Lesson 7 Flashcards Preview

Physics 1 > Lesson 7 > Flashcards

Flashcards in Lesson 7 Deck (26)
Loading flashcards...
1

What 3 things make up attenuation?

1. Absorption
2. Reflection
3. Scattering

2

Attenuation

Weakening of sound

3

What is the result of weaker signals?

Weaker echoes

4

What structures produce weaker signals?

Structures that are farther away

5

Where is the near field?

Closest are to the transducer

6

Where is the mid field?

Between the near field and the far field

7

Where is the far field?

Farthest area to the transducer

8

What happens to sound as it goes through a medium?

It gets weaker
- has to go through and come back

9

What do we use that can fix attenuation?

TGC

10

What does TGC stand for?

Time gain compensation

11

Whats another word for TGC?

DGC

12

What does DGC stand for?

Depth gain compensation

13

What does the TGC slope provide?

Amplification of specific field echoes

14

What does TGC do?

It amplifies the far field to promote uniform in tissues
- eg) liver

15

What does it mean when your TGC is straight on the ultrasound machine?

You are getting equal amounts of amplification

16

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

17

What is the formula for attenuation in soft tissues?

a = 1/2f x L
a = attenuation
f = frequency
L = length/distance/thickness

18

How does attenuation occur in soft tissues?

0.5 there and 0.5 back = 1
- dB/cm x MHz
- compensates for both directions

19

What 2 things does overall gain do?

1. Amplification of entire field of view
2. Amplification of all incoming echo voltages

20

What is attenuation's unit?

Decible
- dB

21

How much is 3db? (2)

1. 1/2x
2. 2x

22

How much is 10dB? (2)

1. 1/10x
2. 10x

23

Define decible

The ratio between 2 intensities

24

What is the formula for attenuation in normal tissue?

a = ac x L
a = attenuation
ac = attenuation coefficient
L = length/distance

25

What is the formula for attenuation coefficient?

ac = 1/2f
ac = attenuation coefficient
f = frequency

26

Half value layer

The thickness of material that will halve the original intensity
- the distance it takes to drop 3dB