# Week 5 - Reflection, Transmission, Refraction Flashcards

1
Q

What happens to sound beam’s energy when it enters tissue?

A

Some energy is reflected, some energy is transmitted, and some energy is changed.

2
Q

Most of the ultrasound energy is what?

A

changed to heat

3
Q

Describe a specular reflector?

A

a large, flat, smooth surface; with dimensions larger than the wavelength

4
Q

What is an example of a specular reflector?

A

the wall of an artery or vein

5
Q

What is incidence?

A

the angle the sound beam hits a specular reflector

6
Q

an angle of 90 degrees is know as __________

A

normal incidence

7
Q

When scanning a specular reflector, what angle gives you the clearest image?

A

90 degrees

8
Q

What technique can be used with the probe to obtain a normal incident angle?

A

heel and toe

9
Q

What influences how much energy is reflected at a perpendicular incident?

A

the difference of the tissues at the interface

10
Q

The ________ the difference in ___________ ___________ , the greater percentage of E that is reflected.

A

bigger, acoustic impedance

11
Q

What is an interface?

A

a boundary or border

12
Q

What is acoustic impedance?

A

a characteristic of tissue that affects the strength of an echo

13
Q

Proportion. Acoustic Impedance and density of tissue.

A

Directly

14
Q

Proportion. Acoustic impedance and speed of particle vibration.

A

Directly

15
Q

What is the unit of acoustic impedance?

A

Rayl

16
Q

What is the reflection coefficient?

A

% of wave strength that is reflected at an interface

17
Q

What are the 2 types of reflection coefficient?

A

Amplitude reflection coefficient and Intensity reflection coefficient

18
Q

What does ARC stand for?

A

Amplitude Reflection Coefficient

19
Q

What is ARC?

A

the percentage of the strength of the wave that is reflected at an interface

20
Q

What is the equation for ARC?

A

ARC% = (Z2 - Z1) / (Z2 + Z1)

21
Q

The _________ the difference in Z of two adjacent media, the greater the reflected percentage

A

larger

22
Q

What is the equation for IRC?

A

IRC% = [ (Z2 - Z1) / (Z2 + Z1) ] squared

23
Q

If 60% of the energy is reflected a normal incident, how much is transmitted?

A

40%

24
Q

When does diffuse reflection happen?

A

when the interface is not smooth

25
Q

the most important source of echoes in the body is what?

A

acoustic scattering

26
Q

What direction do scatterers reflect the beam?

A

all directions

27
Q

What is an example of a diffuse reflector?

A

a plaque surface

28
Q

What are two organs that can be described as scatterers?

A

the liver and the kidney

29
Q

What is a Rayleigh Scatterer?

A

a reflector that is MUCH smaller in size than the wavelength of the beam

30
Q

What is an example of a Rayleigh scatterer?

A

RBCs

31
Q

How do Rayleigh scatterers appear on screen? Why?

A

Black, because the echoes are scattered in all directions, therefore, very week echoes

32
Q

Rayleigh scattering is proportional to ________

A

frequency to the 4th power

33
Q

Areas of increased level of scattering compared to surrounding tissue will result in _________ echoes.

A

brighter

34
Q

When echoes appear brighter, they are know as __________.

A

hyperechoic

35
Q

Hypoechoic echoes appear _________.

A

darker

36
Q

term meaning “echoes present”

A

echogenic

37
Q

term meaning “no echoes”

A

echolucent

38
Q

homogeneous echoes will appear ___________.

A

similar in strength

39
Q

heterogeneous echoes will appear ___________.

A

bright and dark

40
Q

Refraction occurs when what happens?

A

an ultrasound beam meets an interface of tissues with different propagation speeds at a non-perpendicular angle

41
Q

Slow to fast C yields a __________ angle of transmission

A

higher

42
Q

Fast to slow C yields a __________ angle of transmission

A

lower

43
Q

State Snell’s law

A

sin (transmitted angle) / sin (incident angle) = C2 / C1

44
Q

a large, flat, smooth surface; with dimensions larger than the wavelength is a what?

A

specular reflector

45
Q

the wall of an artery or vein is what

A

an example of a specular reflector

46
Q

normal incidence = what?

A

90 degrees

47
Q

a characteristic of tissue that affects the strength of an echo is what?

A

acoustic impedance

48
Q

% of wave strength that is reflected at an interface

A

reflection coefficient

49
Q

what happens when the interface is not smooth

A

diffuse reflection

50
Q

a plaque surface is an example of what?

A

a diffuse reflector

51
Q

a reflector that is MUCH smaller in size than the wavelength of the beam

A

Rayleigh Scatterer

52
Q

darker echoes are _________

A

hypoechoic

53
Q

echogenic means what?

A

echoes are present

54
Q

echolucent means what?

A

no echoes present

55
Q

echoes that are similar in strength

A

homogeneous

56
Q

echoes that have bright and dark areas

A

heterogeneous

57
Q

a higher angle of transmission results from what?

A

Slow to fast C

58
Q

a lower angle of transmissions results from what?

A

Fast to slow C