Lesson 10

Question 1

What does perpendicular incidence involve? (3)

Answer 1

1. Pulse echo techniques
2. Transmission
3. Impedance differences

Question 2

What does oblique incidence involve? (5)

Answer 2

1. Angle of incidence
2. Angle of reflection
3. Angle of transmission
4. Refraction
5. Propagation speed

Question 3

What does relfection and transmission depend on?

Answer 3

Impedance

Question 4

What does refraction depend on?

Answer 4

Propagation speed

Question 5

What happens to the echoes when a surface is rough?

Answer 5

It scatters

Question 6

What are examples of specular reflection? (2)

Answer 6

1. Perpendicular incidence

2. Oblique incidence

Question 7

Specular reflector

Answer 7

Mirror like

Question 8

What are examples of specular reflectors in the human body?

Answer 8

Smooth, large boundaries

- sound will bounce back to the transducer and produce a strong echo

Question 9

What is an example of not smooth/rough surfaces?

Answer 9

Heterogeneous tissues

- eg) liver tissue

Question 10

When do you get scatter? (2)

Answer 10

1. In heterogenous tissues

2. When the target object is comparable or smaller than the wavelength

Question 11

What do you get when a small wavelength hits a larger object?

Answer 11

Specular reflection

Question 12

Does scattering help us?

Answer 12

Yes

• most times
• but typically want less scattering

Question 13

What does scattering help us with?

Answer 13

Getting a good visual of the tissue parenchyma

Question 14

What does scattering depend on? (2)

Answer 14

1. Frequency

2. Scatter size

Question 15

What happens to scattering if you increase the frequency?

Answer 15

Will result in a decrease in wavelength and therefor have a decrease scattering

Question 16

Backscatter

Answer 16

The echo information that comes back to the transducer

Question 17

What happens with scattering in Rayleigh scattering as frequency increases?

Answer 17

Scattering increases

Question 18

What is scattering intensity proportional to in Rayleigh scattering?

Answer 18

Frequency

Question 19

What happens with scattering in Rayleigh scattering if you increase wavelength?

Answer 19

Frequency decreases which means scattering decreases

Question 20

What is an example of a speckle?

Answer 20

Scattering

Question 21

Scattering

Answer 21

Echo sound waves take different paths on the way back to the transducer

Question 22

What 2 ways can waves come back from scattering?

Answer 22

1. Constructively

2. Destructively

Question 23

Constructively speckle

Answer 23

The scatters reinforce each other

- adding 2 sound waves together

Question 24

Destructively

Answer 24

The scatters partially (dont fully line up) or totally cancel each other
- they dont line up

Question 25

What is another word for constructive interface?

Answer 25

In phase

Question 26

What is another word for destructive interference?

Answer 26

Out of phase

Question 27

What happens to the frequency if you double the transducer?

Answer 27

It goes up 16x

Question 28

What appearance do speckles give off?

Answer 28

Grainy appearance

Question 29

Acoustic speckle

Answer 29

A form of acoustic noise

Question 30

What is acoustic speckle a result of?

Answer 30

Constructive and destructive interference of scattered sound waves