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Physics 2 > Lesson 4 (Part 2) > Flashcards

Lesson 4 (Part 2) Flashcards

1
Q

Where are harmonics generated?

A

In the tissue

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2
Q

What is an example of an aftifact?

A

Anterior Reverberation

- main bang

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3
Q

Anterior Reverberation

A

Reflections between the transducer face and skin surface cause multiple horizontal lines of echoes to appear in the near field
- can also occur at the ribs

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4
Q

What are some drawback of harmonics? (3)

A
  1. Decreased penetration
  2. Worse Axial Resolution
  3. Narrower bandwidths
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5
Q

Why is decreased penetration a draw back with harmonics?

A

Higher frequency means more attenuation

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6
Q

Why does axial resolution weaken with harmonics?

A

Because the transducer must fit in the bandwidths of both the fo and 2fo, therefore, the bandwidth on each will be small
- compared to the overall bandwidth of the transducer

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7
Q

What does it mean if you have a narrower bandwidth? (3)

A
  1. Longer SPL
  2. Larger (worse) axial resolution
  3. Worse resolution
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8
Q

How can you solve the problems associated with narrower bandwidths?

A

Pulse Inversion Harmonic Imaging

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9
Q

Pulse Inversion Harmonic Imaging

A

2 pulses are sent out back to back, one at a regular pulse and the other at a inverted pulse

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10
Q

Where are harmonic signals produced in?

A

Tissues

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11
Q

What happens to the echo of the fundamental signal?

A

Destructive interface

- they will cancel each other out and end up with no signal

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12
Q

What happens to the echo of the harmonic signal?

A

Non sinusoid, meaning when combined they wont cancel each other out harmonic signal will be preserved

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13
Q

What does wider bandwidth allow for? (3)

A
  1. Shorter SPL
  2. Smaller (better) axial resolution
  3. Better resolution
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14
Q

What happens to the frame rate with sending out multiple pulses?

A

It decreases

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15
Q

What is another word for detection?

A

Demodulation

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16
Q

Detection

A

Is the conversion of echo voltages from radio frequency form to amplitude form

17
Q

Compression

A

The process of decreasing the differences between the smallest and the largest echo amplitudes to a usable range

18
Q

What function does compression perform?

A

Dynamic range

19
Q

Dynamic range

A

The power ratio of the largest to smallest amplitude that a system can handle
- relationships between the weakest and the strongest echos expressed in decibles

20
Q

What is the units for dynamic range?

A

Decibles

- dB

21
Q

What is the formula for power ratio?

A

Voltage ratio^2

22
Q

What does 60dB dynamic range mean?

A

That the strongest echo is 10^6 times stronger than the weakest echo

23
Q

What is the dynamic range for amplifiers?

A

100-170dB

24
Q

What is the dynamic range for displays?

A

30dB

25
Q

What is the dynamic range for human vision?

A

20dB

26
Q

What do greater values indicate?

A

The ability to detect weaker echoes

- greater sensitivity

27
Q

What can the larges power approximately be?

A

100x the smallest

- for our viewing of the display

28
Q

What do amplifiers amplify?

A

The weaker signals compared to the larger ones

29
Q

How is compression adjusted?

A

It is operator dependent

30
Q

What does controlling the compression allow for?

A

The reduction of dynamic range by assigning some weak echo amplitude values to zero or by assigning some of the strongest to max

31
Q

How does compression reduce dynamic range?

A

With selective amplification

- contributes with contrast resolution

32
Q

Contrast resolution

A

Being able to separate two different echoes as two different shades of gray

33
Q

What does compression affect?

A

Our contrast

34
Q

What happens when you decrease dynamic range? (2)

A
  1. More contrast

2. Grainier image

35
Q

What happens when you increase dynamic range? (2)

A
  1. Less contrast

2. Smoother image

Physics 2 (10 decks)

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