Lesson 4 (Part 1) Flashcards Preview

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Flashcards in Lesson 4 (Part 1) Deck (28)
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1
Q

What does the reception channel of the beam former do?

A

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

2
Q

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

A

Digital signals

3
Q

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

A
  1. Filtering
  2. Detection
  3. Compression
4
Q

What does pulsed wave US produce?

A

A bandwidth of transmitted frequencies

5
Q

What is the strongest frequency?

A

Fundamental frequency

6
Q

Bandwidth

A

Range of frequencies contained in a pulse

7
Q

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

A

Long SPL

8
Q

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

A

Short SPL

9
Q

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

A

Wider

- shorter SPL

10
Q

What does filtering do?

A

Gets rid of frequencies we do not want

11
Q

How does filtering work? (3)

A
  1. Select the desired frequency for the bandwidth
  2. Pass a range of frequencies through it
  3. Rejects those above and below the bandwidth
12
Q

What kind of filters does the signal processor use?

A

Bandpass filters

13
Q

When might we adjust a filter?

A

When dealing with harmonics

14
Q

Bandpass filter

A

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

15
Q

What are tuned amplifiers used for?

A

To reduce noise

16
Q

Why does the bandwidth decrease while the echoes return?

A

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

17
Q

What does an input filter include? (2)

A
  1. Echo signal bandwidth

2. Electronic noise with unlimited bandwidth

18
Q

What is a filter bandwidth designed to accommodate?

A

A single bandwidth

19
Q

Harmonics

A

Modification of the sinusoidal waveform as it propagates through the tissue

20
Q

How do harmonics work?

A

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

21
Q

What is the first harmonic sent out called?

A

The fundamental frequency

22
Q

What does the 2nd harmonic being set out do?

A

Produces echoes that will allow for better resolution

23
Q

What function do filters perform in signal processors?

A

Harmonics

24
Q

What happens when we press the THI button?

A

The fundamental frequency is filtered out

25
Q

What are the benefits for harmonics? (4)

A
  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
26
Q

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

A

Better lateral resolution

27
Q

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

A

Better elevational resolution

28
Q

How are side lobes/grating lobes eliminated with harmonics?

A

Because they are not strong enough to generate harmonics