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

Ch. 6 Physics Flashcards

(57 cards)

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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

24
Q

Incident intensity=

Study These Flashcards
A

reflected intensity + transmitted intensity

25
The intensity of a sound beam that returns after striking a boundary
reflected intensity
26
The intensity of a sound beam that continues forward after striking a boundary
transmitted intensity
27
Sound wave intensity before it strikes a boundary
incident intensity
28
When incident angle of sound beam strikes a boundary at any angle other than 90 degrees
oblique incidence
29
IRC% + ITC%=
100%
30
% of US intensity that bounces back when beam hits a boundary between 2 media
intensity reflection coefficient (IRC)
31
Amount of ultrasound intensity reflected at a boundary in soft tissue
less than 1%
32
% of US intensity that continues when beam strikes interface between 2 media
intensity transmission coefficient (ITC)
33
Amount of ultrasound intensity transmitted at a boundary in soft tissue
>99%
34
US beam strikes a tissue boundary at a 90 degree angle is called
normal incidence
35
If an ultrasound beam strikes a tissue boundary at any angle other than 90 degrees it is
oblique incidence
36
When the transmission angle is greater or less than the incident angle what happens
refraction
37
Quantification of the physics of refraction
snell's law
38
Occurs only if these two conditions are present - oblique incidence and different prop speeds. Causing "bending" of the sound beam
refraction
39
With oblique incidence, the reflection angle equals
incident angle
40
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
normal incidence
41
Units for measuring impedance
rayls
42
Units of intensities
w/cm squared & time and space
43
As the path length increases, the attenuation coefficient of US in soft tissue
Remains the same
44
Rayleigh scattering is related to frequency to the
4th power
45
Scattering is directly related to
frequency (increased frequency=increased scattering)
46
The two forms of reflection
specular and diffuse
47
the half-value layer thickness is determined by
frequency and medium
48
Thin half-value = media with
high attenuation rate
49
Refraction only occurs if these 2 conditions are present
oblique incidence and 2 medium with different prop speeds
50
List 3 processes that contribute to attenuation
reflection, scattering and intensity
51
If attenuation causes a reduction in the intensity of a sound beam by 1/2 its original value, it is a
-3dB change
52
Every 3dB increase means that the increase will be
double the intensity
53
The attenuation coefficient __________________ as path length (depth) increases
stays the same
54
Attenuation coefficient in blood is _____ than in soft tissue
lower
55
What 3 things have the highest attenuation coefficient
air, lung and bone
56
Acoustic impedance is calculated by multiplying the _____ by the _____ at which the sound travels in a medium
density and prop speed
57
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
0%

Vascular I & Physics I (19 decks)

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