Lesson 2 (Part 2) Flashcards Preview

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Flashcards in Lesson 2 (Part 2) Deck (36)
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1
Q

What does the instrument automatically achieve?

A

The highest PRF

2
Q

Pen

A

Penetration

3
Q

Why must pen x PRF not exceed 77cm/ms?

A

In order to avoid echo misplacement

- pen(cm) x PRF (kHz) < 77(cm/ms)

4
Q

What happens to PRF if frequency is reduced and pen increases?

A

It gets reduced

-avoiding echo misplacement

5
Q

What happens if you go over 77cm/ms?

A

You get an artifact

- range ambiguity

6
Q

What happens to PRF in 2D if the depth is increased by 4x?

A

It decreases by 4x

7
Q

What gets produced by a greater voltage amplitude? (2)

A
  1. Greater amplitude pulse

2. Greater intensity pulse

8
Q

What does AMP(voltage) equal?

A

AMP(pulse)

9
Q

Amplitude

A

The power or strength of the beam entering the tissue

- closely related to intensity

10
Q

What do pulse delays do? (2)

A
  1. Decided how many element/crystals are involved

2. Which ones are getting fired

11
Q

What is pulse delays involved with? (6)

A
  1. Sequencing arrays
  2. Phasing
  3. Electronic focusing
  4. Dynamic aperture control
  5. Apodization
  6. Code excitation
12
Q

Sequencing array

A

Multiple blocks of sound, each producing a scan line

13
Q

Phasing

A

Microsecond delays between each element firing

14
Q

What does phasing help with?

A

Steering

15
Q

Electronic focusing

A

Microsecond delays between firing elements on a curved delay patter in order to send the sound beam into a focal point

16
Q

What does adjusting the delays do in electronic focussing?

A

It puts the focus either closer to or farther away

17
Q

What does the dynamic aperture decide?

A

The width of the aperture

18
Q

What can the dynamic aperture affect? (2)

A
  1. Our near zone length

2. Beam width

19
Q

How does the dynamic aperture affect our imaging?

A

Through lateral resolution

- LR = beam width

20
Q

What happens if you use a small aperture?

A

You will get a better picture

- higher resolution

21
Q

What does apodization do?

A

It decreases the strength to the outer elements

- reducting of grating lobes in arrays

22
Q

What does apodization only work for?

A

Arrays

- not side lobes

23
Q

What is the ensemble length?

A

1

24
Q

What is the doppler ensemble length?

A

3-30

- has some delays in between

25
Q

What does coded excitation involve?

A

A decoder in the beam former

26
Q

What does coded excitation not include?

A

Range ambiguity

27
Q

Why doesn’t coded excitation include range ambiguity?

A

Because the decoder knows how it is sent out

28
Q

What does coded excitation allow? (5)

A
  1. Multiple foci
  2. Spatial compounding
  3. Increased penetration
  4. Increased contrast resolution
  5. B-flow imaging
29
Q

B-flow imaging

A

Multiple pulses are sent down the same scan line and the decoder stacks the received echos
- constructive interference

30
Q

What do you get with B-flow imaging?

A

Overall higher intensity echoes

31
Q

Is B-flow and B-mode the same thing?

A

No

32
Q

Channel

A

Is an independent signal path consisting of a transducer element, delay and possibly other electronic components

33
Q

Transmission channel

A

Each path TO each individual element is a channel

- pulse –> pulse delays –> element

34
Q

Reception channels

A

Each path FROM each individual element is a channel

- element –> amplifier/ADC –> echo delays/summer

35
Q

What does an increased number of channels allow?

A

More precise control of beam characteristics

36
Q

What do numbers of channels not exceed?

A

The number of elements in the transducer