Chapter 24 Flashcards
(116 cards)
1
Q
Hydrophone is similar to
A
a small hypodermic needle with a tiny piece of piezoelectric material attached to its end
2
Q
_ is a microprobe
A
hydrophone
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.
4
Q
Hydrophone: a wire connects _ to _
A
the PZT to an oscilloscope
5
Q
Hyrophone is placed in the _ created by _
A
sound beam created by the transducer
6
Q
A voltage from the hydrophone relates to the _ and is displayed in the _
A
sound beams pressure.
oscilloscope
7
Q
Hydrophone: The acoustic pressure is measures at
A
specific locations within the sound beam
8
Q
By moving the hydrophone to numerous locations while measuring the acoustic pressure, one can determine
A
the sound beams shape
9
Q
How do you determine the sound beams shape?
A
By moving the hydrophone to numerous locations
while measuring the acoustic pressure
10
Q
Hydrophone also measures _
A
period, PRP, PRF, and pulse duration
11
Q
Hydrophones may be calibrates, that provides a known relationship between _
A
the acoustic pressure signal and the voltage created by the PZT.
12
Q
In general, transducer output is lowest when
performing _ and highest when performing _
A
gray scale imaging, doppler
13
Q
Another form of hydrophone is constructed from
A
a very thin membrane of piezoelectric plastic.
14
Q
Hydrophone: Only _ is
pressure sensitive
A
a very small area in the
center of the membrane
15
Q
_ force : A transducer’s sound beam creates a very
small force on any target that it strikes.
A
Radiation
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
17
Q
Radiation force: the measured force relates to _
A
the power in the beam
18
Q
Radiation force AKA
A
feedback microbalance
19
Q
Acousto-Optics are based on
A
the interaction of sound and light
20
Q
A shadowing system that
allows us to view the shape of a sound beam in a
medium.
A
Schlieren
21
Q
Absorption is
A
the conversion of sound energy
into heat
22
Q
Three devices measure the output of
ultrasound transducers by absorption
A
- Calorimeter
- Thermocouple
- Liquid crystal
23
Q
Calorimeter measures
A
the total power in a sound beam through the process of absorption
24
Q
Calorimeter: The sound beam is directed into the calorimeter where the sound energy is
A
converted into heat
25
Calorimeter: the sound beams total power is calculated by
measuring the temperature rise and the time of heating.
26
Tiny electronic thermometer
Thermocouple
27
A dab of absorbing material is placed on the
| thermocouple and it is inserted into _ and _ is measured
the sound beam, temperature
28
Thermocouple: the temperature rise is related to
the power of
the sound beam at the particular location
where the device is positioned.
29
Certain liquid crystals change color based on
their temperature
30
Liquid crystals: when a sound beam strikes the crystals, the sound energy is _
absorbed
31
Liquid crystals: the change in crystal temperature causes a changes in their color, providing insight into _
the shape and strength of the sound beam.
32
The benefits to the patient must outweigh
the risks of
| the exam
33
Low intensity ultrasound has _ bioeffects
no known
34
_ ultrasound intensities damage biologic
| tissues
Extremely high
35
there are _ cases of diagnostic imaging at standard intensities in the
absence of contrast agents resulting in biological effects and tissue injury.
no known
36
Under_ circumstances, bioeffects are
| beneficial. Example, _
controlled.
| Therapeutic ultrasound for muscular injury
37
The science of identifying and measuring the
| characteristics of an ultrasound beam that are relevant to its potential for producing biologic effects
Dosimetry
38
Dosimetry
The science of identifying and measuring the
| characteristics of an ultrasound beam that are relevant to its potential for producing biologic effects
39
Bioeffects research may be conducted in two broad
| areas:
in vivo and in vitro
40
In vivo
within the living body of an animal or a plant
41
In vitro
outside the living body/in an artificial
| environment
42
n vitro research indicates that _ intensities can cause genetic damage and cell
death.
very high
43
AIUM Statement on In Vitro
| Bioeffects
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
44
There are two techniques used to study bioeffects:
Mechanistic approach
| Empirical approach
45
_ 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.
Mechanistic
46
Mechanistic 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.
47
_ 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
Empirical
48
Empirical 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.
49
Mechanistic appraoch strenght:
Broad exposure range can be evaluated
50
Mechanistic approach weaknesses:
uncertainty about assumptions, are other mechanisms involved?, is the bioeffect clinically significant?
51
Empirical approach strenghts:
no need to undersand mechanisms, biological significance is obvious
52
Empirical approach weakness:
No need to understand mechanisms, species differences may alter results
53
The best studies are made when _
empirical and mechanistic approach agree.
54
Two important bioeffects mechanisms are:
1. Thermal
| 2. Cavitation (nonthermal)
55
_ proposes that bioeffects result from tissue
| temperature elevation.
thermal mechanisms
56
The rationale for studying thermal effects are:
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
tissue temperatures are
elevated routinely in our daily lives (with or without)
adverse effects.
without
58
The thermal index is a useful predictor of
maximum
temperature increase under most clinically relevant
conditions.
59
Thermal indices are the best measurement or estimate of _
in vivo tissue temperature
60
Thermal index is reported in three forms:
TIS
TIB
TIC
61
TIS
soft tissue thermal index, assumes that sound is
| traveling in soft tissue
62
TIB
bone thermal index, assumes that bone is at or
| near the focus of the sound beam
63
TIC
cranial bone thermal index, assumes that cranial
| bone is in the sound beam’s near field
64
Thermal Mechanism –
| Empirical Findings: Serious tissue damage occurs from
prolonged
| and excessive elevation of tissue temperature
65
Thermal Mechanism –
Empirical Findings: A _ rise in testicular temperature can
cause infertility.
2° to 4°
66
Thermal Mechanism –
| Empirical Findings: Tissue heating is related to
the output
characteristics of the transducer and the
properties of the tissues.
67
Thermal Mechanism –
| Empirical Findings: A combination of _ determine the likelihood of harmful bioeffects.
temperature and exposure
| time
68
Thermal Mechanism –
| Empirical Findings: Maximal heating is related to the beam’s _ intensity
SPTA
69
Thermal Mechanism –
| Empirical Findings: SPTA: The current FDA regulatory limit is
720 mW/cm^2
70
Thermal Mechanism –
Empirical Findings: No confirmed bioeffects have been reported for
temperature elevations of up to _ above
normal for exposures of _
2° C. less than 50 hours
71
Thermal Mechanism –
| Empirical Findings: Temperature elevations are greater with _ than _
Doppler
| gray scale
72
Thermal Mechanism –
| Empirical Findings: Fetal and neonatal tissues appear (more or less) tolerant of tissue heating than adult tissues
less
73
```
Bone absorbs (more or less) acoustic energy than soft
tissue.
```
more
74
The temperature rise in soft tissues near bone is significantly _ than in other
locations.
higher
75
Circumstances where ultrasound strikes _ deserve special attention.
fetal bone
76
Thermal Mechanism –
Mechanistic Data: Theoretical models appear to correlate with
experimental data even though:
The ultrasound beam is quite complex
Diagnostic equipment is diverse
Tissue characteristics are different
77
Nonthermal Mechanism consist of
cavitation and radiation force
78
Radiation force –
exerted by a sound beam on tissues. Sheer stresses and streaming of fluids
can distort or disturb biologic structures
79
Cavitation –
the interaction of sound waves with microscopic gas bubbles in the tissue
80
Bubbles =
gaseous nuclei, found in tissues –
| different from contrast agents
81
The only cavitation bioeffect identified at
intensities typical of diagnostic ultrasound are
in tissues with
a well defined population of
| stabilized gas bodies, such as lung
82
Two forms of cavitation exist:
Stable and transient
83
At lower MI levels, _ occurs
Stable cavitation
84
Stable Cavitation: The gaseous nuclei tend to
oscillate (expand and contract)
85
Stable Cavitation: Bubbles that are a few millimeters in diameter might _ but do not _
double in size,
| burst
86
Stable Cavitation: The bubbles intercept and absorb much of the
acoustic energy
87
Stable Cavitation: The fluids surrounding the cells undergo
microstreaming and the cells are exposed to shear stresses.
88
_ may occur with higher MI levels
transient cavitation
89
Bubble bursting
transient cavitation
90
Transient cavitation AKA
inertial or normal cavitation
91
_ produces highly localized, violent effects including:
Colossal temperatures
Shock waves (enormous pressures)
Transient cavitation
92
Are destructive effects or transient cavitation considered clinically important? Why or why not?
No, they are highly localized and only affect a few cells
93
Stable or transient? Oscillating bubble, microstreaming and shear stresses, lower MI
Stable
94
Stable or transient? AKA normal or inertial, bursting bubble, shock waves and very high temperatures, higher MI
Transient
95
A calculated number related to the likelihood of harmful bioeffects from cavitation. Best indicator
Mechanical index
96
MI is realted to 2 sound wave characteristics:
Peak rarefaction pressure and lower frequency
97
Greater likelihood of cavitation bioeffects and a
| higher MI with:
Additional negative pressure
| Lower frequency
98
A branch of medicine associated with
| population studies
Epidemiology
99
an exposure response method
| which utilizes clinical surveys
Empirical
100
When the occurrence of rate of bioeffects is
| small, population studies require_.
many subjetcs.
101
The smaller the effect, the _ it is to detect.
Harder
102
Many epidemiologic studies deal with in utero
| fetal exposures to ultrasound because:
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
Epidemiologic data indicate that ultrasound exposure (is or is not) associated with adverse fetal outcome.
is not
104
Epidemiology limitations:
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
The best epidemiologic studies are:
Prospective and randomized
106
Prospective
forward looking
107
Randomized
creates 2 groups of patients, one group exposed to u/s and one group that is not.
108
The conclusions of the AIUM include:
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
Precautions such as _
should always be taken to avoid electrical
hazard
proper electrical grounding
110
The greatest risk to the patient arises from
electrical shock from a cracked transducer
| housing.
111
_ is the primary determinant of patient exposure.
Exam time
112
Use the _ output
power and _ amplification to optimize
image quality.
minimum, maximum
113
No bioeffects are associated with MI below
.4
114
tissue heating
thermal mechanism
115
Radiations force and cavitation
Nonthermal mechanisms
116
Streaming of fluid
motion of fluid due to radiation force
