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Fall:Physics > book study questions Test2 > Flashcards

book study questions Test2 Flashcards

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1
Q

every 3dB change means that the intensity will:

A

double

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2
Q

every 10dB change means that the intensity will:

A

increase 10 times

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3
Q

a reduction in the intensity of a sound beam to 1/2 of its original value is:

A

-3dB

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4
Q

a reduction in the intensity of a sound beam to 1/4 of its original value is:

A

-6dB

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5
Q

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

A

1/10

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6
Q

dB is a mathematical representation with a _____ scale

a. logarithmic and relative
b. division and relative
c. longitudinal and relative
d. logarithmic and absolute

A

a. logarithmic and relative

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7
Q

we need one intensity to calculate decibels

A

false

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8
Q

a wave’s intensity is 2mW/cm2

there is a change of +9dB

what is the final intensity?

a. 6mW/cm3, b. 2mW/cm2, c. 16mW/cm2, d. 16µW/cm2

A

c. 16mW/cm2

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9
Q

if the final intensity of a sound beam is more than the initial intensity, then the gain in dB is:(+or-)

A

positive-the beam’s intensity is increasing

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10
Q

if the initial intensity of a sound beam is less than the final intensity, then the gain in dB is:(+or-)

A

positive-the beam’s intensity is increasing

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11
Q

name the 3 components of attenuation

A

absorption

reflection

scattering

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12
Q

as the path length increases, the attenuation of ultrasound in soft tissue:

A

increases

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13
Q

attenuation in lung tissue is (less than, greater than, the same as) attenuation in soft tissue

A

greater than

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14
Q

attenuation in bone is ____ attenuation in soft tissue

A

greater than

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15
Q

attenuation in air is ____ attenuation in soft tissue

A

greater than

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16
Q

what are the units of attenuation?

A

decibels (dB)

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17
Q

in a given medium, attenuation is unrelated to the speed of sound

A

true-attenuation and propagation speed are unrelated

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18
Q

what is the relationship between ultrasound frequency and the attenuation coefficient in soft tissue

A

attenuation coefficient in dB per centimeter is approx 1/2 of the ultrasonic frequency in MHz

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19
Q

what are the units of the half-value layer thickness?

A

distance-centimeters

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20
Q

as frequency decreases, depth of penetration:

A

increases

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21
Q

as path length increases, the half boundary layer:

A

remains the same

22
Q

impedance is associated with:

A

only the medium

23
Q

as the path length increases, the attenuation coefficient of ultrasound in soft tissue (decreases, remains the same, increases)

A

remains the same

24
Q

acoustic impedance=

_____x_____

A

density(kg/m3) x propagation speed(m/s)

25
Q

two media A and B have the same densities

the speed of sound in medium A is 10% higher than in medium B

which has the higher acoustic impedance?

A

medium A’s acoustic impedance is higher than medium B’s

recall that impedance = speed x density

since both media have identical densities and medium A’s speed is 10% higher, then medium A’s impedance is 10% higher

26
Q

impedance is important in ____ at boundaries

A

reflections

27
Q

which is better to use while examining a carotid artery, a 7.5 or 3.0MHz transducer?

A

7.5MHz transducer

higher frequency produces better image in a superficial structure

28
Q

a sound wave with an intensity of 50W/cm2 strikes a boundary and is totally reflected

what is the intensity reflection coefficient?

a. 50w/cm2, b. 25w/cm2, c. 0w/cm2, d. 100%, e. 0

A

d. 100%

coefficient is a percentage

29
Q

a sound wave with an intensity of 50W/cm2 strikes a boundary and is totally reflected

what is the reflected intensity?

a. 50w/cm2, b. 25w/cm2, c. 0w/cm2, d. 100%, e. 0

A

a. 50w/cm2

30
Q

a pulse of ultrasound is propagating in soft tissue, such as liver

the pulse strikes a boundary with a different soft tissue at normal incidence

what portion of the intensity is reflected back toward the transducer?

why?

A

a very small percentage of sound is reflected at a boundary between two soft tissues, because the impedances of the two soft tissues are similar

the difference in impedance directly determines the intensity reflection coefficient

31
Q

sound is traveling in a medium and strikes a boundary with normal incidence

If 63% of the wave’s intensity is reflected back toward the transducer, what percentage is transmitted?

A

37%

conservation of energy occurs at a boundary

everything must equal 100%

32
Q

a pulse of ultrasound is propagating in bone and strikes an interface with soft tissue at 90°

a giant reflection is created

from these facts alone, what can be said about the impedance of bone?

soft tissue?

what can be said about the differences between the impedances of bone and soft tissue?

A

nothing can be said about the impedance of bone or soft tissue based on the info given

because a large reflection was created, the impedances must be different

reflections with normal incidence are created based on the difference in the impedances, not on the actual values of the impedances

33
Q

sound strikes a boundary between two media orthogonally

although the media are very different, no reflection is created

how can this be?

A

with normal incidence, reflections occur only when the impedances of the two media at the interface are different

if the two media have the same impedances, no reflection occurs

34
Q

which of the following does not belong:

a. orthogonal, b. oblique, c. normal, d. perpendicular

A

b. oblique

all the others mean equal to 90°

35
Q

sound is traveling from bone to soft tissue

the impedances of the media differ significantly, and 90% of the beam’s intensity is reflected

what percentage of the intensity is transmitted?

A

10% is transmitted

36
Q

sound that is traveling in Jell-O passes through an interface at 90° and continues to travel in whipped cream

the impedance of Jell-o and whipped cream are nearly identical

what percentage of the intensity is transmitted?

a. 2%, b. 25%, c. 78%, d. 99%

A

d. 99%

best choice because the impedances are nearly identical

only a small percentage would reflect

37
Q

a pulse of ultrasound propagates in soft tissue, such as liver

the pulse strikes a soft tissue-soft tissue interface with oblique incidence

some of the sound energy is transmitted

to what extent is the transmitted beam refracted?

A

transmitted beam undergoes little to no refraction

transmitted beam is refracted when the incidence is oblique and the propagation speeds are different

38
Q

a sound pulse travels in medium 1 and strikes an interface with another tissue, medium 2, at 30°

the angle of transmission is 10°

from these facts alone, what can be said about:

the speed of sound in medium 1

the speed of sound in medium 2

the difference between the speeds of media 1 and 2

A

given only this info, nothing can be said about the speed of sound in medium 1 or 2

because the beam refracted significantly, the speeds of both media are different

39
Q

a sound pulse travels in medium 1 and strikes an interface with another tissue, medium 2, at 30°

the angle of transmission is 10°

in which medium does sound travel slowest?

A

sound travels slowest in medium 2

sound travels slower in the second medium when the angle of transmission is less than the angle of incidence

40
Q

a sound pulse travels in medium 1 and strikes an interface with another tissue, medium 2, at 30°

the angle of transmission is 10°

in which medium is the impedance higher?

A

with the info provided, it cannot be determined which material has the greater impedance

41
Q

sound travels in a medium and orthogonally strikes a boundary with a different medium

although sound waves traveling in the media have vastly different speeds, there is no refraction

how can this be?

A

with normal incidence, refraction cannot occur

refraction only occurs when there are different speeds and oblique incident

42
Q

a sound wave strikes a boundary with normal incidence

the impedances of the two media are identical

what percentage of the sound wave is refracted?

a. 100%, b. 75%, c. 0%, d. 25%, e. 90%

A

c. 0%

refraction cannot occur with normal incidence

43
Q

the impedance of medium 1 is 8 rayls

the propagation speed is 1,450 m/s

the impedance of medium 2 is 6 rayls and the speed is 1,855 km/s

a sound beam strikes the boundary between the media and is both partially transmitted and reflected

the angle of the incident beam is 30°

what is the reflection angle?

A

30°

the angle of reflection = the angle of incidence

44
Q

a sound wave is created by a transducer, reflects off an object, and returns to the transducer

the depth of the reflector is 10cm in soft tissue

what is the go-return time?

a. 13µs, b. 1.3µs, c. 65µs, d. 130µs

A

d. time of flight = depth x 13µs

10cm x 13µs/cm = 130µs

45
Q

a sound wave is created by a transducer, reflects off an object, and returns to the transducer

the go-return time is 26µs

what is the depth of the reflector?

a. 1cm, b. 2cm, c. 3cm, d. 4cm

A

b. the reflector depth is 2cm

2cm x 13µs/cm = 26µs

46
Q

a sound wave is created by a transducer, reflects off an object, and returns to the transducer

the go-return time is 26µs

what is the total distance that the pulse traveled?

a. 1cm, b. 2cm, c. 3cm, d. 4cm

A

d. total distance traveled is twice the depth of the reflector

47
Q

the maximum imaging depth (depth of view) during an ultrasound exam is 10cm

the sonographer adjusts the imaging depth to 20cm

what happens to pulse repetition period?

A

pulse repetition period is DIRECTLY related to imaging depth

when imaging depth doubles, pulse repetition period doubles

48
Q

the maximum imaging depth during an ultrasound exam is 10cm

the sonographer adjusts the imaging depth to 20cm

what happens to pulse repetition frequency?

A

pulse repetition frequency is INVERSELY related to imaging depth

when imaging depth doubles, PRF is halved

49
Q

the imaging depth during an ultrasound exam is 10cm

the sonographer adjusts the imaging depth to 5cm

what happens to pulse repetition period?

A

pulse repetition period is DIRECTLY related to imaging depth

when the imaging depth is halved, PRP is halved

50
Q

a sound wave is created by a transducer, reflects off an object, and returns to the transducer

the imaging depth is 10cm in soft tissue

what is the maximum pulse repetition frequency?

a. 7,700, b. 7.7kHz, c. 3,500 Pa, d. 7,700µs

A

b. only one with correct units

51
Q

a sound wave is created by a transducer, reflects off an object, and returns to the transducer

the maximum imaging depth is 7.7cm

what is PRF?

a. 7,700Hz, b. 5,000kHz, c. 10,000Hz, d. 100µs

A

c. 77,000/7.7 = 10,000Hz

52
Q

a sound wave is created by a tranducer, reflects off an object, and returns to the transducer

the go-return time is 130µs

what is the maximum PRF?

a. 7,700Hz, b. 5,000kHz, c. 10cm, d. 100µs

A

a. 7,700Hz

Fall:Physics (10 decks)

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