# Physics Ch. 6

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1. Attenuates
sound weakens as it travels in the body
2. Amplified
stregnthening of soundwave that is converted to electricity
3. decibel notation
standard mesaurement tool used to report changes in sound
4. logarithm of 1000
3

basically how many zeros for even powers of ten
5. decibels report what kind of changes
relative not absolute
6. decibels need how many intensities
2 compared (ratio)

actual level/starting level
7. decibels

1/2
1/10

double
ten times
• -3
• -10

• 3
• 10
8. attenuation
weakening of intensity power and amplitude
9. two factors for attenuation
depth

frequency

Directly Related
10. how is attenuation measured
decibels

omit negative sign
11. 3 attenuation processes
• reflection (specular diffuse)
• scattering (rayleigh)
• absorption
12. absorption

relaxation time
• primary component of attenuation
• sound energy turns to heat (vibration of particles/friction)
• bone has a lot of absorption

relaxation time- time for particles to go back to equalibrium

RT and absorption directly related
13. reflection
• redirecting wave back to sound source
• wave is weakened
14. two typed of reflection
specular and diffuse
15. reflection boundary
greater than a few wavelegnths in size
16. specular
boundary
pattern
angle of incidence =
off axis beam
color on US
eg.
• boundary-greater than a wavelegnth
• large and smooth
• pattern- organized reflects in one direction
• angle of incidence = angle of reflection
• off axis beam will not come back to transducer
• color is white- strong reflection
• eg. blood vessle wall
17. Diffuse (nonspecular, backscatter)
boundary
pattern
off axis beam
color
eg.
• boundary- greated than a wavelegnth
• Small and Rough
• Disorganized
• pattern- unpredictable come back in gen direction
• off axis beam- not reflected (may come back to transducer)
• color med gray
• eg. hepatocyte
18. Acoustic Impedance
definition and symbol
units
determined by s or m
• resistance to sound travel
• z
• rayls
• medium
19. impedance and reflection
must have different I for reflection to occur

bigger difference in I more reflection
20. Impedance of tissue
How WELL it travels. not how fast
• air .0004
• fat
• water
• blood
• kidney
• soft tissue 1.63
• liver
• muscle
• bone 7.8 (fast but not well)
21. impedence formula
z= p x c

Impedence = density x prop speed
22. Scattering
definition
• random redirection of sound in many directions
• toward and away from transducer
23. scattering
boundary
= or less than a wavelegnth in size
24. scattering relationship to frequency
• directly related
• increase frequency increase scattering
25. Rayleigh Scattering
Boundary
• very small
• much smaller than a wavelegnth
26. Rayleigh Scattering
organized or disorganized
pattern
eg
look on US
• organized
• equal in all directions
• redblood cell
• weak reflectors- look black
27. Rayleigh Scattering is dramatically effected by
• Frequency
• mathmatical relationship of F4
28. Attenuation of media low to high

(women fight fat some men buy lunch alone)
• water low
• fluid
• fat
• soft tissue
• muscle
• bone
• lung
• air high
29. sound back to the transducer
30. sound in all directions
• rayleigh scattering- organized
• scattering -disorganized
31. attenuation coefficient
definition
units
• amount of attenuation the sound beam gives up for each cm it travels through tissue
• decibels/cm
32. does atten change through tissue
no stays same
33. Medium
• Prop Speed
• Impedance
• Atten Co
34. Total Attenuation formula
Total Attenuation = Atten. Coefe. x distance
35. attenuation coef formula
atten. coef. = frequency/ 2

Soft tissue = .5-.7 d/cm MHz
36. Half layer thickness
synonyms
• half intensity depth
• depth of penetration
37. half layer thickness
definition
units
• depth in tissue sound travels that results in 3db of intensity attenuation
• cm
38. half layer thickness formula
= 3/Attenuation Coef.
39. half layer thickness depends on
frequency and tissue/medium
40. half layer thickness in soft tissue
=6/f
41. Angles of Incidence
normal names
• perpendicular
• othogonal
• right
• ninety
42. angles of incidence not normal
oblique
43. sound wave is either
transmitted or reflected
44. 3 intensities at a boundary
• incident intensity- right before
• reflected intensity- redirected
• transmitted intensity- continues in same direction
45. incident intensity =
• refected intensity + transmitted intensity
• conservatin of energy
46. inorder for reflection must have different
I - Impedance (z)
47. Intensity Coeffiencient
units
2 coefficients
• %
• IRC and ITC (reflected and transmitted)
48. intensity coefficient formula
100% = IRC + ITC
49. % of reflection and echo stregnth of
soft tissue
bone
air
• st- 1% or less
• b- 50% (think of fetal skull we see through)
• a- 100%- strong echo
50. oblique incidence reflection
cannot predict if sound will reflect or transmit
51. formula for reflection with normal incidence with 2 different impedences of medium
IRC% = [z2 - z1 / z2 + z1]2 x 100

• minus / plus
• z2 first
52. Intensity transmission Coefficient formula
• ITC %= transmitted int/ incident int x 100
• or = 1- IRC
53. 2 principles apply with oblique incidence
• conservation of energy
• reflection angle = incident angle (Luez's law)
54. Refraction
definition
two conditions
bending of transmitted wave

must have oblique incidence and differenct prop speeds
55. snells law
transmission angel/ incident angel= speed of med 2/ speed of med 1

whichever med has a greated trans angle has a greated speed
56. Reflection- difference in
Z or impedance
57. refraction- deffence in
c or prop speed
58. conversion of sound to heat
absorption
59. db one hundred fold increase
20db
6db
61. organized in one direction
specular
62. disorganized and in general direction of source
diffuse
63. chaotic and in all directions toward and away
scatterer
64. organized in all directions
rayleigh scatterer
65. formula for calculating db
current intensity/ original intensity
66. smooth and larger than a few wavelegnths
specular
67. rough and larger than a few wavelegnths
diffuse backscatter nonspect
68. equal or less than a wavelegnth
scatterer
69. much smaller than a wavelegnth
rayleigh scatterer
70. contributers to attenuation
• refletion
• scattering
• absorption
71. reflection of diffuse reflecter effected by off axis beam t or f
f