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Vascular I & Physics I > Ch. 6 Physics > Flashcards

Ch. 6 Physics Flashcards

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1
Q

A measurement tool used to report attenuation changes, relative changes of sound beams and ratio

A

decibel notation

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2
Q

A mathematical construct or method of rating numbers

A

logarithm

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3
Q

Represents the number of 10s that are multiplied to create a number

A

log

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4
Q

The number of decibels of attenuation that occurs when sound travels one centimeter

A

attenuation coefficient

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5
Q

How sound weakens as it travels through the body

A

attenuation

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6
Q

Is there a relationship between attenuation and speed

A

no

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7
Q

Describe US signals decreasing in strength

A

negative decibels

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8
Q

Describe US signals increasing in strength

A

positive decibels

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9
Q

When sound strikes a boundary and a portion of the wave’s energy may be redirected back to the sound source

A

reflection

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10
Q

When sound waves reflect off an irregular boundary + radiate in more than one direction

A

diffuse reflection

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11
Q

When the US beam hits a smooth boundary and the sound is reflected in only one direction

A

specular reflection

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12
Q

Distance and attenuation are

A

directly related

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13
Q

Intensity and attenuation are

A

directly related

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14
Q

The number of decibels of attenuation that occurs when sound travels one cm

A

attenuation coefficient

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15
Q

When US energy is converted to another energy form (i.e. heat) and is the most sizeable component of attenuation

A

absorption

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16
Q

The distance sound travels in a tissue that reduces intensity by 1/2

A

half-value layer thickness

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17
Q

Random redirection of sound waves in many directions

A

scattering

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18
Q

When a sound beam is reflected equally in all directions

A

Rayleigh scattering

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19
Q

The process of sound energy being extracted from a wave by absorption, scattering and reflection

A

attenuation

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20
Q

Greater than 90 degrees

A

obtuse angle

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21
Q

The acoustic resistance to sound traveling in a medium

A

impedance

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22
Q

Exactly 90 degrees

A

right angle

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23
Q

Less than 90 degrees

A

acute angle

24
Q

Incident intensity=

A

reflected intensity + transmitted intensity

25
Q

The intensity of a sound beam that returns after striking a boundary

A

reflected intensity

26
Q

The intensity of a sound beam that continues forward after striking a boundary

A

transmitted intensity

27
Q

Sound wave intensity before it strikes a boundary

A

incident intensity

28
Q

When incident angle of sound beam strikes a boundary at any angle other than 90 degrees

A

oblique incidence

29
Q

IRC% + ITC%=

A

100%

30
Q

% of US intensity that bounces back when beam hits a boundary between 2 media

A

intensity reflection coefficient (IRC)

31
Q

Amount of ultrasound intensity reflected at a boundary in soft tissue

A

less than 1%

32
Q

% of US intensity that continues when beam strikes interface between 2 media

A

intensity transmission coefficient (ITC)

33
Q

Amount of ultrasound intensity transmitted at a boundary in soft tissue

A

> 99%

34
Q

US beam strikes a tissue boundary at a 90 degree angle is called

A

normal incidence

35
Q

If an ultrasound beam strikes a tissue boundary at any angle other than 90 degrees it is

A

oblique incidence

36
Q

When the transmission angle is greater or less than the incident angle what happens

A

refraction

37
Q

Quantification of the physics of refraction

A

snell’s law

38
Q

Occurs only if these two conditions are present - oblique incidence and different prop speeds. Causing “bending” of the sound beam

A

refraction

39
Q

With oblique incidence, the reflection angle equals

A

incident angle

40
Q

When media on either side of a boundary have different impedances and the sound beam is at a 90 degree angle to the tissue boundary

A

normal incidence

41
Q

Units for measuring impedance

A

rayls

42
Q

Units of intensities

A

w/cm squared & time and space

43
Q

As the path length increases, the attenuation coefficient of US in soft tissue

A

Remains the same

44
Q

Rayleigh scattering is related to frequency to the

A

4th power

45
Q

Scattering is directly related to

A

frequency (increased frequency=increased scattering)

46
Q

The two forms of reflection

A

specular and diffuse

47
Q

the half-value layer thickness is determined by

A

frequency and medium

48
Q

Thin half-value = media with

A

high attenuation rate

49
Q

Refraction only occurs if these 2 conditions are present

A

oblique incidence and 2 medium with different prop speeds

50
Q

List 3 processes that contribute to attenuation

A

reflection, scattering and intensity

51
Q

If attenuation causes a reduction in the intensity of a sound beam by 1/2 its original value, it is a

A

-3dB change

52
Q

Every 3dB increase means that the increase will be

A

double the intensity

53
Q

The attenuation coefficient __________________ as path length (depth) increases

A

stays the same

54
Q

Attenuation coefficient in blood is _____ than in soft tissue

A

lower

55
Q

What 3 things have the highest attenuation coefficient

A

air, lung and bone

56
Q

Acoustic impedance is calculated by multiplying the _____ by the _____ at which the sound travels in a medium

A

density and prop speed

57
Q

An ultrasound wave travels through soft tissue, hitting a boundary at a right angle. The 2 media have the same impedance. What percent of the sound beam has been refracted

A

0%

Vascular I & Physics I (19 decks)

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