Lesson 10 Flashcards
What does perpendicular incidence involve? (3)
- Pulse echo techniques
- Transmission
- Impedance differences
What does oblique incidence involve? (5)
- Angle of incidence
- Angle of reflection
- Angle of transmission
- Refraction
- Propagation speed
What does relfection and transmission depend on?
Impedance
What does refraction depend on?
Propagation speed
What happens to the echoes when a surface is rough?
It scatters
What are examples of specular reflection? (2)
- Perpendicular incidence
2. Oblique incidence
Specular reflector
Mirror like
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?
Heterogeneous tissues
- eg) liver tissue
When do you get scatter? (2)
- 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?
Specular reflection
Does scattering help us?
Yes
- 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)
- Frequency
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
Backscatter
The echo information that comes back to the transducer
What happens with scattering in Rayleigh scattering as frequency increases?
Scattering increases
What is scattering intensity proportional to in Rayleigh scattering?
Frequency
What happens with scattering in Rayleigh scattering if you increase wavelength?
Frequency decreases which means scattering decreases
What is an example of a speckle?
Scattering
Scattering
Echo sound waves take different paths on the way back to the transducer
What 2 ways can waves come back from scattering?
- Constructively
2. Destructively
Constructively speckle
The scatters reinforce each other
- adding 2 sound waves together
Destructively
The scatters partially (dont fully line up) or totally cancel each other
- they dont line up
What is another word for constructive interface?
In phase
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?
Grainy appearance
Acoustic speckle
A form of acoustic noise
What is acoustic speckle a result of?
Constructive and destructive interference of scattered sound waves
