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DMSO Physics > Chapter 6 Q & A > Flashcards

Chapter 6 Q & A Flashcards

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1
Q

decibels

every 3 db change means that the intensity will

A

double

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2
Q

every 10 dB change means the intensity will

A

increase 10 times

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3
Q

a reduction in the intensity of a sound beam to one-half of its original value is____dB

A

-3dB

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4
Q

a reduction in the intensity of a sound beam to one-quarter of it original value is ________db

A

-6 dB

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5
Q

-10dB means that the intensity is reduced to _______of its orgiginal value

A

one tenth

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6
Q

dB is a mthmatical representation with a _______scale

A

logarithmic and relative

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7
Q

we need one intensity to calculate decibels?

T or F

A

False

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8
Q

a wave’s intensity is 2mW/cm^2.

There is a change of +9db.

What is the final intensity?

A

16 mW/cm^2

+9 = 3db and 3db and 3db

so it is 2x2x2 or 8 times greater

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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

beam intensity is increasing

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10
Q

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

A

positive

beam intensity is increasing

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11
Q

name three components of attentuation

A

absorption

reflection

scattering

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12
Q

as the path penght 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 or same as) attentuatoin in soft tissue

A

greater than

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14
Q

attentuation in bone is ________attenuation in sfot 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?

T or F

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

in soft tissue the attenuation coefficient in dB per centimeter is approx one half 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 freq decreases, depth of penetration _________

A

increases

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21
Q

as path lenght increases the half boundry 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/m^3) 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 medium has the higher acoustic impedance?

A

mediums A has the higher acoustic impedance

impedance = speed x density so if one increase so does the impedance

impedance, speed and density are all directly related

26
Q

impedance is important in _______at boundries

A

reflections

27
Q

which is better to use while examing a carotid artery, a 7.5 or 3.0 MHz transduce?

A

7.5 Mhz

carotid is superficial and therefore does not need the deeper penetration of the lower freq

28
Q

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

What is the intensity reflection coefficient?

A

100%

the whole wave was reflected

29
Q

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

What is the reflected intensity?

A

50 w/cm^2

wave totally reflected

30
Q

a pulse of ultrasound is propagating in soft tissue such as the liver. The pulse strikes a boundry with a different soft tissue at normal incidence.

What portion of the intensity is reflected back toward the transducer and why?

A

very small percentage of sound is reflected at a boundry of two soft tissues. IMpedances are so similar

31
Q

Sound is traveling in a medium and strikes a boundry 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 must account for 100% of initial intensity

32
Q

a pulse of ultrasound is propagating in bone and strikes an interface with soft tissue at 90°. A giant reflection is caused

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

what can be said about the impedance of soft tissue

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

A

nothing can be stated about the impedance based on the information given

however, because a large refelction was creasted the impedances of these two media must be different.

Reflections with normal incidence are created based upon the difference in impedance, not actual values

33
Q

sound strikes a boundry 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 impedance of the two media are different. tow different media can have the same impedances

34
Q

which of the following terms does not belong with the others

orthogonally

oblique

normal

perpendicular

A

oblique

means other than 90°

the rest all mean = to 90°

35
Q

sound is traveling from bone to soft tissue.

The impedances of the media differ significantl;y and 90% of the beams intensity is relfected.

What percentage of the intensity is tranmitted?

A

10% transmission

conservation of energy 100% must be accounted for

36
Q

sound 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 intensity is transmitted?

A

99%

best choice since nearly all would be transmitted since the impedances are so close

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

little to no refraction occurs.

transmitted beam is refracted when the incidence is oblique and the propagatoins speeds are different. because soft tissue on either side of boundry are soft tissues, their speeds are nearly identical and little or no refraction ocurs

38
Q

a sound pulse travels in Medium 1 and strikes an interface wtih another tissue, medium 2 at 30°. The angle of transmission is 10°. From these facts alone what can be said about

speed of sound in Medium 1

speed of sound in Medium 2

difference between the speeds of media 1 and 2

A

we can say nothing about the speed of sound in media 1 and 2.

however since there is a difference in the angle of transmission the speeds are different in the media

refractoin depends on the difference of speed, not the actual speed

39
Q

sound pulse travfels in medium 1 and strikes an interface with medium 2 at 30°. the angle of transmission is 10°. In which medium dows the sound travel slowest

A

slowest in medium 2

when the angle of transmission is less that the angle of incidence the sound is slower in the 2nd medium

40
Q

sound pulse travels in medium 1 and strikes an interface wtih another tissue medium 2 at a 30°. The angle of transmission is 10°.

In which medium is the impedance higher?

A

refraction of sound at a boundry is unrelated to the impedance of the media therefore with the info given it cannot be determined

refractoin is only affected by the speed of the sound in the media

41
Q

sound travels in a medium and orthogonally strikes a boundry 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 refractoin cannot occur

refraction occurs only when there are different speeds and oblique incidence

both conditions must be met

42
Q

a sound wave strikes a boundry with normal incidence. The impedances of the two media are identical.

What percentage of the sound wave is refracted?

A

refractoin cannot occur with normal incidence

43
Q

the impedance of medium 1 is 8 rayls. The propagation speed is 1450m/s. The impedance of medium 2 is 6 rayls and the speed is 1855m/s. A sound beam strikes the boundry between the media and is both partially transmitted and reflected. The angle of incident beam is 30°.

What is the reflectoin angle

A

30° the angle of reflection alwasy equals the angle of incidence

44
Q

What does the 100mW/cm^2 represent

A

incident intensity of the sound beam

45
Q

what does the 3.5 dB/cm represent

A

attenuation coefficient of the sound in the media

46
Q

if the media are sfot tissue, what is an estimate of the ultrasound frequencey?

A

about 7 MHz

attenuation coefficient multiplied by 2 approximates the frequency

3.5x2=7

47
Q

what property hsa units of rayls?

how is it determined?

A

impedance

calculated not measured

impdedance= density x speed

48
Q

the incidence betweenthe sound wave and the boundry between media 1 and 2 is normal.

What happens at the boundry between 1 and 2?

Why?

A

both reflection and transmission occur

there are normal incidence and different acoustic impedances

49
Q

the incidence between the sound wave and the boundry between media 2 and 3 is normal.

What happens at the boundry between media 2 and 3?

Why?

A

transmission only

impedances of the media are the same

50
Q

what type of incidence is there between media 3 and 4?

A

oblique

51
Q

what happens at the boundry between media 3 and 4?

Why

A

reflection may occur

if transmission does occur the sound beam will refract because there are different propagatoins speeds and oblique incidence

52
Q

what processes occur as the ultrasound passes all media?

what are the units of this process?

A

attenuation occurs

dB

decibels

DMSO Physics (16 decks)

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