Chapter 6 Flashcards

1
Q

Positive decibels

A

indicate that the signal strengthened (final intensity > initial intensity)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Negative Decibels

A

indicate that the signal has weakened (final intensity < initial intensity)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

3 dB intensity ratio 2 intensity doubled
6 dB intensity ratio 4 intensity increase 4 fold
9 dB intensity ratio 8 intensity increase 8 fold
10 dB intensity ratio 10 intensity increase 10 fold
20 dB intensity ratio 100 intensity increase 100 fold
30 dB intensity ratio 1000 intensity increase 1000 fold
40 dB intensity ratio 10000 intensity increase 10,000 fold

A

Intensity ratios

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Attenuation

A

The decrease in intensity, power and amplitude as sound travels
expressed in dB

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Attenuation is determined by two factors

A
  1. Path length or distance traveled by the sound wave
  2. Frequency of sound
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Path length and attenuation are directly related

A

Path Length ∝ Attenuation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Frequency and attenuation are directly related

A

Frequency ∝ attenuation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Three processes contribute to attenuation

A

Reflection
Scattering
Absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Reflection

A

a portion of the sound wave is redirected back towards the sound source when it strikes a boundary between 2 medium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

There are two forms of reflection

A
  1. Specular
  2. Diffuse
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Specular reflection

A

is when the sound is reflected off the boundary back towards the probe in only one direction in an organized manner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

One limitation of specular reflectors

A

is that once the wave is slightly off axis (non perpendicular to the boundary) the reflection does not return to the transducer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

An advantage of diffuse reflections

A

is that the transducer receives reflections from interfaces that it is not perpendicular to

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

a second advantage to backscatter

A

is that heterogeneous tissue acts as a back scatter and allows us to see tissue texture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

A disadvantage to backscatter

A

is that backscattered signals have lower strength than specular reflections

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Scattering

A

is the random redirection of sound in many different directions

17
Q

Disadvantage to Scattering

A

Little to none of the redirected sound wave makes it back to the probe

18
Q

Rayleigh scattering

A

is a special type of scattering that occurs when the interface/structure diameter is much smaller than the wavelength
Sound is redirected equally in all directions (little towards probe)

19
Q

Disadvantage to Rayleigh Scattering

A

Little to none of the redirected sound wave makes it back to the probe

20
Q

Rayleigh scattering ∞ frequency4

A

rayleigh scattering is directly related to frequency quadrupled

21
Q

Absorption

A

occurs when ultrasonic energy is converted into another energy form such as heat

22
Q

absorption is directly related to frequency

A

absorption ∝ frequency

23
Q

Attenuation Coefficient

A

is the number of decibels of attenuation that occurs when sound travels one centimeter; units = dB/cm

24
Q

Attenuation Coefficient is directly related to frequency

A

attenuation coefficient ∝ frequency

25
Half Value Layer Thickness
is the distance that sound travels in a tissue that reduces the intensity of sound to one-half its original value
26
Acoustic Impedance
it is the resistance offered to sound traveling through the medium AKA: characteristic impedance
27
Acoustic Impedance
is a characteristic of the tissue, specifically it is the resistance offered to sound traveling through the medium AKA characteristic impedance units of rayls typical values are 1.25-1.75 Mrayls
28
Incidence
the angle at which the wave strikes the boundary
29
Normal incidence
is when the incident sound beam strikes the boundary at exactly 90° Also called perpendicular, orthogonal, right angle, or 90 degree incidence
30
Oblique incidence
is when the incident sound beam strikes the boundary at an angle other than 90° Also called nonperpendicular incidence
31
Incident intensity
is the sound wave’s intensity immediately before it strikes a boundary
32
Reflected Intensity
is the intensity of the reflected portion of the sound wave, immediately after it reflects off the boundary
33
Transmitted Intensity
is the intensity of the transmitted portion of the sound wave immediately after it crosses the boundary
34
Intensity Reflection Coefficient
The percentage of the intensity that is reflected back when a sound beam strikes the boundary between two media
35
Intensity Transmission Coefficient
The percentage of the intensity that propagates forward or is transmitted when the beam strikes the interface between two media
36
In oblique incidence if we have reflection the
incident angle = reflection angle
37
Refraction
the soundwave may bend or change direction as it crosses the boundary
38
Refraction occurs only if two conditions are satisfied; you must have
1. Oblique incidence 2. Different propagation speeds between the 2 media
39
the critical angle
The incident angle at which no transmission into the second medium takes place (>t = 90 degrees)