Quiz 2 Flashcards
(108 cards)
1
Q
The time from the start of one pulse to the start of the next is called
A
PRP
2
Q
The on time of the pulse is referred to as
A
Pulse duration
3
Q
Pulse duration is directly related to the number of cycles. True or False?
A
True
4
Q
SPL is determined by
A
source and medium
5
Q
PRP is the sum of
A
pulse duration plus listening time
6
Q
What determines PRF
A
Medium and source
7
Q
If we increase depth on the image, the PRF will
A
decrease
8
Q
The duty factor of Continuous wave (CW) ultrasound is
A
100% or 1
9
Q
The sonographer can change all of the following EXCEPT
A
PD
SPL
10
Q
What does a 10dB change in intensity signify?
A
The intensity has increased 10 times larger
11
Q
If a sound beam has increased from its original intensity by a factor of 1000, how would this show in decibels?
A
30 dB
12
Q
What happens to sound as it travels to a deep internal organ?
A
increased attenuation
13
Q
Which of the following does NOT cause attenuation?
A
Lower frequency
14
Q
What are the three primary causes of attenuation?
A
- Reflection
- Scattering
- Absorption
15
Q
What is the relationship between water and bone in terms of attenuation?
A
Water has a lower attenuation than bone
16
Q
Tissues that are very attenuating have what type of half value layer?
A
Thin
17
Q
What does Snell’s Law describe?
A
Snell’s Law tells us how the angles of incidence and refraction of a wave are constant when it passes through 2 mediums (tissues).
18
Q
In order to have reflection at normal incidence, the impedance must be _______.
A
Different
19
Q
What are the units of pulsed duration?
A
Microseconds
20
Q
What determines pulsed duration?
A
Source of sound
21
Q
Can pulsed duration be changed?
A
No
22
Q
What is the formula for pulse duration?
A
P=1/f Or F=1/p
23
Q
What is SPL
A
the length of the pulse from the start to the end
24
Q
What are the units for SPL?
A
mm
25
How can SPL be determined?
By source and medium
26
Can SPL be changed?
No
27
What is the relationship between SPL and wavelength?
Directly related to
28
What is the relationship between SPL and PRF?
Inversely related
29
What is the relationship between SPL and the # of cycles?
Directly related
30
What is the formula for SPL?
SPL(mm) = # of cycles times wavelength (mm)
31
What is PRP?
The time from the beginning of a pulse to the beginning of the next pulse. It is the on and off time combined.
32
What are the units of PRP?
ms
33
How is PRP determined?
By source
34
Can PRP be changed?
Yes, by changing the depth
35
True or false. If a tissue is deep, PRP would be longer because the system has to wait for it to get back to the transducer.
True
36
What is PRF?
The number of pulses transmitted into the body each second
37
What are the units for PRF?
Hz
38
How is PRF determined?
By the source
39
Can PRF be changed?
Yes by changing the depth
40
How is PRP and PRF related?
Inversely
41
What is the formula for PRF?
PRF = 1 divided by PRP
42
What is duty factor?
The percent of time that the pulse is being transmitted
43
What is the unit for duty factor?
There is no unit!
44
How is duty factor determined?
By sound source
45
Can duty factor be changed?
Yes (if depth changes then duty factor changes)
46
What is the formula for duty factor?
Duty factor% = PD divided by PRP times 100
47
What is the minimum value of duty factor?
0%
48
What are the 3 things that can be changed by the sonographer?
PRP
PRF
PD
49
What are the 2 things that can not be changed by the sonographer?
PD
SPL
50
How does sound interact with tissues?
The sound wave will hit boundaries between tissues to create weak reflections.
51
What is attenuation?
Sound waves weaken as they move through tissue
52
What does a positive decibel mean?
Strength is increasing
53
What does a negative decibel mean?
Strength is decreasing
54
Is a decibel relative or absolute?
Relative
55
True or false. Decibels are a ratio.
True
56
Are decibels logarithmic?
Yes - allows for large ranges of sound intensity to be in manageable units
57
What does +3dB mean?
Double
58
What does +10dB mean?
Ten times larger
59
What does -3dB mean?
Half
60
What does -10dB mean?
One-tenth of
61
Attenuation is a decrease in?
Intensity
Power
Amplitude
62
Attenuation is determined by?
Distance
Frequency of sound
63
What is reflection?
As sound hits a boundary part of the energy will be reflected back to the transducer.
This weakens the part of the wave the continuous to move forward.
When dimension of a boundary is LARGE a reflection can occur
64
What are the 2 types of reflections?
Specular and Diffuse
65
What are specular reflections?
Smooth boundary
One direction
Organized
66
What is another name for diffuse reflections?
Backscatter
67
What are diffuse reflections?
Irregular boundary
More than one direction
68
What is the advantage of backscatter (diffuse)?
Suboptimal angles can still produce reflections
69
What is the disadvantage of backscatter (diffuse)?
Lower strength than specular reflections
70
What is scattering?
Small tissue interference that is equal to or less than the wavelength of the incident sound wave
Random redirection of sound in several directions
71
How is scattering related to frequency?
Directly related to
72
What is Rayleigh scattering?
Scattering that happens when the structure is smaller than the beam wavelength
Equally redirected in all directions
73
If frequency doubles, what happens to scattering in regards to Rayleigh scattering?
It increases by 16 times
74
What is absorption?
When energy is converted to heat
Higher the frequency, higher the amount of absorption
75
What is the biggest cause of attenuation?
Absorption
76
How is absorption related to frequency?
Directly related to
77
What does total attenuation depend on?
Frequency
Distance
Tissue
78
True or false. High frequencies attenuate more?
True
79
What are the units for attenuation coefficient?
dB/cm
80
What is the formula for calculating attenuation coefficient in soft tissue and what is the transducers frequency?
AC(dB/cm) = frequency (MHz) divided by 2
1/2 the transducers frequency
(.5)
81
How is attenuation coefficient related to frequency?
Directly related to
82
What does attenuation coefficient tell us?
For each cm that sound travels, more energy is lost
83
What is the formula for total attenuation?
Total Att. (dB) = Att. Coefficient (dB/cm) times path length (cm)
84
How much sound is attenuated in water?
Extremely low amounts of
85
How much sound is attenuated in blood, urine, fluids?
Low amounts
86
How much sound is attenuated in fat?
Low amounts
87
How much sound is attenuated in soft tissue?
Intermediate amounts
88
How much sound is attenuated in muscle?
High amounts of
89
How much sound is attenuated in bone and lung?
Higher amounts than muscle
90
How much sound is attenuated in air?
Extremely high amounts of
91
What is the units for half value layer?
cm
92
What is half value layer dependent on?
Medium and
Frequency
93
Tissues that have low attenuation have what type of half value layer?
Thick
94
Why is transmission important?
Allows for imaging deeper tissues
95
What is impedance?
The tissues resistance to the ultrasound as it travels through tissue
96
What is acoustic impedance?
The calculated amount of resistance a medium has on a sound wave
Density X speed of sound
97
What is the formula for acoustic impedance?
Density (kg/m3) X propagation speed(m/s)
98
What is the unit for impedance?
Rayls (Z)
99
What is impedance determined by?
Medium
100
What is normal incidence?
Wave hits interface at 90 degrees
101
What is oblique incidence?
Wave hit boundary at any other angle than 90 degrees
(Ex. 60 degrees , 20 degrees)
102
What are the 3 type of intensities?
Incident
Reflected
Transmitted
103
What is incident intensity?
Sound intensity before it hits interface
104
What it reflected intensity?
Sound intensity after hitting interface and returns back to source
105
What is transmitted intensity?
Sound intensity after sticking a boundary and then comes forward in the direction it was propagating
106
What is Snells law?
The greater the difference between the impedance of 2 materials, the greater the proportion of sound is reflected
107
What is refraction?
The bending of a sound wave as it strikes the interface
108
What does refraction require?
Oblique incidence
A difference in speed of sound in two mediums
