Lesson 4 (Part 1)

Question 1

What does the reception channel of the beam former do?

Answer 1

Amplifies and combines the echo voltages from individual elements and sends them to signal processor

Question 2

When we are with the signal processor what kind of signals are we dealing with?

Answer 2

Digital signals

Question 3

What are the functions of the signal processor? (3)

Answer 3

1. Filtering
2. Detection
3. Compression

Question 4

What does pulsed wave US produce?

Answer 4

A bandwidth of transmitted frequencies

Question 5

What is the strongest frequency?

Answer 5

Fundamental frequency

Question 6

Bandwidth

Answer 6

Range of frequencies contained in a pulse

Question 7

What kind of SPL do you have with a narrow bandwidth?

Answer 7

Long SPL

Question 8

What kind of SPL do you have with a wide bandwidth?

Answer 8

Short SPL

Question 9

Which length of bandwidth will give you a better axial resolution?

Answer 9

Wider

- shorter SPL

Question 10

What does filtering do?

Answer 10

Gets rid of frequencies we do not want

Question 11

How does filtering work? (3)

Answer 11

1. Select the desired frequency for the bandwidth
2. Pass a range of frequencies through it
3. Rejects those above and below the bandwidth

Question 12

What kind of filters does the signal processor use?

Answer 12

Bandpass filters

Question 13

When might we adjust a filter?

Answer 13

When dealing with harmonics

Question 14

Bandpass filter

Answer 14

A filter that passes a range of frequencies and rejects those above or below the acceptance bandwidth

Question 15

What are tuned amplifiers used for?

Answer 15

To reduce noise

Question 16

Why does the bandwidth decrease while the echoes return?

Answer 16

Because the higher frequencies in the bandwidth are more attenuated compared to the lower ones

Question 17

What does an input filter include? (2)

Answer 17

1. Echo signal bandwidth

2. Electronic noise with unlimited bandwidth

Question 18

What is a filter bandwidth designed to accommodate?

Answer 18

A single bandwidth

Question 19

Harmonics

Answer 19

Modification of the sinusoidal waveform as it propagates through the tissue

Question 20

How do harmonics work?

Answer 20

Multiple frequencies are produced by fundamental frequency (fₒ)
- odd and even multiples of fₒ

Question 21

What is the first harmonic sent out called?

Answer 21

The fundamental frequency

Question 22

What does the 2nd harmonic being set out do?

Answer 22

Produces echoes that will allow for better resolution

Question 23

What function do filters perform in signal processors?

Answer 23

Harmonics

Question 24

What happens when we press the THI button?

Answer 24

The fundamental frequency is filtered out

Question 25

What are the benefits for harmonics? (4)

Answer 25

1. Narrower beam width
2. Narrower in the z plane / thinner beam
3. Side lobes/Grating lobes (artifacts) are eliminated
4. Reduction of anterior reverberation
   - harmonics beam is generated further into tissue

Question 26

What kind of resolution do you get with a narrower beam width?

Answer 26

Better lateral resolution

Question 27

What kind of resolution do you get with a narrower in the z plane / thinner beam width?

Answer 27

Better elevational resolution

Question 28

How are side lobes/grating lobes eliminated with harmonics?

Answer 28

Because they are not strong enough to generate harmonics