review: Test2 Flashcards

1
Q

what is normal incidence?

(PORN)

A

perpendicular

orthogonal

right angle

ninety degrees

normal

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2
Q

if an angle is anything other than 90°, what is it known as?

A

oblique

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3
Q

acute

obtuse

A

acute-less than 90°

obtuse-more than 90°

both are oblique

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4
Q

the sound wave’s intensity right before it strikes a boundary is known as?

A

incident intensity

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5
Q

portion of the incident sound beam that, after striking a boundary, returns back is known as?

A

reflected intensity

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6
Q

normal incidence means that the incident sound beam strikes the boundary at what?

A

90°

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7
Q

the portion of the incident beam that, after striking a boundary, continues forward in the same general direction that it was traveling is what?

A

transmitted intensity

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8
Q

what is the percentage of ultrasound intensity that bounces back?

A

intensity reflection coefficient (IRC)

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9
Q

what is the percentage of ultrasound intensity that passesthrough the boundary?

A

intensity transmission coefficient (ITC)

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10
Q

What are the units of IRC and ITC?

A

no units-percentage

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11
Q

Large reflections will occur in normal incidence if the impedances are?

A

substantially different

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12
Q

with greater impedance, differences between two media, the IRC and the amount of reflection do what?

A

IRC increases

reflection is greater

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13
Q

specular reflection arrises from what type of interface?

A

a smooth boundary (mirror)

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14
Q

what do we know about oblique incidence?

A

oblique incidence occurs when the incident sound beam strikes the boundary at any angle other than 90°

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15
Q

two physical principles always apply to reflection with oblique incidence:

A

1) conservation of energy
2) reflection angle = incident angle

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16
Q

what is Snell’s law?

A

quantifies the physics of refraction

sin(transmission angle)/sin(incident angle) = speed of medium2/speed of medium1

medium1-defined as the medium in which the sound is currently traveling

medium2-defined as the medium into which the sound is entering

17
Q

what is a reflection that arises from a rough boundary?

A

diffuse reflection (backscatter)

18
Q

what is considered a dominant contributor to attenuation?

A

absorption

19
Q

as path length increases, attenuation of ultrasound in soft tissue does what?

20
Q

acoustic impedance is also known as:

A

characteristic impedance

21
Q

in order to have reflections occur, what do we have to have?

A

media on either side of the boundary have different impedances

22
Q

what type of probe would you use for abd images vs small parts?

A

higher frequency on parts closer to surface

lower frequency on parts that are deeper in the body

23
Q

what is the attenuation coefficient for soft tissue?

A

0.5 dB/cm/MHz

24
Q

how do we determine attenuation?

A

determined by 2 factors:

path length, frequency of sound

25
decibels and intensities
3dB-double 10dB-ten times larger - 3dB-half - 10dB-one tenth
26
what's the difference between more and less attenuation in regards to frequency and distance?
more attenuation: longer distances, higher frequencies less attenuation: shorter distances, lower frequencies
27
what is sound going in all different directions?
scattering
28
sound back to the transducer is created by:
reflection: specular(mirror), diffuse(backscatter)
29
what is Rayleigh scattering related to?
organized and omnidirectional Rayleigh scattering always equals frequency4 when frequency doubles, Rayleigh scattering is 16 times greater
30
what is the calculation for acoustic impedance?
acoustic impedance = density(of a medium) x speed(at which sound travels in medium) units-rayls(z)