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Ultrasound Physics > Quiz 3 > Flashcards

Quiz 3 Flashcards

(69 cards)

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1
Q

How does an ultrasound machine measure distances?

A

By measuring the time of flight (go-return time)

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2
Q

What is the time of flight (go return time)?

A

The system measuring the time the pulse starts to pulse reception

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3
Q

What is range equation?

A

Depth(mm) = 1.54 X go-return time(us) divided by 2

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4
Q

What is the 13 us rule?

A

For every 1 cm in depth a reflector is at, the go return time is 13us

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5
Q

What is the length of a pulse for time of fight for a shallow reflector?

A

Short

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6
Q

What is the length of a pulse for time of fight for a deep reflector?

A

Long

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7
Q

What is the term used to describe the distance between the transducer and the depth of image?

A

Go return time
(time of flight)

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8
Q

When depth is deep, PRP is?
When depth is shallow, PRP is?

A

Long
Short

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9
Q

What is the formula for PRP and go return time?

A

PRP(us) = imaging depth(cm) X 13(us/cm)

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10
Q

What is the relationship between PRF and Depth?

A

Inversely related

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11
Q

If the depth is shallow, the PRF will be? (High or low)

A

High

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12
Q

If the depth is deep, the PRF will be? (High or low)

A

Low

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13
Q

What is the formula for PRF and depth?

A

PRF = 77,000cm/s divided by imaging depth (cm)

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14
Q

What does an ultrasound transducer do?

A

Converts energy from one form to another

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15
Q

Transmission = ?

A

Electrical to sound

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16
Q

Reception = ?

A

Sound to electrical

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17
Q

What are piezoelectric materials?

A

Materials that convert electric energy to sound energy and sound energy to electrical energy

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18
Q

What are examples of natural piezoelectric materials?

A

Quartz and Tourmaline

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19
Q

What is the name of the synthetic piezoelectric material?

A

PZT (lead zirconate titanate)

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20
Q

What is the piezoelectric effect?

A

The ability of certain materials to make an electric charge in response to a mechanical pressure

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21
Q

What is the matching layer?

A

The layer between the skin and the PZT

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22
Q

What is the importance of ultrasound gel?

A

Acts of a coupling agent to create clearer images

Has a similar importance to skin

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23
Q

What is the impedance of the matching layer in decreasing order?

A

PZT > matching layer > gel > skin

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24
Q

What is the purpose of the backing material?

A

Helps to improve axial resolution due to shorter pulses

Dampens the ringing

Shorter pulse = better resolution

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25
What is the purpose of the damper in the backing layer?
Highly sound absorbent to reduce ringing and improve image quality
26
What are the 3 ways backing material affects sound waves?
-decreased sensitivity to weak reflected echos -wide bandwidth -low quality factor
27
What is the difference between the highest and lowest frequency emitted called?
Bandwidth
28
How is quality factor related to bandwidth?
Inversely related
29
What do non-imaging probes consist of?
Narrow bandwidths High Q factor Long CW - long pulses No backing material Increased sensitivity
30
What do imaging probes consist of?
Improved axial resolution Low QF Reduced sensitivity Uses backing material Created short pulse lengths
31
What determines the frequency of sound in pulsed wave probes?
Speed of sound in PZT Thickness of PZT
32
What determines the frequency of sound in CW probes?
The frequency of sound emitted by the CW probe = the frequency of electrical signal Continuous voltage of the frequency is used
33
How is speed of sound in PZT related to frequency?
Directly related
34
What is the relationship of the PZT thickness and frequency?
Inversely related Thin PZT = High frequency Thick PZT = low frequency
35
What is the formula for PZT thickness?
Frequency(MHz)=sound speed in PZT(mm/us) divided by 2 X thickness (mm)
36
What are the 5 parts of the sound beam?
Focus Near zone Focal length (near zone length) Far zone Focal zone
37
What is the focus?
Narrowest part of the beam The width is 1/2 as wide as it exits the transducer
38
What is the Near zone?
Area between the transducer and focus 1 distance of 1 NZL is 1/2 the crystal diameter Determined by frequency and crystal / diameter
39
What are other names for the Near zone?
Fresnel zone Near field
40
If the diameter decreases, what happens to the near zone length?
Decreases
41
What are other names for focal length?
Focal depth Near zone length
42
What is the focal length?
Distance from transducer to the focus
43
What are other names for the Far zone?
Far field Fraunhofer
44
What is the far zone?
Area from focus that extends deeper (spreads out wider) Beginning of far zone is 1/2 as wide as transducer 2 near zone lengths from transducer , the beam is the same size as it was at the transducer
45
What is the focal zone?
Narrow region on either side of the focus Great image quality 1/2 in near field 1/2 in far field
46
At the transducer the beam diameter is?
Equals transducers diameter
47
At the focus the beam diameter is?
1/2 the transducers diameter
48
At 2 near zone lengths the beam diameter is?
Equals transducer diameter
49
The deeper than 2 near zone lengths beam diameter is?
Wider than the transducer diameter
50
What are other names for focal length?
Focal depth Near zone length
51
What determines focal depth?
Transducer diameter Frequency of sound
52
What is the relationship between the transducer diameter and focal depth?
Directly related Large diameter = deep focal depth Small diameter = shallow focal depth
53
What is the relationship between the transducer frequency and focal depth?
Directly related Increased frequency = increased focal depth Decreased frequency = decreased focal depth
54
What is beam divergence?
Gradual spreading out of the beam in the far field
55
What is the beam divergence determined by?
Transducer diameter Frequency
56
How is PZT diameter related to beam divergence?
Inversely (Small diameter = increased divergence) (Large diameter = decreased divergence)
57
How is frequency related to beam divergence?
Inversely related (Low frequency = more spreading in far field) (High frequency = less spreading)
58
What is the relationship between propagation speed and frequency?
Directly related
59
What is the relationship between the thickness of PZT and frequency?
Indirectly related (Thick crystal = lower frequency) (Thin crystal = high frequency)
60
CW dopplers create what kind of bandwidth?
Narrow
61
US probes create what kind of bandwidth?
Wide
62
What is destructive interference?
Out of phase waves combine to form a single wave with less amplitude
63
What is constructive interference?
In phase waves combine to form a wave with greater amplitude
64
How thick is the active element(crystal)?
1/2 wavelength thick
65
How thick is the matching layer?
1/4 wavelength thick
66
How do you calculate CW operating frequencies?
CW frequency = electric frequencies being inputted
67
What is the near zone length determined by
Frequency Crystal diameter
68
How is NZL and frequency related?
Directly
69
What is the reverse piezoelectric effect?
When a materials changed shape because of an electrical charge

Ultrasound Physics (7 decks)

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