable cavitation is what?

A

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

65
Q

Transient cavitation is what?

A

When the bubble actually collapses producing shock waves

66
Q

In transient cavitation, the shock waves can result in what?

A

Localized extremely high temperatures and has even emitted light in clear fluids

67
Q

When was the standard for bioeffects created?

A

1992

68
Q

ODS is what? What is displayed? 2

A
  1. Output display standard
  2. Thermal index and mechanical index
69
Q

What is Thermal index?

A

The ratio of acoustical power produced by the transducer to the power required to raise the temperature in tissue 1 degrees Celsius

70
Q

A TI value of 1, under assumed tissue conditions, could possible do what?

A

Raise temperature of tissue by 1 degrees Celsius

71
Q

TI is further divided into 3 categories, what are they?

A
  1. TIS
  2. TIB
  3. TIC
72
Q

What is TIS?

A

It for soft tissue and is the most common

73
Q

What is TIB?

A

For bone near the focus ad is used for obstetrical scanning

74
Q

What is TIC?

A

For bone near the surface as in the case of a transcranial study

75
Q

Mechanical index represents what?

A

The likelihood that energy used will lead to cavitation

76
Q

The MI is proportional to what?

A

The peak rarefactional pressure, so if the pressure doubles then the MI doubles as well

77
Q

The MI is inversely proportional to what?

A

The square root of the frequency, so the frequency would have to quadruple for the MI to halve

78
Q

TI max is what? And what is MI max?

A

6 and 1.9

79
Q

What increases the possibility for MI an TI to be underestimated?

A

Prescience of large fluid collection, but these situation usually allows for less power

80
Q

As the TI increases it is prudent to consider what?

A

The exposure times

81
Q

What is the SPTA limits for Cardiac, peripheral vascular, ophthalmic, fetal and other?

A
82
Q

What is the SPTA value for Pulsed doppler?

A

1140

83
Q

The different applications of ultrasound can be divided into what different categories?

A

Scanned and non scanned types

84
Q

The non scanned applications are what? 3

A
  1. CW
  2. Pulsed doppler
  3. M- mode
85
Q

What poses the highest risk for bio effects, why?

A
  1. Non scanned applications
  2. Thermal effects with CW having the most potential due to the fact they transmit repeatedly in a straight line
86
Q

Recent studies have concluded that adverse non-thermal effects may occur when?

A

When gas bodies are present in circulation

87
Q

Do contrast agents in the blood stream pose any kind of concern? Why?

A

Yes, recent studies confirmed that at intensity below the accepted threshold, adverse non-thermal effects may occur when gas bodies are present

88
Q

When MI values are below 0.4 what happens?

A

There is little risk

89
Q

In terms of bioeffects adverses effects have included what 4 things?

A
  1. The induction of premature ventricular contraction
  2. Micro vascular leakage with petechiae
  3. Glomerular capillary hemorrhage
  4. Local cell killing
90
Q

Medical significance is uncertain so what does this mean?

A

Prudent use is required

91
Q

When imaging with contrast agents, practitioners should do what? 3

A
  1. Use the minimal agent dose
  2. MI
  3. Examination time consistent with efficacious acquisition of diagnostic information
92
Q

Although the benefits of ultrasound outweigh the risk, one must consider the risk of using what?

A

Suboptimal equipment or having the exam performed by a poorly trained operator

93
Q

The balance between benefit and risk comes with the prudent use of ultrasound apply to what concept?

A

ALARA

94
Q

What does ALARA stand form?

A

As low as reasonably achievable

95
Q

Following ALARA principles we keep ultrasound exposure what?

A

Minimized while optimizing diagnostic information

96
Q

Who established the guidelines for the safe use of diagnostic medicine?

A

Heath Canada

97
Q

Guidelines state that the use of ultrasound should not be used for what 3 things?

A
  1. To have a picture of a fetus, solely for non-medical reasons
  2. To learn the sex of the fetus, solely for non-medical reasons
  3. For commercial purposes, such as trade shows or producing pictures or videos of the fetus
98
Q

What is the ACMDTT?

A

Where sonographers fall after regulation

Phys 314 Physics 3 (11 decks)

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