Lesson 3 (Part 2)

Question 1

What do longer paths have? (2)

Answer 1

1. Greater attenuation
2. Later arrival times
   - the later it arrives the more amplified it is

Question 2

What is an increase of gain with depth known as?

Answer 2

Time gain compensation slope

Question 3

What is the TGC slope measured in?

Answer 3

dB/cm x MHz

Question 4

What is the TGC slope for soft tissue?

Answer 4

1 dB/cm x MHz

- 0.5 dB/cm x MHz each way

Question 5

What is the max the TGC slope can be?

Answer 5

100dB

- 1x10^10 x

Question 6

What is lateral compensation used for?

Answer 6

Adjacent structures that have different attenuations

Question 7

What is the drawback for amplification?

Answer 7

It also amplifies noise

Question 8

What does the amplification of noise result in? (2)

Answer 8

1. Grainier signals

2. Weaker echos from the electric current

Question 9

What does attenuation depend on?

Answer 9

Frequency

Question 10

What does TGC compensate for?

Answer 10

The effect of attenuation on an image

Question 11

What determines max imaging depth? (2)

Answer 11

1. Attenuation

2. Max amplifier

Question 12

What is the max amplifier determined by?

Answer 12

Noise

Question 13

Why does the max amplifier determine imaging depth?

Answer 13

Because if it was turned up past too much then the noise would take over the screen and it would not be readable

Question 14

What happens to the echo voltages after amplification?

Answer 14

They are digitalized

Question 15

ADCs

Answer 15

Analog-to-digital converter

Question 16

Analog-to-digital converter

Answer 16

Convert the voltage from an analog to the digital form

- goes from voltage to numbers

Question 17

What does analog mean?

Answer 17

Proportional

Question 18

What does digital mean?

Answer 18

In the form of discrete numbers

- binary numbers

Question 19

What happens to the echo voltages after they get digitalized?

Answer 19

They are replaced by a series of numbers and further manipulation of the echoes is accomplished as digital signal processing
- they are digital delays now

Question 20

What does ADC do?

Answer 20

It interrogates the incoming voltages at the regular intervals

Question 21

What does ADC determine?

Answer 21

Its values at each interrogation instant

Question 22

What must the interrogation rate be?

Answer 22

Twice the highest frequency involved

Question 23

Why must the interrogation rate by twice the highest frequency involved?

Answer 23

In order to preserve the harmonics

Question 24

What happens to the echo voltages after digitizing?

Answer 24

The echo voltages pass through digital delay lines to accomplish reception dynamic focuses and steering functions

Question 25

What are echo delays the same as?

Answer 25

Pulse delays

- but they are digital delays

Question 26

What does echo delays allow? (2)

Answer 26

1. Focus

2. Steering

Question 27

What happens after echo delays?

Answer 27

The echo voltages are added together in the adder (summer) to produce the resulting scan line

Question 28

What does the summer (adder) do?

Answer 28

Produces the scan line

Question 29

What are 2 other components that are accomplished as part of the summing process?

Answer 29

1. Reception apodization

2. Dynamic aperture functions

Question 30

What is the beam former responsible for? (5)

Answer 30

1. Electronic beam scanning
2. Steering
3. Focusing
4. Apodization
5. Aperture functions with arrays