Flashcards in Lesson 10 Deck (30)
What does perpendicular incidence involve? (3)
1. Pulse echo techniques
3. Impedance differences
What does oblique incidence involve? (5)
1. Angle of incidence
2. Angle of reflection
3. Angle of transmission
5. Propagation speed
What does relfection and transmission depend on?
What does refraction depend on?
What happens to the echoes when a surface is rough?
What are examples of specular reflection? (2)
1. Perpendicular incidence
2. Oblique incidence
What are examples of specular reflectors in the human body?
Smooth, large boundaries
- sound will bounce back to the transducer and produce a strong echo
What is an example of not smooth/rough surfaces?
- eg) liver tissue
When do you get scatter? (2)
1. In heterogenous tissues
2. When the target object is comparable or smaller than the wavelength
What do you get when a small wavelength hits a larger object?
Does scattering help us?
- most times
- but typically want less scattering
What does scattering help us with?
Getting a good visual of the tissue parenchyma
What does scattering depend on? (2)
2. Scatter size
What happens to scattering if you increase the frequency?
Will result in a decrease in wavelength and therefor have a decrease scattering
The echo information that comes back to the transducer
What happens with scattering in Rayleigh scattering as frequency increases?
What is scattering intensity proportional to in Rayleigh scattering?
What happens with scattering in Rayleigh scattering if you increase wavelength?
Frequency decreases which means scattering decreases
What is an example of a speckle?
Echo sound waves take different paths on the way back to the transducer
What 2 ways can waves come back from scattering?
The scatters reinforce each other
- adding 2 sound waves together
The scatters partially (dont fully line up) or totally cancel each other
- they dont line up
What is another word for constructive interface?
What is another word for destructive interference?
Out of phase
What happens to the frequency if you double the transducer?
It goes up 16x
What appearance do speckles give off?
A form of acoustic noise