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vascular anatomy > Physics review Test 2 > Flashcards

Physics review Test 2 Flashcards

1
Q

What happens to sound waves as they propagate in a medium?

A

They weaken.

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2
Q

What does attenuation mean ?

A

The loss of energy. Decrease in intensity, power and amplitude.

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3
Q

What two factors is attenuation determined by ?

A

Path length

Frequency of sound.

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4
Q

How are distance and attenuation related?

A

They are directly related.

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5
Q

How are frequency and attenuation related?

A

They are directly related.

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6
Q

What is attenuation measured in ?

A

Db

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7
Q

The more attenuation you have, the _______ the distance and the higher the _______.

A

Longer, frequencies.

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8
Q

The less attenuation you have, the _______ the distance and the lower the ________.

A

shorter, frequencies.

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9
Q

What three processes contribute to attenuation ?

A

reflection, scattering, absorption.

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10
Q

As a sound strikes a boundary, a portion of the wave’s energy may be redirected or _______.

A

Reflected

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11
Q

Name two forms of reflection.

A

specular & diffuse

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12
Q

What type of reflection is smooth, and reflected only in one direction in an organized manner?

A

Specular reflection.

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13
Q

Name one limitation for a specular reflector.

A

once the wave is slightly off axis, the reflection does not return to the transducer.

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14
Q

When a wave reflects off an irregular surface, it radiates in more than one direction, this form of reflection is called ________.

A

diffuse reflection or backscatter.

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15
Q

What is an advantage of diffuse reflections ?

A

interfaces at sub optimal angles to the sound beam can still produce reflections that will return to the transducer.

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16
Q

What is a disadvantage of diffuse reflections?

A

they have a lower strength than specular reflections.

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17
Q

What is scattering in ultrasound ?

A

the random redirection of sound in many directions.

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18
Q

What scatters more, higher frequency sound beams or lower?

A

Higher frequency.

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19
Q

How is scattering related to frequency?

A

directly related.

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20
Q

When does Rayleigh scattering happen?

A

occurs when the structures dimensions are much smaller than the beam’s wavelength.

21
Q

In clinical imaging, the interaction of ultrasound and red blood cells results in ___________.

A

Rayleigh scattering

22
Q

Mathematically, scattering is related to frequency raised to the ______ power.

A

fourth

23
Q

what type of reflection sends sound back to the transducer, and is organized?

A

specular reflection.

24
Q

What type of reflection sends sound back to the transducer but is disorganized?

A

diffuse or backscatter.

25
Q

What type of reflection sounds sound in all directions, and is organized?

A

Rayleigh scattering.

26
Q

What type of reflector sends sound in all directions and is disorganized?

A

Scattering.

27
Q

What is the third and most sizeable component of attenuation ?

A

absorption

28
Q

what is absorption?

A

occurs when ultrasonic energy is converted into another energy, such as heat.

29
Q

How do you report attenuation, in ultrasound?

A

by calculating attenuation coefficient

30
Q

What is the attenuation coefficient ?

A

is the number of decibels of attenuation that occurs when sound travels one cm.

31
Q

What are the units of attenuation coefficient?

A

db/cm

32
Q

What is the equation for total attenuation?

A

total attenuation= attenuation coefficient (db/cm) * distance (cm)

33
Q

What is half-value layer thickness?

A

is the distance that sounds travel in a tissue that reduces the intensity of a sound to one-half its original value.

34
Q

Whats another way that half-value layer thickness can be described ?

A

depth of a tissue that results in 3 db of attenuation to the intensity.

35
Q

The half- value layer is _____ for tissues that attenuate sound a great deal, such as lung or bone.

A

thin

36
Q

high frequency sound results in a _____ half-value layer.

A

thin

37
Q

Lower frequency sound results in a _____ half-value layer.

A

Thick

38
Q

In clinical imaging half- value layers ranges from ___ to ___.

A

0.25 to 1.0 cm.

39
Q

What other names are half value layer known by

A

Penetration depth, depth of penetration, half-boundary layer.

40
Q

The half -value layer thickness depends on what two factors?

A

the medium and the frequency of sound

41
Q

What is impedance ?

A

Acoustic resistance to sound traveling in a medium.

42
Q

How do you calculate impedance ?

A

Z= P*C

43
Q

Reflection of an ultrasound wave depends upon what differences?

A

the difference in acoustic impedance’s of the two media at a boundary.

44
Q

Impedance is determined by the ________ only.

A

Medium

45
Q

Acoustic impedance is also called __________.

A

characteristic impedance

46
Q

Impedance is reported in the units of _________.

A

rayls

47
Q

What does normal incidence mean ?

A

That the incident sound beam strikes the boundary at exactly 90 degrees.

48
Q

What does oblique incidence mean ?

A

That the incident sound beam strikes the boundary at any angle other than 90 degrees.

vascular anatomy (7 decks)

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