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Chapter 24 Flashcards

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1
Q

Hydrophone is similar to

A

a small hypodermic needle with a tiny piece of piezoelectric material attached to its end

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2
Q

_ is a microprobe

A

hydrophone

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3
Q

We want to know the output of the machine because_

A

the majority of sound energy that goes into the patient stays there. We need to know if there are potential bioeffects that are going to harm the patient in the process.

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4
Q

Hydrophone: a wire connects _ to _

A

the PZT to an oscilloscope

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5
Q

Hyrophone is placed in the _ created by _

A

sound beam created by the transducer

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6
Q

A voltage from the hydrophone relates to the _ and is displayed in the _

A

sound beams pressure.

oscilloscope

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7
Q

Hydrophone: The acoustic pressure is measures at

A

specific locations within the sound beam

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8
Q

By moving the hydrophone to numerous locations while measuring the acoustic pressure, one can determine

A

the sound beams shape

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9
Q

How do you determine the sound beams shape?

A

By moving the hydrophone to numerous locations

while measuring the acoustic pressure

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10
Q

Hydrophone also measures _

A

period, PRP, PRF, and pulse duration

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11
Q

Hydrophones may be calibrates, that provides a known relationship between _

A

the acoustic pressure signal and the voltage created by the PZT.

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12
Q

In general, transducer output is lowest when

performing _ and highest when performing _

A

gray scale imaging, doppler

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13
Q

Another form of hydrophone is constructed from

A

a very thin membrane of piezoelectric plastic.

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14
Q

Hydrophone: Only _ is

pressure sensitive

A

a very small area in the

center of the membrane

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15
Q

_ force : A transducer’s sound beam creates a very

small force on any target that it strikes.

A

Radiation

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16
Q

Radiation force: the target can be _ or _ and act as a _

A

a balance, a float, scale to measure the force from the sound beam

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17
Q

Radiation force: the measured force relates to _

A

the power in the beam

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18
Q

Radiation force AKA

A

feedback microbalance

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19
Q

Acousto-Optics are based on

A

the interaction of sound and light

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20
Q

A shadowing system that
allows us to view the shape of a sound beam in a
medium.

A

Schlieren

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21
Q

Absorption is

A

the conversion of sound energy

into heat

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22
Q

Three devices measure the output of

ultrasound transducers by absorption

A
  1. Calorimeter
  2. Thermocouple
  3. Liquid crystal
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23
Q

Calorimeter measures

A

the total power in a sound beam through the process of absorption

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24
Q

Calorimeter: The sound beam is directed into the calorimeter where the sound energy is

A

converted into heat

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25
Q

Calorimeter: the sound beams total power is calculated by

A

measuring the temperature rise and the time of heating.

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26
Q

Tiny electronic thermometer

A

Thermocouple

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27
Q

A dab of absorbing material is placed on the

thermocouple and it is inserted into _ and _ is measured

A

the sound beam, temperature

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28
Q

Thermocouple: the temperature rise is related to

A

the power of
the sound beam at the particular location
where the device is positioned.

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29
Q

Certain liquid crystals change color based on

A

their temperature

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30
Q

Liquid crystals: when a sound beam strikes the crystals, the sound energy is _

A

absorbed

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31
Q

Liquid crystals: the change in crystal temperature causes a changes in their color, providing insight into _

A

the shape and strength of the sound beam.

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32
Q

The benefits to the patient must outweigh

A

the risks of

the exam

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33
Q

Low intensity ultrasound has _ bioeffects

A

no known

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34
Q

_ ultrasound intensities damage biologic

tissues

A

Extremely high

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35
Q

there are _ cases of diagnostic imaging at standard intensities in the
absence of contrast agents resulting in biological effects and tissue injury.

A

no known

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36
Q

Under_ circumstances, bioeffects are

beneficial. Example, _

A

controlled.

Therapeutic ultrasound for muscular injury

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37
Q

The science of identifying and measuring the

characteristics of an ultrasound beam that are relevant to its potential for producing biologic effects

A

Dosimetry

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38
Q

Dosimetry

A

The science of identifying and measuring the

characteristics of an ultrasound beam that are relevant to its potential for producing biologic effects

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39
Q

Bioeffects research may be conducted in two broad

areas:

A

in vivo and in vitro

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40
Q

In vivo

A

within the living body of an animal or a plant

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41
Q

In vitro

A

outside the living body/in an artificial

environment

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42
Q

n vitro research indicates that _ intensities can cause genetic damage and cell
death.

A

very high

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43
Q

AIUM Statement on In Vitro

Bioeffects

A

In vitro bioeffects research is important
In vitro bioeffects are real even though they may not apply to to the clinical setting
In vitro bioeffect research that claims direct clinical significance (without in vivo validation) should be viewed with caution

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44
Q

There are two techniques used to study bioeffects:

A

Mechanistic approach

Empirical approach

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45
Q

_ approach begins as a proposal that a
specific mechanism has the potential to produce
bioeffects. Based on that proposal, a theoretical
analysis is performed to estimate the scope of the
bioeffects at various exposure levels. Searches for a relationship between cause and effect.

A

Mechanistic

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46
Q

Mechanistic approach

A

begins as a proposal that a
specific mechanism has the potential to produce
bioeffects. Based on that proposal, a theoretical
analysis is performed to estimate the scope of the
bioeffects at various exposure levels. Searches for a relationship between cause and effect.

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47
Q

_ approach – based on the acquisition and review of information from patients or animals exposed to ultrasound. The research seeks a relationship between the exposure to ultrasound and the effects of that exposure

A

Empirical

48
Q

Empirical approach

A

based on the acquisition and review of information from patients or animals
exposed to ultrasound. The research seeks a
relationship between the exposure to ultrasound
and the effects of that exposure.

49
Q

Mechanistic appraoch strenght:

A

Broad exposure range can be evaluated

50
Q

Mechanistic approach weaknesses:

A

uncertainty about assumptions, are other mechanisms involved?, is the bioeffect clinically significant?

51
Q

Empirical approach strenghts:

A

no need to undersand mechanisms, biological significance is obvious

52
Q

Empirical approach weakness:

A

No need to understand mechanisms, species differences may alter results

53
Q

The best studies are made when _

A

empirical and mechanistic approach agree.

54
Q

Two important bioeffects mechanisms are:

A
  1. Thermal

2. Cavitation (nonthermal)

55
Q

_ proposes that bioeffects result from tissue

temperature elevation.

A

thermal mechanisms

56
Q

The rationale for studying thermal effects are:

A

As sound propagates in the body, energy is
converted into heat.
Core temperature is regulated at 37° C. Life
processes may not function normally at other
temperatures.

57
Q

tissue temperatures are
elevated routinely in our daily lives (with or without)
adverse effects.

A

without

58
Q

The thermal index is a useful predictor of

A

maximum
temperature increase under most clinically relevant
conditions.

59
Q

Thermal indices are the best measurement or estimate of _

A

in vivo tissue temperature

60
Q

Thermal index is reported in three forms:

A

TIS
TIB
TIC

61
Q

TIS

A

soft tissue thermal index, assumes that sound is

traveling in soft tissue

62
Q

TIB

A

bone thermal index, assumes that bone is at or

near the focus of the sound beam

63
Q

TIC

A

cranial bone thermal index, assumes that cranial

bone is in the sound beam’s near field

64
Q

Thermal Mechanism –

Empirical Findings: Serious tissue damage occurs from

A

prolonged

and excessive elevation of tissue temperature

65
Q

Thermal Mechanism –
Empirical Findings: A _ rise in testicular temperature can
cause infertility.

A

2° to 4°

66
Q

Thermal Mechanism –

Empirical Findings: Tissue heating is related to

A

the output
characteristics of the transducer and the
properties of the tissues.

67
Q

Thermal Mechanism –

Empirical Findings: A combination of _ determine the likelihood of harmful bioeffects.

A

temperature and exposure

time

68
Q

Thermal Mechanism –

Empirical Findings: Maximal heating is related to the beam’s _ intensity

A

SPTA

69
Q

Thermal Mechanism –

Empirical Findings: SPTA: The current FDA regulatory limit is

A

720 mW/cm^2

70
Q

Thermal Mechanism –
Empirical Findings: No confirmed bioeffects have been reported for
temperature elevations of up to _ above
normal for exposures of _

A

2° C. less than 50 hours

71
Q

Thermal Mechanism –

Empirical Findings: Temperature elevations are greater with _ than _

A

Doppler

gray scale

72
Q

Thermal Mechanism –

Empirical Findings: Fetal and neonatal tissues appear (more or less) tolerant of tissue heating than adult tissues

A

less

73
Q 
Bone absorbs (more or less) acoustic energy than soft 
tissue.
A

more

74
Q

The temperature rise in soft tissues near bone is significantly _ than in other
locations.

A

higher

75
Q

Circumstances where ultrasound strikes _ deserve special attention.

A

fetal bone

76
Q

Thermal Mechanism –
Mechanistic Data: Theoretical models appear to correlate with
experimental data even though:

A

The ultrasound beam is quite complex
Diagnostic equipment is diverse
Tissue characteristics are different

77
Q

Nonthermal Mechanism consist of

A

cavitation and radiation force

78
Q

Radiation force –

A

exerted by a sound beam on tissues. Sheer stresses and streaming of fluids
can distort or disturb biologic structures

79
Q

Cavitation –

A

the interaction of sound waves with microscopic gas bubbles in the tissue

80
Q

Bubbles =

A

gaseous nuclei, found in tissues –

different from contrast agents

81
Q

The only cavitation bioeffect identified at
intensities typical of diagnostic ultrasound are
in tissues with

A

a well defined population of

stabilized gas bodies, such as lung

82
Q

Two forms of cavitation exist:

A

Stable and transient

83
Q

At lower MI levels, _ occurs

A

Stable cavitation

84
Q

Stable Cavitation: The gaseous nuclei tend to

A

oscillate (expand and contract)

85
Q

Stable Cavitation: Bubbles that are a few millimeters in diameter might _ but do not _

A

double in size,

burst

86
Q

Stable Cavitation: The bubbles intercept and absorb much of the

A

acoustic energy

87
Q

Stable Cavitation: The fluids surrounding the cells undergo

A

microstreaming and the cells are exposed to shear stresses.

88
Q

_ may occur with higher MI levels

A

transient cavitation

89
Q

Bubble bursting

A

transient cavitation

90
Q

Transient cavitation AKA

A

inertial or normal cavitation

91
Q

_ produces highly localized, violent effects including:
Colossal temperatures
Shock waves (enormous pressures)

A

Transient cavitation

92
Q

Are destructive effects or transient cavitation considered clinically important? Why or why not?

A

No, they are highly localized and only affect a few cells

93
Q

Stable or transient? Oscillating bubble, microstreaming and shear stresses, lower MI

A

Stable

94
Q

Stable or transient? AKA normal or inertial, bursting bubble, shock waves and very high temperatures, higher MI

A

Transient

95
Q

A calculated number related to the likelihood of harmful bioeffects from cavitation. Best indicator

A

Mechanical index

96
Q

MI is realted to 2 sound wave characteristics:

A

Peak rarefaction pressure and lower frequency

97
Q

Greater likelihood of cavitation bioeffects and a

higher MI with:

A

Additional negative pressure

Lower frequency

98
Q

A branch of medicine associated with

population studies

A

Epidemiology

99
Q

an exposure response method

which utilizes clinical surveys

A

Empirical

100
Q

When the occurrence of rate of bioeffects is

small, population studies require_.

A

many subjetcs.

101
Q

The smaller the effect, the _ it is to detect.

A

Harder

102
Q

Many epidemiologic studies deal with in utero

fetal exposures to ultrasound because:

A

A large percentage of pregnant women in the
U.S. are scanned
Ultrasound is routinely used during normal
pregnancies.
Harmful effects have the potential to affect the
fetus for life.

103
Q

Epidemiologic data indicate that ultrasound exposure (is or is not) associated with adverse fetal outcome.

A

is not

104
Q

Epidemiology limitations:

A

Retrospective – information is obtained from old medical records.
Ambiguities may exist in the data, such as
justification for the exam, gestational age,
number of scans, technique, and exposure time.
Risk factors other than exposure to ultrasound
may precipitate a bad outcome in the fetus.
(environmental factors, poor nutrition, smoking,
alcohol, or drug abuse)

105
Q

The best epidemiologic studies are:

A

Prospective and randomized

106
Q

Prospective

A

forward looking

107
Q

Randomized

A

creates 2 groups of patients, one group exposed to u/s and one group that is not.

108
Q

The conclusions of the AIUM include:

A

No confirmed harmful bioeffects from exposure
to diagnostic ultrasound have ever been reported
It is possible that bioeffects may be identified in the future
The benefits to the patient outweighs the risks
It is appropriate to use diagnostic ultrasound
prudently to provide benefit to the patient
It is inappropriate to use diagnostic ultrasound in
a non-medical setting for entertainment.
No confirmed bioeffects on patients or sonographers
have been found with the use of diagnostic ultrasound
Experience with diagnostic ultrasound may differ from research and training, due in part to longer research exams and greater exposure.
When used without direct medical benefit to the
patient, the subject should be informed how the
research study differs from standard diagnostic
procedures.

109
Q

Precautions such as _
should always be taken to avoid electrical
hazard

A

proper electrical grounding

110
Q

The greatest risk to the patient arises from

A

electrical shock from a cracked transducer

housing.

111
Q

_ is the primary determinant of patient exposure.

A

Exam time

112
Q

Use the _ output
power and _ amplification to optimize
image quality.

A

minimum, maximum

113
Q

No bioeffects are associated with MI below

A

.4

114
Q

tissue heating

A

thermal mechanism

115
Q

Radiations force and cavitation

A

Nonthermal mechanisms

116
Q

Streaming of fluid

A

motion of fluid due to radiation force

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