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SPI > Ch 7 Range Equation & Ch 8 Transducer Basics > Flashcards

Ch 7 Range Equation & Ch 8 Transducer Basics Flashcards

1
Q

What is time of flight also called?

A

go-return-time

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2
Q

What is time of flight?

A

Elapsed time from pulse creation to pulse reception

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3
Q

How is time of flight related to depth?

A

Directly, shallow imaging = shorter ToF, deep imaging = longer ToF

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4
Q

How do you calculate depth from go-return time?

A

1.54 (mm/us) x go-return time (us) / 2

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5
Q

When does the 13 microsecond rule apply?

A

Whenever sound is traveling through soft tissue

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6
Q

What is the 13 microsecond rule?

A

For every 13 us of go-return-time, the object creating the reflection is 1 cm deeper into the body

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7
Q

If GRT is 26 us, how deep is the structure creating the reflection?

A

2 cm deep

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8
Q

If GRT is 26 us, what is the total distance traveled by the pulse?

A

4 cm

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9
Q

How is PRP related to go-return time?

A

PRP is the go-return time of a sound pulse between the transducer and the bottom of the image

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10
Q

How is PRP related to depth?

A

Directly related

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11
Q

If depth is 10 cm, how long is the PRP?

A

130 us

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12
Q

If depth is 5 cm what is PRP?

A

5 x 13 = 65 us

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13
Q

How far can sound travel in 1 second?

A

To & from a depth of 77,000 cm, or to & from a depth of 7.7 cm 10,000 times

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14
Q

How is PRF related to depth?

A

Inversely

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15
Q

When depth is shallow, PRF is

A

High (can travel to & from depth more times/sec)

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16
Q

When depth is deep, PRF is

A

Low (to & from depth less time/sec)

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17
Q

How is PRF calculated using depth?

A

PRF = 77,000 (cm/s) / depth (cm)

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18
Q

What is a transducer?

A

Any device that converts one form of energy to another

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19
Q

How does an US machine convert energy?

A

Electrical to acoustic

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20
Q

What are the two functions of transducers?

A

Transmission and reception

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21
Q

What is transmission?

A

Electrical energy from the system is converted to sound

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22
Q

What is reception?

A

Reflected sound pulse is converted into electricity

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23
Q

What is the piezoelectric effect?

A

The property of certain materials to create voltage when they are mechanically deformed or when pressure is applied to them

24
Q

What is reverse piezoelectric effect?

A

Materials change shape when voltage is applied

25
Q

What are piezoelectric materials AKA?

A

Ferroelectric materials

26
Q

What are piezoelectric materials?

A

Materials which convert sound into electricity and vice versa

27
Q

How are piezoelectric materials sourced?

A

Some are natural ex. Quartz, tourmaline, in US mostly synthetic

28
Q

What is a common synthetic piezoelectric material used in US?

A

Lead zirconate titanate (PZT)

29
Q

What are the 7 components of a basic transducer?

A
  • case
  • electrical shield
  • acoustic insulator
  • PZT/active element
  • wire
  • matching layer
  • backing layer
30
Q

What does the transducer case do?

A
  • protects the internal components of the transducer from damage
  • insulates the patient from electrical shock
31
Q

What is the electrical shield?

A

Thin metallic barrier lining inside of case
- prevents electrical signals in the air from contaminating clinically important signals

32
Q

What is the acoustic insulator?

A

Cork or rubber layer, isolates internal components from case and prevent vibrations in the case from inducing electrical voltage in PZT

33
Q

What results in reflections at boundaries?

A

Differences in impedance

34
Q

The impedance of PZT compared to impedance of skin is

A

20 times greater

35
Q

If sound traveled directly from the PZT to skin what would happen?

A

Majority of sound would reflect back into PZT, only a small fraction would transmit, resulting in extremely limited clinical imaging

36
Q

What does the matching layer do?

A

It provides an impedance in between the active element and skin

37
Q

How does the matching layer affect reflections?

A

decreases reflection at the boundary of PZT and skin, increases transmission

38
Q

What does gel do?

A

Provides an impedance in between the matching layer and skin, “coupling” transducer to patient

39
Q

Order in decreasing order of impedance:
Gel, matching layer, PZT, skin

A

PZT > matching layer > gel > skin

40
Q

How thick is the matching layer?

A

1/4 wavelength thick

41
Q

How thick is the active element?

A

1/2 wavelength thick

42
Q

What is backing material AKA? What does it do?

A

Damping material, keeps pulses short

43
Q

What would happen without backing material?

A

PZT will vibrate longer than it should

44
Q

If the PZT vibrates for too long how does it affect the image?

A

Pulse has increased length and duration, image has lower resolution and accuracy

45
Q

What are the characteristics of damping material?

A
  • high degree of sound absorption
  • acoustic impedance similar to PZT
46
Q

Why does the backing material need to have similar impedance to PZT?

A

Sound pulse moves from PZT into backing material where it is absorbed

47
Q

What are three consequences of using backing material?

A
  1. Decreased sensitivity
  2. Wide bandwidth
  3. Low quality factor
48
Q

Why does backing material cause decreased sensitivity?

A
  • reduces PZT vibration during transmission and reception
  • makes transducers less responsive to small sound reflections returning from body
49
Q

What is bandwidth?

A

Range of frequencies in the pulse

50
Q

How does backing material create wide bandwidth?

A

PZT is restricted from vibrating freely, short duration sound click is released containing sound at many different frequencies

51
Q

What kind of bandwidth do continuous wave transducers produce?

A

Narrow bandwidth due to lack of backing material

52
Q

If a transducer with a 3 MHz frequency produces a pulse ranging from 1-5 MHz, what is the bandwidth?

A

5-1 = 4 MHz

53
Q

Long duration events are ________ bandwidth, short duration events are _______ bandwidth.

A

Narrow, wide

54
Q

What is quality factor?

A

A unitless number inversely related to bandwidth

55
Q

How is quality factor calculated?

A

QF = main frequency / bandwidth

56
Q

Why does backing material cause low quality factor?

A

Backing material causes wide bandwidth which results in low QF

57
Q

Which probes have a low Q factor? Which probes have high Q factor?

A

Wide bandwidth, narrow bandwidth

SPI (9 decks)

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