Lesson 7 Flashcards
What 3 things make up attenuation?
- Absorption
- Reflection
- Scattering
Attenuation
Weakening of sound
What is the result of weaker signals?
Weaker echoes
What structures produce weaker signals?
Structures that are farther away
Where is the near field?
Closest are to the transducer
Where is the mid field?
Between the near field and the far field
Where is the far field?
Farthest area to the transducer
What happens to sound as it goes through a medium?
It gets weaker
- has to go through and come back
What do we use that can fix attenuation?
TGC
What does TGC stand for?
Time gain compensation
Whats another word for TGC?
DGC
What does DGC stand for?
Depth gain compensation
What does the TGC slope provide?
Amplification of specific field echoes
What does TGC do?
It amplifies the far field to promote uniform in tissues
- eg) liver
What does it mean when your TGC is straight on the ultrasound machine?
You are getting equal amounts of amplification
What does it mean when your TGC is on a diagonal on the machine?
You get amplification in different spots
- leads to a more uniform image
What is the formula for attenuation in soft tissues?
a = 1/2f x L a = attenuation f = frequency L = length/distance/thickness
How does attenuation occur in soft tissues?
- 5 there and 0.5 back = 1
- dB/cm x MHz
- compensates for both directions
What 2 things does overall gain do?
- Amplification of entire field of view
2. Amplification of all incoming echo voltages
What is attenuation’s unit?
Decible
- dB
How much is 3db? (2)
- 1/2x
2. 2x
How much is 10dB? (2)
- 1/10x
2. 10x
Define decible
The ratio between 2 intensities
What is the formula for attenuation in normal tissue?
a = ac x L a = attenuation ac = attenuation coefficient L = length/distance
What is the formula for attenuation coefficient?
ac = 1/2f ac = attenuation coefficient f = frequency
Half value layer
The thickness of material that will halve the original intensity
- the distance it takes to drop 3dB
