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Ultrasound Physics > Ch 5, 6, 7 > Flashcards

Ch 5, 6, 7 Flashcards

1
Q

How long does it take for sound to make a round trip to and from the skin’s surface to a reflector depth of 1 cm in soft tissue?

A

13 us

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2
Q

In soft tissue, sound travels to a reflector and back to the transducer in 39 us. How deep is the reflector?

A

39/13 = 3cm

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3
Q

In soft tissue, sound travels to a reflector and back to the Tx in 39us. What is the total distance that the pulse traveled?

A

39/13= 3cm (x2) = 6cm

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4
Q

One reflector is 5 times deeper than another. The time of flight of sound to the deeper structure is _____ the time of flight of the shallower reflector.

A

5 times greater than

Time of flight is directly related to depth of reflector.

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5
Q

True or False?

We need one intensity to calculate decibels?

A

False- decibels measure relative changes, comparison/ratio

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6
Q

-10dB means that the intensity is reduced to ____ of its original value.

A

One-tenth

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7
Q

What is the log is 10,000?

A

4

10x10x10x10

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8
Q

Every 3 dB means that the intensity will ____.

A

Double

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9
Q

A drop in intensity to one-quarter of its original value is ___dB.

A

-6

If -3dB is half, then -6 dB is one quarter

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10
Q

A wave’s intensity is 2mW/cm^2. There is a change +9 dB. What is the final intensity?

A

Bc it’s +9dB -every 3 decibels doubles so it would be

2(2)=4(2)=8(2)= 16

break it down

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11
Q

What combination of the following is related to greater attenuation?

Long or short distance

AND

Low or high frequency

A

Long distance

High frequency

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12
Q

What combination of the following results in the wave with the highest intensity?

Long or short distance

AND

Low or high frequency

A

Short Distance

Low frequency

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13
Q

Which of the following results in the least attenuation?

A) 4MHz sound, path length 2 cm
B) 4 MHz sound, path length 8 cm
C) 6 MHz sound, path length 8 cm
D) 6 MHz sound, path length 4 cm

A

4 MHz sound, path length 2 cm

High frequency, short distance

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14
Q

Which of the components of attenuation is the dominant contributor?

A

Absorption

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15
Q

Rayleigh scattering is proportional to _____.

A

Frequency^4

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16
Q

Attenuation is measured in ___.

A

Decibels

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17
Q

____ is an extremely low attenuater.

A

Water

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18
Q

____ has the highest attenuation.

A

Air

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19
Q

Bone and lungs have a _____ attenuation.

A

High

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20
Q

What is the relationship btw propagation speed and attenuation coefficient in soft tissue?

A

They are unrelated

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21
Q

In soft tissue, attenuation coefficient is directly related to ____.

A

Frequency

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22
Q

As path length increases, the attenuation coefficient of ultrasound in soft tissue _____.

A

Remains the same

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23
Q

A sound wave, with an intensity of 50W/cm^2, strikes a boundary and is totally reflected.

What is the IRC?

A

100%

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24
Q

A sound wave, with an intensity of 50W/cm^2, strikes a boundary and is totally reflected.

What is the reflected intensity?

A

50W/cm^2

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25
The ITC of sound is 99.9%. What percent of sound is reflected back to the transducer?
0.1%
26
What is this formula for? (Z2-Z1 / Z2+Z1) x100
IRC%
27
ITC% =
(Transmitted intensity/ incident intensity) x 100 Or ITC%= 1-IRC
28
What is Snell’s Law?
Quantifies the physics of refraction Sin(transmission angle)/sin(incident angle) = speed of med 2/ speed of med 1
29
The angle btw an ultrasound pulse and the boundary btw two media is 56 degrees. This is called _____.
Oblique incidence
30
With normal incidence, what factors affect refraction?
None
31
True or false? Right angle incidence reflections are always generated at a boundary if the propagation speeds of the media are different.
False
32
What is most likely to create Rayleigh scattering?
Red blood cells
33
Snell’s law describes physics of ____.
Refraction
34
The most likely amount of reflection at a boundary btw soft tissue is ____.
1%
35
Sound is traveling from medium 1 to medium 2. Propagation speeds of M1 and M2 1600 m/s and 1500 m/s respectively. There is normal incidence. A) incident angle > reflection angle B) incident angle = reflection angle C) incident angle < reflection angle
Incident angle = reflection angle
36
Intensities may be reported in various ways with respect to ___
Time and space
37
____ measurements are important in the study of ____
Intensity | Bioeffects
38
What is the measurement for all intensities?
W/cm2
39
____ is the most relevant intensity with respect to tissue heating
SPTA | Spatial peak temporal average
40
Bc peak measurements are larger than avg measurements, ____ intensity has the highest value while ____ has the lowest value.
SPTP (spatial peak temporal peak) | SATA (spatial avg temporal avg)
41
____ is always higher than Spatial avg intensity.
Spatial peak intensity
42
A number called _____ describes the spread of a beam in space.
Beam uniformity coefficient - also called SP/SA factor SP/SA factor is unitless with a value of 1 or greater
43
____ describes the relationship of the beam intensities with time. A unitless number with a value btw 0 & 1
Duty factor
44
For a ____ ultrasound, the beam is always “on” and the pulse avg and temporal avg intensities are the same. Thus, ___ = ____ and ___=____
Continuous wave SPTA=SPPA SATA=SAPA
45
When pulsed and continuous wave sound beams have the same ____ intensities, the continuous wave beam has the higher SPTA intensity.
SPTP
46
When pulsed and continuous wave sound beams have the same SATP intensities, the continuous wave beam has the higher _____ intensity.
SATA
47
Itp is the maximum intensity in ____
Time
48
Im intensity is averaged over the most intense ___
Half-cycle
49
Ipa is averaged only during the pulse duration ____ time only.
“On”
50
Ita is averaged during the ___
PRP both “on” and “off” times
51
Rank intensity from largest to smallest
``` SPTP Im SPPA SPTA SATA ```
52
Isp is the maximum in ____
Space
53
Isa is averaged over the _____ of the beam
Cross sectional area
54
Attenuation is measured in ____ and reported as a ____ change.
Decibels | Relative
55
10 dB of attenuation means
A decrease in 10dB -10dB
56
___ is likely to occur when the dimension of a boundary is large
Reflection
57
2 types of reflection
Specular | Diffuse (backscatter)
58
Sound scatters when tissue _____
Interface is small
59
Scattering is directly related to ____
Frequency
60
Lung tissue ____ bc aveoli are filled with air.
Scatters
61
One example of Rayleigh scattering is when there is interaction of ultrasound and ____
RBC
62
____ is the largest component of attenuation
Absorption- when ultrasound energy is converted to another energy (heat)
63
Due to ____, high frequency waves attenuate more than lower frequency waves.
Absorption
64
A tissue’s impedance is ____ not ____.
Calculated not measured for
65
Sound not reflected must be ____.
Transmitted
66
With normal incidence, what factors affect refraction?
None
67
Incidence angle ALWAYS equals ____
Reflection angle
68
2 physical principles ALWAYS apply to reflection with oblique incidence:
Conservation of energy | Reflection angle = incident angle
69
Refraction ONLY occurs with ___ and ____
Oblique incidence and different propagation speeds
70
Whichever medium has the higher speed has the ____ angle.
Greatest
71
Time of flight is ____ for shallow and ___ for deep reflectors.
Shorter | Longer
72
Time of flight (go return time/round trip time) is directly related to
Depth of reflector
73
Time of flight is calculated using
Speed of sound in soft tissue (1.54mm/us) and go return time
74
A pulse’s time of flight will be twice as long for a reflector that is ____ the depth of another.
Twice
75
13 microsecond always applies when
Sound travels through soft tissue
76
Total distance is always ___ the depth.
Twice
77
____ is the go return time of a sound pulse btw the transducer and the bottom of the image.
PRP
78
PRP =
imaging depth (cm) x 13 us/cm
79
If the imaging depth is 10 cm, what is the PRP?
Depth x 13 us/cm 10x13 = 130 us
80
If there is a depth of 5 cm, what is the PRP?
5cm x 13us/cm = 65us
81
In one second, sound can travel into tissue AND return from a depth of ____.
77,000 cm (nearly half a mile)
82
In 1 one second, sound can travel to and from 77 cm a total of ___ times
1,000
83
In 1 one second, sound can travel to and from 7.7 cm a total of ___ times
10,000
84
Shallow depth of view = ___ PRF
High (more cycles per second)
85
Deep depth of view =
Low PRF (less cycles per second)
86
PRF (Hz) =
77,000 cm/s / imaging depth(cm)
87
If the depth is 7.7 cm, what is the PRF?
77,000 / 7.7 = 10,000 Hz *remember PRF is measured in Hz

Ultrasound Physics (6 decks)

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