Chapters 6-7 Flashcards Preview

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Flashcards in Chapters 6-7 Deck (70):
1

Define attenuation

weakening of sound as it travels

2

What is the log of 1,000?

3
we multiply 10 by itself 3 times

3

What unit is used to quantify the strength of sound beams as they are created?

decibels

4

What do positive decibels report?

they report signal that are increasing in strength

5

Decibels report what?

relative changes verses measurement of absolute numbers

6

How many intensities does dB require?

2

7

What are the four components of decibel notation?

a relative measurement
a comparison
a ration
logarithmic

8

what does -3dB mean?

1/2 of intensity

9

What does 10dB mean?

10x larger

10

What do negative decibels report?

they describes signals that are decreasing in strength or getting smaller

11

What are the two factors attenuation is determined by?

path length and freq

12

The decrease in amplitude, intensity, and power as sound travels is what?

attenuation

13

How are distance and attenuation related?

directly

14

How are frequency and attenuation related?

directly

15

What are the three components of attenuation?

reflection, scattering, and absorption

16

What is reflection?

as sound strikes a boundary, a portion of the waves energy may be redirected, or reflected, back to the sound source

17

What are two forms of reflection?

specular and diffuse (nonspecular)

18

Define specular reflection

when the boundary is smooth, the sound is reflected in only one direction in an organized manner.

19

True or false: specular reflections at an angle do return to the transducer

false
they do not

20

Another name for diffuse reflection

backscatter

21

Define diffuse reflection

not smooth and the wave reflects off an irregular surface, and radiate in more than one direction

22

What is an advantage of diffuse reflection?

some interfaces at suboptimal angles to the sound beam can still produce reflections that will return to the transducers

23

Define scattering

the random redirection of sound in many directions

24

How is scattering and freq related?

directly

25

When does sound scatter?

sound scatters when the tissue interface is small; that is equal to or less than the wavelength of the incident sound beam

26

Define rayleigh scattering

a special form of scattering that occurs when the structure dimensions are much smaller than the beams wavelength
redirects the sound beam equally in all directions

27

What is an example of rayleigh scattering?

the interaction of ultrasound and red blood cells

28

How is freq and rayleigh scattering related?

scattering is related to freq raised to the fourth power
freq4

29

Define absorption

the conversion of sound into heat

30

How is absorption and frequency related?

directly

31

What is the attenuation coefficient?

the number of decibels of attenuation that occurs when sound travels one centimeter
dB/cm

32

What is the formula for total attenuation?

dB= atten coeff (dB/cm) x distance (cm)

33

How is the attenuation coefficient calculated?

1/2freq

34

How is attenuation coefficient and freq related?

directly

35

What are the mediums that have the lowest attenuation to the highest?

water, blood (urine, biologic fluids), fat, soft tissue, muscle, bone and lung and air (the highest is air)

36

What is the half-value layer thickness?

the distance sound travels in a tissue that reduces the intensity of sound to one half its original value or 3dB
units length, cm

37

What are synonyms for half value layer?

penetration depth, depth of penetration and half boundary layer

38

What are two factors half value layer thickness depend on?

the medium, and freq of sound

39

What two factors play a role in a thin half value?

high freq sound and a media with high attenuation rate

40

What two factors play a role in a thick half value?

low freq sound and a media with low attenuation rate

41

Define impedance

the acoustic resistance to sound traveling in a medium

42

What is the formula for impedance?

rays= density x prop. speed

43

What are typical values for impedance?

1,250,000- 1,750,000 rayls

44

What is the relationship between attenuation and propagation speed?

unrelated

45

What is the relationship between freq and depth of penetration?

inverse

46

What are the three types of angles?

acute
right
obtuse

47

What are synonyms for normal incidence?

perpendicular
orthogonal
right angle
90 degree
*Remember PORN

48

What is oblique incidence?

occurs when the incident sound beam strikes the boundary at any angle other than 90 degrees
AKA non-perpendicular

49

What is the incident intensity?

the sound waves intensity immediately before it strikes a boundary

50

What is the reflected intensity?

the intensity of the portion of the incident sound beam that after striking a boundary, returns back from where it came

51

What is transmitted intensity?

intensity that after striking a boundary continues forward in the same general direction that it was traveling

52

What is the formula for incident (starting) intensity?

=reflected intensity + transmitted intensity

53

What is the IRC?

intensity reflection coefficient= the percentage of the intensity that bounces back when a sound beam strikes the boundary between two media

54

Very little sound is reflected between what two boundaries?

soft tissue/soft tissue
or organ parenchyma/ organ parenchyma

55

What is the ITC?

intensity transmission coefficient= the percentage of intensity that passes in the forward direction when the beam strikes an interface between two media

56

What must happen for reflection with normal incidence to occur?

90 degrees and different impedances

57

When will no reflection occur?

when two medias have the same impedances

58

When is all sound transmitted?

when two medias have the same impedances

59

What is the formula for ITC?

=1-IRC

60

What two physical principles apply to reflection with oblique incidence?

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

61

conservation of sound must equal what?

100%

62

Define refraction

the change in direction of wave propagation when traveling from one medium to another

63

When does refraction occur?

1. oblique incidence
2. different propagation speeds of two media

64

What does Snells law refer to?

refraction

65

What is the relationship between the time of flight to depth?

directly

66

What is the range equation?

depth (mm)=(1.54 x go return time)/2

67

What is the total distance for time of flight of 39 microseconds?

6 cm
39/13=3, there and back is 6 cm

68

What is the formula for PRP for the range equation?

PRP= imaging depth (cm) x 13 ms/cm

69

What is the relationship between PRP and max, imaging depth?

direct

70

What is the relationship between PRF and max, imaging depth?

inverse