Week 5 - Reflection, Transmission, Refraction

Question 1

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

Answer 1

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

Question 2

Most of the ultrasound energy is what?

Answer 2

changed to heat

Question 3

Describe a specular reflector?

Answer 3

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

Question 4

What is an example of a specular reflector?

Answer 4

the wall of an artery or vein

Question 5

What is incidence?

Answer 5

the angle the sound beam hits a specular reflector

Question 6

an angle of 90 degrees is know as __________

Answer 6

normal incidence

Question 7

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

Answer 7

90 degrees

Question 8

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

Answer 8

heel and toe

Question 9

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

Answer 9

the difference of the tissues at the interface

Question 10

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

Answer 10

bigger, acoustic impedance

Question 11

What is an interface?

Answer 11

a boundary or border

Question 12

What is acoustic impedance?

Answer 12

a characteristic of tissue that affects the strength of an echo

Question 13

Proportion. Acoustic Impedance and density of tissue.

Answer 13

Directly

Question 14

Proportion. Acoustic impedance and speed of particle vibration.

Answer 14

Directly

Question 15

What is the unit of acoustic impedance?

Answer 15

Rayl

Question 16

What is the reflection coefficient?

Answer 16

% of wave strength that is reflected at an interface

Question 17

What are the 2 types of reflection coefficient?

Answer 17

Amplitude reflection coefficient and Intensity reflection coefficient

Question 18

What does ARC stand for?

Answer 18

Amplitude Reflection Coefficient

Question 19

What is ARC?

Answer 19

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

Question 20

What is the equation for ARC?

Answer 20

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

Question 21

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

Answer 21

larger

Question 22

What is the equation for IRC?

Answer 22

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

Question 23

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

Answer 23

40%

Question 24

When does diffuse reflection happen?

Answer 24

when the interface is not smooth

Question 25

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

Answer 25

acoustic scattering

Question 26

What direction do scatterers reflect the beam?

Answer 26

all directions

Question 27

What is an example of a diffuse reflector?

Answer 27

a plaque surface

Question 28

What are two organs that can be described as scatterers?

Answer 28

the liver and the kidney

Question 29

What is a Rayleigh Scatterer?

Answer 29

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

Question 30

What is an example of a Rayleigh scatterer?

Answer 30

RBCs

Question 31

How do Rayleigh scatterers appear on screen? Why?

Answer 31

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

Question 32

Rayleigh scattering is proportional to ________

Answer 32

frequency to the 4th power

Question 33

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

Answer 33

brighter

Question 34

When echoes appear brighter, they are know as __________.

Answer 34

hyperechoic

Question 35

Hypoechoic echoes appear _________.

Answer 35

darker

Question 36

term meaning "echoes present"

Answer 36

echogenic

Question 37

term meaning "no echoes"

Answer 37

echolucent

Question 38

homogeneous echoes will appear ___________.

Answer 38

similar in strength

Question 39

heterogeneous echoes will appear ___________.

Answer 39

bright and dark

Question 40

Refraction occurs when what happens?

Answer 40

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

Question 41

Slow to fast C yields a __________ angle of transmission

Answer 41

higher

Question 42

Fast to slow C yields a __________ angle of transmission

Answer 42

lower

Question 43

State Snell's law

Answer 43

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

Question 44

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

Answer 44

specular reflector

Question 45

the wall of an artery or vein is what

Answer 45

an example of a specular reflector

Question 46

normal incidence = what?

Answer 46

90 degrees

Question 47

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

Answer 47

acoustic impedance

Question 48

% of wave strength that is reflected at an interface

Answer 48

reflection coefficient

Question 49

what happens when the interface is not smooth

Answer 49

diffuse reflection

Question 50

a plaque surface is an example of what?

Answer 50

a diffuse reflector

Question 51

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

Answer 51

Rayleigh Scatterer

Question 52

darker echoes are _________

Answer 52

hypoechoic

Question 53

echogenic means what?

Answer 53

echoes are present

Question 54

echolucent means what?

Answer 54

no echoes present

Question 55

echoes that are similar in strength

Answer 55

homogeneous

Question 56

echoes that have bright and dark areas

Answer 56

heterogeneous

Question 57

a higher angle of transmission results from what?

Answer 57

Slow to fast C

Question 58

a lower angle of transmissions results from what?

Answer 58

Fast to slow C