Bioeffects, Safety And Power Flashcards
(141 cards)
1
Q
What is acoustic propagation?
A
The effect tissue has on sound
2
Q
What factor is important to note about all ultrasound-induced adverse bioeffects?
A
They have occurred at higher intensities than diagnostic US.
3
Q
When can potential biological effects occur?
A
When US propagates through human tissue
4
Q
How can the strength of a wave be described and what are the three ways?
A
(The loudness/Volume)
- Amplitude
- Power
- Intensity
5
Q
How are power and intensity related?
A
Directly/Proportional
If power increases so does intensity
6
Q
What is the formula for intensity?
A
Intensity = Power/Area
7
Q
What is amplitude?
A
The particle displacement, particle velocity or acoustic pressure of a sound wave.
8
Q
What is the maximum displacement of an acoustic variable?
A
Amplitude
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
10
Q
What determines the initial amplitude of a pulse?
A
The pulser sends an amplitude of voltage to make the crystal ring.
11
Q
As the pulse travels through the medium, what is the reduction in amplitude called?
A
Attenuation
12
Q
What are the 5 mechanisms of attenuation?
A
- Absorption
- Reflection
- Refraction
- Scatter
- Wave front divergence
13
Q
Does the amplitude of the echo decrease as the echo returns to the transducer?
A
Yes
14
Q
How does intensity change?
A
In time and space
15
Q
What is absorption?
A
80% of sound is attenuated by being converted to heat
16
Q
Study ‘Particle Motion’ and ‘Attenuation’ cards
A
….
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
18
Q
What is the formula for power?
A
Power = Intensity x Area
19
Q
What is the absolute unit of power?
A
The watt (joules per second)
20
Q
What is the relative unit of power?
A
Decibels (dB)
21
Q
Look over the I, P, V (10log, 10log, 20l0g) stuff….
A
…
22
Q
What determines the power?
A
The pulser does because power is an expression of strength
23
Q
What does power default to?
A
100% or 0 dB and is relative to the exam being performed
24
Q
In order from highest to lowest, what scanners have the highest output power? (SPTA)
A
- Pulsed Wave
- Colour Doppler
- B-Scan
- M-mode
25
Is the beam swept in PW?
No it is not swept unlike B Scan
26
What is intensity?
The measure of the strength of a sound wave
27
What is intensity equal to?
The power per unit area
28
What is the formula for intensity?
Intensity = Power/Area
29
What is the absolute unit of intensity?
mW/cm squared
OR
W/cm squared
30
What is the relative unit of intensity?
The decibel (dB)
31
What is the relationship between area and intensity?
Inversely proportional
If area decreases then intensity increases
32
Besides power, what else is intensity proportional to?
Intensity is proportional to the square of the pressure amplitude
I = amp^2
33
How does doubling the amplitude effect intensity?
Quadruples it
34
What determines the intensity coming out of the probe?
The amplitude of voltage
35
What happens to the intensity if the area is halved?
If the area is halved, the intensity doubles
36
A small change in the amplitude has what effect on intensity?
A small change in the amplitude will result in a larger change to the intensity
37
What is SP?
Spatial Average
38
What is the greatest intensity found across the beam called?
The spatial peak
39
What is SA?
The spatial average
40
What is spatial average?
The average intensity measured over the entire beam
41
What is TA?
Temporal Average
42
What temporal intensity includes the dead time between pulses where there is no intensity? (Ringing and listening time)
Temporal average
43
What is TP?
Temporal Peak
44
What is Temporal Peak?
The greatest amplitude found in the pulse at any given time
45
What is PA?
Pulse Average
46
What is the average for all values found in a pulse?
Pulse Average
47
What can PA be used interchangeably with? (Identical)
The temporal peak
48
What are the TP and TA related by?
The duty factor
49
What are SP and SA related by?
The BUR
50
What is BUR?
Beam Uniformity Ratio
51
What is the formula for BUR?
BUR = SP/SA
52
What is the formula for DF? And what is the MORE accurate formula?
DF = TA/TP
DF = TA/PA
53
What is slightly greater, TA or PA?
TA
54
In space where is the SA and SP found?
The SA is found at the transducer face and the SP is found at the focal point where the beam area is the smallest
55
What does BUR indicate?
How much focusing there is in a beam
56
What type of beams have high BUR?
Highly focused beams
57
Weakly focused beams have what type of BUR?
Low BUR
58
Can the BUR ever be less than one?
No because peaks are always higher than averages so BUR will always be greater than one (BUR = SP/SA)
59
How much BUR would a perfectly uniform beam have?
BUR of one
60
Why do beams always have a natural focus?
Because the BUR will always be greater than one
61
When BUR = 1, what is the shape of the beam?
Straight
62
How does tightening the focus effect BUR?
Increases BUR
63
What factors will increase Spatial Peak?
Increasing power or focus
64
What factor increases spatial average?
Increasing power
65
What effects area?
Aperture
66
What factors effect temporal intensities?
An increase in power or an increase in the duty factor
67
What factors increase DF?
An increase in PRF or an increase in the pulse duration
68
What is the formula for pulse duration?
PD = Period x Ringdown
69
What is PRP?
Pulse Repitition Period (Go return time)
70
What is the DF for continuous wave?
100% since the crystal is constantly ringing
71
How do you find DF as a percentage?
DF = PD/PRP x 100%
72
Does CW or PW have a higher SPTA value?
CW because the crystal is always ringing
73
What is the decimal number of 100?
1
74
From highest to lowest, what are the intensities?
```
SPTP
SPPA
SPTA
SATP
SAPA
SATA
```
75
Why is SPTA used?
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
What is SPTP also known as?
The instantaneous peak (i.p.)
77
What are the other names for SPPA?
Maximum intensity (i.m.)
Or:
Time averaged half maximum
78
What sources do our info about US bioeffects come from?
1. Epidemiology
2. In vitro cell studies
3. Animal studies
79
What are in vivo studies?
Animal studies
80
What is AIUM?
American Institute of Ultrasound is a resource for bioeffects
81
What is the name for a study conducted over a long period of time?
Epidemiologic study
82
How are US epidemiologic studies conducted?
People who were exposed to US in-utero are monitored over several years in order to look for cause and effect.
83
What is the conclusion of epidemiological studies for OB US?
No evidence of insufficienct low birth weight, delayed speech, dyslexia and non-right-handedness.
84
What does an in vitro study do?
Exposes macromolecules, membrane transport systems, cells or clumps of cells suspended in liquid to US.
85
What are the results of in vitro studies?
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
What bioeffects have in vivo studies shown potential for? (6)
- Fetal weight reduction
- Postpartum mortality
- Fetal abnormalities
- Tissue lesions
- Hind limb paralysis
- Blood flow stasis (clots)
87
What positive bio effects have been reported during in vivo studies?
Wound repair enhancement and tumor regression
88
What intensities are considered safe for an unfocused probe?
Intensities below 100 mW/cm squared
89
What intensities are considered safe for a focused probe?
Intensities below 1000 mW/cm squared
90
What is the difference in threshold between focused and unfocused probes?
It is 10x greater for focused probes
91
What are the two main categories of bioeffects?
1. Thermal
| 2. Non-thermal (mechanical)
92
What is absorption?
The conversion of heat to sound
93
What is attenuation primarily due to?
Absorption 80%
94
When are there no adverse thermal effects?
When the temperature increase is less than two degrees Celsius
95
At what temperature do adverse effects start occurring?
Over 6 degrees but only if the exposure time is over 16 minuets
96
What do adverse effects of increased temperature depend on in order to occur?
Longer exposure time gives a higher chance of adverse effects at higher temps
97
What are the types of mechanical effects?
1. Radiation force
| 2. Cavitation
98
What is radiation force?
The force exerted by sound on the medium which can deform and disrupt structures
99
What can radiation force cause?
Flow in absorbing fluids resulting in shear forces
100
What are shear forces?
Compression forces that force one part of the body in one direction and another in the opposite direction
101
What is cavitation?
The production and behaviour of bubbles in a liquid medium
102
How can cavitation be divided?
Stable cavitation and transient cavitation
103
What is stable cavitation?
Simple oscillation of the bubbles that can result in the streaming of liquid resulting in shear stresses
104
What is transient cavitation?
When the bubble actually collapses producing shock waves
105
What can the shock waves from transient cavitation result in?
Localized extremely high temps and can even emit light in clear fluids
106
What happened in 1992 regarding US and bioeffects?
A standard was set so that realtime info relating to the potential for bioeffects is displayed on the monitor
107
What is ODS?
Output Display Standard - the quantities relating to bio effect potential that are displayed on the US monitor.
108
What quantities are displayed for ODS?
1. Thermal Index (TI)
| 2. Mechanical Index (MI)
109
What is thermal index?
The ratio of acoustical power produced by the transducer to the power required to raise the temp in tissue by 1 degree celcius
110
A TI value of 1 means what?
That under assumed tissue conditions, a TI of 1 could POSSIBLY raise the temp of the tissue by 1 Degree celsius
111
How is TI further divided?
TIS
TIB
TIC
112
What is the most common type of TI?
TIS
113
What is TIS used for?
Soft tissue
114
What is TIB used for?
Bone near the focus, used for OB scanning
115
What is TIC?
Bone near the surface (ex. Transcranial)
116
What is TI divided into TIS,TIB, and TIS?
To account for the different tissue types and their respective absorption rates
117
What does Mechanical Index represent?
The likelihood that the energy used will lead to cavitation
118
What is the MI proportional to?
The peak rarefactional pressure
119
If the rarefactional pressure doubles, what happens to the MI?
Its proportional so the MI will double as well.
120
What is the MI inversely proportional to?
The square root of the frequency
121
If the MI reduced to half what happend to the frequency?
It quadrupled
122
In what cases could the TI and MI be underestimated?
In the presence of a large fluid collection (but these situations usually allow for less power).
123
What is important to consider as TI rises?
The exposure time
124
What is max TI?
6
125
What is max MI?
1.9
126
What is the specific SPTA allowed for Cardiac, peripheral vasc, ophthalmic, fetal and other exams?
Cardiac = 430
Fetal and other = 94
Periph Vasc = 20
Ophthalmic = 17
127
What are the typical output intensities (SPTA) from US scanners?
```
B-Scan = 18.7
M-mode = 73
CW = 1140
Doppler = 234
```
128
How can the diff applications of US be divided?
Scanned and non-scanned
129
What are the non-scanned types? (3)
1. CW
2. Pulsed Doppler
3. M-mode `
130
What type of US application poses the highest risk of for thermal effects and why?
Non-scanned, due to the fact that they transmit repeatedly in a straight line
131
What US application poses the biggest risk for thermal effects?
CW
132
Why are contrast agents concerning?
Recent studies show that gas bodies present in circulation can produce non-thermal adverse effects even when intensities are below threshold
133
Regarding contrast, at what MI value is there little risk?
MI below 0.4
134
What are the adverse effects of contrast?
1. Induction of premature ventricular contractions
2. Microvascular leakage with petechiae
3. Glomerular capillary hemorrhage
4. Local cell killing
135
What are petechiae?
Tiny dots on the skin caused by bleeding
136
What is important for practitioners to be aware of when using contrast?
1. Use minimal agent dose
2. MI
3. Examination time
137
What is ALARA?
As Low As Reasonably Achievable
138
What does ALARA mean?
The principle of keeping US exposure minimal while optimizing diagnostic information
139
What activities should US not be used for under Health Canada guidelines?
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
What are the 4 different restricted acts that sonographers will be required to perform once Alberta is self regulated?
1. OBS scans
2. EV's
3. Contrast
4. IV's
141
Once self regulation is finalized what will Alberta sonographers fall under?
ACMDTT
