Quiz #2 Flashcards
(121 cards)
1
Q
What is attenuation?
A
It is a loss of energy.
2
Q
What happens when sound waves travel through a tissue?
A
It weakens.
3
Q
What does a wave lose the deeper it propagates?
A
A wave loses amplitude, power and intensity (energy.)
4
Q
What does attenuation depend on?
A
It depends on frequency, distance and tissue.
5
Q
What is the relationship between frequency, distance and attenuation?
A
They are directly related.
6
Q
What is attenuation always measured in?
A
dB
7
Q
What are the 3 sources of attenuation?
A
- Reflection
- Scattering
- Absorption
8
Q
What is the most important source of attenuation?
A
Absorption, which is in the form of heat.
9
Q
Will you have more or less attenuation with longer distances?
A
More attenuation.
10
Q
Will you have more or less attenuation with shorter distances?
A
Less attenuation.
11
Q
Will you have more or less attenuation with higher frequencies?
A
More attenuation.
12
Q
Will you have more or less attenuation with lower frequencies?
A
Less attenuation.
13
Q
Echo amplitude lost by:
A
dB/cm
14
Q
For most soft tissues, the attenuation coefficient is?
A
.5-1 dB/cm for a 1 MHz probe.
15
Q
What is the attenuation coefficient for water?
A
.0002
16
Q
What is the attenuation coefficient for blood?
A
0.18
17
Q
What is the attenuation coefficient for the liver?
A
0.5
18
Q
What is the attenuation coefficient for the muscle?
A
1.2
19
Q
What is attenuation highly dependent on?
A
It is highly dependent on probe frequency.
20
Q
What happens to attenuation coefficient for a tissue at 1MHz when using a 2MHz probe?
A
It doubles.
21
Q
What happens to attenuation coefficient for a tissue at 1 MHZ when using a 4MHz probe?
A
It quadruples.
22
Q
How do you calculate attenuation?
A
dB=(Tissue attenuation coefficient)x(distance)x(frequency of probe)
23
Q
What is the term used to describe the brighter echoes deep to a liquid mass compared to adjacent tissues?
A
Enhancement.
24
Q
What is penetration?
A
depth.
25
What improves penetration?
Penetration improves with a lower frequency probe (less attenuation).
26
What is resolution?
Clarity.
27
What improves the resolution?
Resolution improves with a high frequency probe (decreased wavelength).
28
What is another way to describe attenuation?
Half value attenuation.
29
What does half value thickness equal?
It equals the distance sound must travel to reduce the intensity to 1/2 its original value.
30
Describe THIN HALF VALUE
It can't go very deep without losing half its energy.
31
What are the characterisitics of THIN HALF VALUE?
- High attenuation
- High frequency
- Tissue with high impedance
32
Describe THICK HALF VALUE
It can go very deep before losing half its energy.
33
What are the characteristics of THICK HALF VALUE?
- Lower attenuation
- Low frequency
- Tissue with low impedance.
34
What is the most important cause of attenuation?
Absorption.
35
```
Which of the following transducers would be the best choice for scanning the greater saphenous vein?
A. 2 MHz
B. 5 MHz
C. 7 MHz
D. 10 MHz
```
D. 10 MHz
36
```
Which of the following transducers would be the best choice for scanning the renal arteries?
A. 2 MHz
B. 5 MHz
C. 7 MHz
D. 10 MHz
```
A. 2 MHz
37
What is the term used to describe the brighter echoes deep to a liquid mass compared to adjacent tissues?
Enhancement
38
Why are the echoes deep to a fluid filled structure brighter?
The fluid has less attenuation than adjacent tissues.
39
How does the sound beams interact with the tissues?
- Some energy is reflected (as echoes)
- Some energy is transmitted (travels deeper)
- Some energy is changed (absorbed as heat)
40
What are B-mode images created from?
B-mode images are created from echoes while some energy is transmitted deeper.
41
What does it mean when energy remains constant?
It is not lost, only changed (conservation of energy)
42
How is ultrasound energy changed?
It is reflected, transmitted or changed into heat.
43
What are the 3 main reflectors?
1. Specular; which can be prependicular or non perpendicular
2. Diffuse or non-specular
3. Scatterer; Rayleigh scatter.
44
What are specular reflectors?
It is the bouncing of light from the surface of a mirror, or something similarly shiny and smooth, where parallel rays of light all bounce off at the same angle.
45
What are the two types of specular reflectors?
- Perpendicular
| - Non-perpendicular
46
What is "incidence"?
It refers to the angle the soundbeam came in to hit the flat surface specular reflector.
47
Incidence and transmitted beams are at the same angle as long as what?
Tissue 1 and tissue 2 have similar speed of sound.
48
On an ultrasound b-mode image, how can you tell what is a perpendicular or non-perpendicular image?
- Perpendicular image: Detail is visible (double lines in the vessel wall)
- Non-perpendicular: double line is not visible
49
When scanning a specular reflector, a 90° angle of incidence yields what quality of picture?
It yields a clearer image.
50
How can a sonographer obtain a perpendicular image with their probe?
The heel and toe method.
51
At a specular reflector with perpendicular incidence, how much energy is reflected?
It depends on the difference of the tissues at the interface.
52
What does the amplitude or strength of the reflected wave (echo) depend on?
It depends on the difference in acoustic impedance of the tissues at interface.
53
The bigger the difference in acoustic impedance....
The greater the percentage of energy is reflected.
54
What is an interface?
- Boundary
- Border
- Crossing point
- Edge
55
What are some examples of interfaces encountered by the ultrasound beam?
- air to muscle
- muscle to blood
- blood to fat
- muscle to bone
56
What is the symbol for acoustic impedance?
Z
57
What is acoustic impedance?
It is a characteristic of the tissue that affects the amplitude of an echo.
58
What is the equation for acoustic impedance?
Z= ρ x C
ρ= density
c=speed of particle vibrations.
59
What is the unit for acoustic impedance?
Rayl.
60
What is the acoustic impedance for lungs?
.18
61
What is the acoustic impedance for fat?
1.34
62
What is the acoustic impedance for kidney?
1.63
63
What is the acoustic impedance for blood AND liver?
1.65
64
What is the acoustic impedance for muscle?
1.71
65
What is the acoustic impedance for skull bone?
7.8
66
What is the reflection coefficient?
It is the % of strength of wave that is reflected at an interface.
67
What does the reflection coefficient depend on?
It depends on Z and C (acoustic impedance and speed of particle vibration)
68
what are the two types of reflection coefficient?
- amplitude reflection coefficient
| - Intensity reflection coefficient
69
What is amplitude?
Strength and acoustic pressure.
70
What is AMPLITUDE REFLECTION COEFFICIENT? (aka ARC)
it is the percentage of the strength of the wave that is reflected at an interface.
ARC= P(reflected)/P(Incident)
P=amplitude or acoustic pressure.
71
What is the equation for ARC?
ARC%=Pr/Pi=(Z2-Z1)/(Z2+Z1)
*the answer should always be a percentage.
72
When does reflection occur?
It occurs when adjacent tissues have different acoustic impedances.
73
When do interfaces reflect more?
When there are large differences in their impedance.
74
For soft tissue interfaces, the reflection coefficient is?
Less than .1
75
air and bone offer large impedance mismatches to issue, which causes?
Very little ultrasound to transmit past these medias.
76
Why do we use gel between the transducer and the skin?
It has similar impedance to soft tissue.
77
What is a diffuse reflection?
Light bounces off all kinds of random angles due to the imperfections in the surface.
78
Most interfaces in the body are regular or irregular?
irregular.
79
Which reflection produces weaker echoes?
Diffuse reflection.
80
What is another name for diffuse reflection?
Backscatter.
81
What is the most important source of echoes in the body?
Acoustic scattering.
82
What are the size of scatters?
It is the size of the wavelength or smaller.
83
Where do scatters reflect beams?
In all directions, in a disorganized and chaotic fashion..
84
What are rayleigh scatters?
RBC
85
What is the rayleigh scatters reflector size in comparison to the wavelength?
It is MUCH less than the wavelength.
86
Since rayleigh scatters have very weak echoes, what happens to the screen?
The screen is black.
87
When does rayleigh scattering increase?
Rayleigh scattering increases greatly as frequency increases.
88
What is hyperechoic?
Areas of increased level of scattering compared to surrounding tissue. (brighter)
89
What is hypoechoic?
Areas of decreased level of scattering compared to surrounding tissue. (darker)
90
What does echogenic mean?
Echoes present.
91
What does echolucent mean?
No echoes.
92
What does homogenous mean?
Similar strength echoes.
93
What does heterogenous mean?
Bright and dark.
94
What is refraction?
Reffraction is when an ultrasound beam meets an interface of tissues with different propagation speeds at a non-perpendicular angle, refraction may occur.
95
Refraction can cause what?
It can cause an artifact whereby s dtructure may appear on the image in a different location than it is.
96
What does Snell's law predict?
It predicts the amount of refraction.
97
What must you have for an artifact to occur?
A non-perpendicular angle.
98
Slow to fast C yields what?
A higher angle of transmission.
99
Fast to slow C yields what?
A lower angle of transmission.
100
For refraction to occur there must be these two criteria:
- Sound beam must approach a specular reflector at a non-perpendicular angle.
- C must be different on each side of the specular reflector.
101
What is the equation for Snell's law?
SINt=(C2xSINi)/C1
102
What is the speed of sound for fat?
1460
103
What is the speed of sound for the liver?
1560
104
What is the speed of sound for soft tissue?
1540
105
What is the speed of sound for blood?
1560
106
What is the speed of sound for muscle?
1600
107
What is the speed of sound for bone?
4080
108
There is a critical incident angle whereby no energy travels past the interface, and all the energy is reflected. What is it called?
Total internal reflection.
109
The acoustic impedance is a characteristic of the _______
A. Tissue
B. Soundwave
C. Ultrasound Wave
D. Pressure
B. Tissue
110
The acoustic impedance is a calculation based on which two measurements?
A. Frequency and amplitude
B. Propagation speed and density
C. Attenuation coefficient and wavelength
D. Pressure and frequency
B. Propagation speed and density
111
```
Acoustic impedance affects which of the following?
A. Rarefraction
B. Reflection
C. Frequency
D. Period
```
B. Reflection
112
```
Acoustic impedance is measured in which of he following units?
A. Hz
B. Cm/sec
C. mmHg
D. Rayls
```
D. Rayls
113
What abbreviation is used for acoustic impedance?
Z
114
```
The amplitude reflection coefficient (ARC) of a boundary indicates the percentage amount of the sound that will be?
A. Reflected
B. Transmitted
C. Refracted
D. Attenuated
```
A. Reflected
115
If a sound wave hits a boundary with two very different acoustic impedance most of the soundwave energy will be_________
Reflected with little transmission, if any.
116
If a soundwave hits a boundary with two similar acoustic impedance's most of the soundwave energy will________
Be transmitted deeper into the tissue .
117
If an ultrasound beam leaves the transducer and hits air in its path along the way, what will happen to the image and why?
When the ultrasound beam hits air, most of the energy will be reflected due to the large mismatch in acoustic impedances of the air/tissue boundary. Since nearly 100% of the energy is reflected, basically no energy is transmitted to be reflected from the tissue below the air. Instead, there is a dark area which appears below the air which is called an acoustic “shadow”.
118
Which of the following conditions must be present for refraction to occur?
A. Perpendicular angle to a specular reflector.
B. Non-perpendicular angle to a tissue interface with similar impedances
C. Perpendicular angle to a diffuse reflector.
D. Angle less than 90° crossing tissues with different propagation speeds.
D. Angle less than 90° crosing tissues with differing propagation speeds.
119
Which type of reflector may result in refraction of the ultrasound beam?
A non-perpendicular beam on a specular reflector.
120
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Refraction is important because it may result in which of the following?
A. An accurate image
B. An artifact
C. Increased frequencies
D. Visualizations of blood flow
```
B. An artifact
121
Snell's law predicts _____ when refraction occurs.
The angle difference of a transmitted beam and an incident beam.
