Lesson 17 (Part 1) Flashcards Preview

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Flashcards in Lesson 17 (Part 1) Deck (29)
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1

Linear phased array

Straight line of elements

2

How are linear phased array elements fired?

Voltage applied with a small difference

3

Phasing

Firing with a small time difference

4

How much time is delayed between firing of each element?

< 1 us

5

When is the delay bigger?

When the beam has a larger angle

6

What happens when the delay is straight with the beam?

There is no delay

7

Wavefront

Angled line that is created by the different phasing arrays

8

How does a wave always travel?

Perpendicular to its wavefront

9

What does the new wavelength created by secondary wavelets happen according to?

Huygen's principle

10

Huygen's principle

Every point on a wave-front may be considered a source of secondary spherical wavelets which spread out in the forward direction at the speed of light

11

How do we steer the beam when scanning the patient?

By phasing

12

If you want to steer the beam to the right how is phasing organized?

On a left slope

13

If you want to steer the beam to the left how is phasing organized?

On a right slope

14

Why do we change our focus?

To get a better resolution

15

What can we change at a particular spot?

Intensity

16

When is beam width smallest?

At the focus

17

Electronic focusing

Using phased array to focus the beam

18

What happens in electronic focusing when you have a greater curvature?

It places the focus closer to the transducer

19

What happens in electronic focusing when you have a lesser curvature?

It places the focus deeper
- farther away from them transducer

20

How can electronic focusing move?

Based on time delayed

21

What does increase delay of beams lead to?

Greater curvature
- focus is closer to the surface

22

How do we achieve curvature? (2)

1. Fire outside crystals first and so on
- 1 and 8, 2 and 7...
2. Fire the middle ones last

23

What does decrease in delay of beams lead to?

Lesser curvature
- farther focus

24

What does an unfocused sound beam have?

A natural focus

25

What is a focused sound beam the same as?

Electronic focusing

26

What does multiple foci require?

Multiple pulses
- each focused at a different depth

27

Montage

Overlaid images

28

What does montage lead to?

Better resolution at each depth

29

What happens when the frame rate decreases?

It lags