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Phys 254 > Physics Quiz 1 Review > Flashcards

Physics Quiz 1 Review Flashcards

1
Q

Which of the following transducer component is responsible for improving axial resolution?
1. The insulator ring
2. The matching layer
3. The damping material
4. The piezoelectric element

A

The damping material

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2
Q

Explain the method of probe excitation used in a modern day array probe?

A

Burst spike: AC voltage. We can send it at a different frequency beside resonant frequency.

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3
Q

Calculate the crystal thickness for a probe emitting sound with a period of 0.25 microseconds. The crystal in question has a sound velocity of 4000 m/s?

A

Crystal thickness = 1/2 lambda

T = 0.25 microseconds
C = 4000 m/s
lambda = C/F
F = 1/T
F = (1/0.25) = 4

Lambda = 4/ 4
Lambda = 1
Thickness = 1/Lambda
Thickness = 0.5 mm

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4
Q

How does the addition of damping material change the efficiency of the probe

A

It decreases the efficiency because the amplitude of the sound would be reduced.
We reduce the efficiency of the probe

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5
Q

Which of the following allows probe to multifunction in that they can obtain 2D images and doppler information?

A

Electric damping

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6
Q

Explain the -6dB bandwidth

A

The useable bandwidth. All of the frequencies that have 1/2 the centre frequency amplitude and 1/4 intensity of the resonant frequency.

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7
Q

Give me three reasons why firing a single crystal in an array probe is not desirable

A
  1. Smaller the source sound more divergence. Lateral resolution
  2. Beam steering
  3. Vary the focus
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8
Q

What is the transducer Q factor?

A
  1. Reciprocal of frequency bandwidth.
  2. Mechanical coefficient
  3. Energy stored/ energy lost
  4. The higher the Q the better the transmitter
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9
Q

How does the sector array probe steer the sound to achieve its field of view?

A

Crystals are fired nearly at the same time, beams diverge in the far field.
Delayed Firing

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10
Q

Increasing the damping will shorten the SPL and improve the axial resolution while widening the bandwidth and decreasing the Q factor T/F?

A

True

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11
Q

Which of the following probes is electronically steered and focused?

  1. Wobbler
  2. Annular array
  3. Linear translation
  4. Linear phased array
A

Linear phased array
annular array electronically focused but mechanically steered

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12
Q

When scanning the gallbladder, you have three single disc mechanical transducers to choose from. All are 5 MHz transducers and have the following diameter elements; 6 mm, 9mm and 11mm respectively. Which one would you choose?

A

The 6 mm probe
The gallbladder is a superficial structure and the 6 mm probe will have the nearest near zone length.

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13
Q

What determines the resonant frequency of the transducer.

A

The thickness of the crystal in the probe and what it is made of.

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14
Q

Which of the following is the best way to improve lateral resolution in the deeper aspects of an image using a single disc transducer?

  1. Increase the damping
  2. Add more matching layers
  3. Increase the crystal diameter
  4. Fire small segments of crystal sequentially
A

Increase the crystal diameter.
The narrower the beam, the better the lateral resolution, therefore if we use a crystal with a wider diameter we can have a narrow scanning zone deeper

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15
Q

Which of the following transducer would be best to quantify the hemodynamics significance of a stenosis in an artery?

  1. Low frequency and low Q
  2. Low frequency and high Q
  3. High frequency and low Q
  4. High frequency and high Q
A

Low frequency and high Q

Why? Firstly, we need to use doppler so we can determine the velocity in the arteries. Doppler pulses are longer therefore we can’t use a low Q probe. Using a higher frequency probe might not be able to pick up the blood flow. Therefore we need to use the Lower frequency probe

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16
Q

What does the housing do?

A

Keeps parts inside

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17
Q

What does the tuning coil do?

A

Helps to regulate the driving frequency

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18
Q

What does the electric shield do?

A

Prevents electrocution and reduces noise

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19
Q

What does the insulator do?

A

Limits radial mode vibration

20
Q

What does the backing material do?

A

Keeps the pulses short

21
Q

What does the element do?

A

Responsible for the P. Properties of the probe

22
Q

What does the matching layer do?

A

Improves the sensitivity of the probe

23
Q

Explain what type of energy an ultrasound probe converts?

A

Mechanical to electrical and vice versa

24
Q

How is the thickness of the piezoelectric element determined?

A

One half the wavelength for the desired frequency

25
Q

Name two modes of vibration that occur within a piezoelectric disc.

A

Radial and thickness

26
Q

Why are composite crystals often used over naturally occurring?

A

Cheaper and better transmission and reception

27
Q

What materials are used for damping?

A

Epoxy resin and tungsten powder

28
Q

Damping decreases the transducer efficiency so why is it used?

A

Shortens the pulse which improves axial resolution

29
Q

State what two modes can be used to drive transducers

A

Burst and spike

30
Q

How are synthetic materials given piezoelectric properties?

A

Heat to Currie temperature and place in an electrical field to polarize the dipoles

31
Q

State the range of curie temperatures?

32
Q

Describe the purpose of the matching layer

A

Improves sensitivity and reduces the reflection at the surface

33
Q

What is the impedance of the matching layer?

A

Between the crystal and skin

34
Q

Why is transducer bandwidth important in transducer design?

A

Relates to the length of the pulse and the quality of axial resolution. Also allows for multi-frequency probes

35
Q

Explain the difference between a shock-excited and burst excited transducer?

A

Shock is DX current where operating frequency is equal to resonant frequency and burst is AC current where driving frequency can be altered

36
Q

What is the frequency of a crystal that has a thickness of 0.385

37
Q

What is fractional bandwidth?

A

Bandwidth/ frequency

38
Q

What is the transducer Q?

A

Quality factor- energy stored/ energy lose

39
Q

How is transducer Q related to axial resolution and bandwidth?

A

Low Q = better axial resolution and wider bandwidth

40
Q

Explain which type of Q Factor is advisable for DI and which.

A

Lower for better axial resolution and wider bandwidth

41
Q

How is Q calculated>

A

Ratio of center frequency of bandwidth

42
Q

Which is better, a narrow or wide- band transducer?

A

Wide because of the shorter pulse and better resolution

43
Q

The Z value of the matching layer is considered in the transducer design, explain why?

A

Must be between the Z value of the crystal and skin

44
Q

Give two other names for resonance frequency

A
  1. Fundamental
  2. Natural
45
Q

How do you calculate matching layer?

A

1/4 lambda

Phys 254 (19 decks)

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