Chapter 8-11 Flashcards Preview

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Flashcards in Chapter 8-11 Deck (97):
1

What is a transducer?

any device that converts one form of energy into another

2

What are two functions of ultrasound transducers?

-during transmission, electrical energy from the system is converted into sound
-during reception, the reflected sound pulse is converted into electricity.

3

What is the piezoelectric effect?

describes the property of certain materials to create a voltage when they are mechanically deformed or when pressure is applied to them.

4

What are some synonyms for PZT?

ceramic, active element or crystal

5

What is the commonly used material in transducers?

lead zirconate titanate (PZT)

6

What is it called when piezoelectric material change shape when a voltage is applied to them?

reverse piezoelectric effect

7

What is it called when materials convert sound into electricity and vice versa?

piezoelectric or ferroelectric

8

How thick is the PZT/ active element?

=1/2 wavelength

9

How thick is the matching layer?

=1/4 wavelength

10

What is the purpose of the matching layer?

increases the efficient of sound energy transfer between the active element and the body and protects the active element

11

What is the decreasing order of impedance?

PZT> matching layer>gel> skin

12

What are the consequences of using a backing material?

-decreased sensitivity
-wide bandwidth
-low quality factor

13

Define bandwidth

the range of frequencies in the pulse

14

Long duration events have a _____ bandwidth

narrow

15

Short duration events have a _____ bandwidth

wide or broadband

16

How are quality factor and bandwidth related?

inverse

17

What is the formula for quality factor?

=main freq/bandwidth

18

How is Q factor and pulse length related?

directly

19

Imaging probes are referred to as ____ Q?

low-Q

20

What transducer do not contain a backing material?

therapeutic transducer and CW so they have a narrow bandwidth and high-Q

21

Define polarization

exposing material to a strong electrical field while being heated to a substantial temperature

22

What is the temperature that the PZT is polarized?

curie temp or curie point

23

What is it called when piezoelectric properties are lost?

depolarization or depolarized

24

What is the difference between sterilization and disinfection?

sterilization is the destruction of all microorganism by exposure to extreme heat, chemical agents, and radiation
disinfection is the application of a chemical agent to reduce or eliminate infectious organism on an object.

25

How is pulse length related to pulse duration?

directly

26

How is pulse duration and bandwidth related?

inversely

27

What characteristics of the active element determine the frequency of sound created by a pulsed wave transducer?

1. the speed of sound in the PZT
2. thickness of the PZT

28

How is the speed of sound in PZT and frequency of sound related?

directly

29

How is frequency and PZT thickness related?

inversely

30

What is the range of thickness of PZT in diagnostic imaging?

0.2-1 mm

31

What is the formula for frequency in PZT?

freq (MHz)=speed in PZT/2xthickness

32

Define focus

the location where the beam is the narrowest
=1/2beam diameter

33

Another name for the near field

Fresnel zone or near zone

34

Define the near field

the region from the transducer to the focus

35

define focal length

also called focal depth and near zone length
the distance from the transducer to the focus

36

What other words can be used to describe focus?

focal point, the end of the near zone, the beginning of the far zone, or the middle of the focal zone

37

Another name for the far field

Far zone or fraunhofer zone

38

Define the far zone

the region that starts at the focus and extends deeper where the beam diverges or spreads out

39

What is the beam diameter at the transducer?

beam diameter = transducer diameter

40

What is the beam diameter at the focus?

beam diameter= 1/2 transducer element

41

What is the beam diameter at 2 NZL?

beam diameter=the transducer diameter

42

What is the beam diameter at deeper than 2 near zone lengths?

beam diameter is wider than transducer diameter

43

What are adjustable focus systems called?

phased array

44

What characteristics of a fixed focus transducer determine the focal depth?

1. transducer diameter
2. frequency of the sound

45

How are transducer diameter and focal depth related

directly

46

how are frequency and focal depth related?

directly

47

What happens at a shallow focus?

smaller diameter PZT and lower freq

48

What happens at a deep focus?

larger diameter PZT and higher freq

49

Higher freq sound creates a _____ focus

deeper

50

What is beam divergence?

the gradual spread of the ultrasound beam in the far field

51

What two factors combine to determine beam divergence?

1. transducer diameter
2. frequency of the sound

52

How are crystal diameter and beam divergence related?

inversely

53

What do larger diameter crystals improve in the far field?

lateral resolution

54

How is frequency and beam divergence related?

inversely

55

What do high frequency sound beams improve?

lateral resolution

56

What happens with less divergence?

larger diameter, and higher freq

57

What happens with more divergence?

small diameter, and lower freq

58

What are other names for V-shaped waves?

spherical waves, diffraction patterns, and Huygens wavelets

59

What explains why a sound beam created by a disc shaped crystal is hourglass shaped?

Huygens principle

60

What is the ability to create accurate images?

resolution

61

Define axial resolution

deals with structures that are parallel to the sound beam
front to back
units: mm
distance

62

How are SPL and axial resolution related?

directly

63

What is axial resolution related to?

SPL and pulse duration

64

What are synonyms for axial resolution?

LARRD
longitudinal
axial
radial
range
depth

65

Is axial resolution adjustable?

no

66

True or false: shorter pulses improve image quality and axial resolution

true

67

true or false: you can a lower numerical number for axial resolution in order for it to be considered better image quality

true

68

what is the formula for axial resolution?

SPL/2

69

How is a short pulse created?

1. less ringing-damping
2. higher frequency

70

Define lateral resolution

side by side or perpendicular to the sound beam main axis
units of distance

71

What is lateral resolution determined by?

the beam width/ diameter
lateral resolution=beam diameter

72

What does lateral resolution vary with?

beam diameter varies with depth so so does lateral resolution

73

what are synonyms for lateral resolution?

LATA
lateral
angular
transverse
azimuthal

74

Where is the best lateral resolution?

at the focus
and lateral resolution is good at the focal zone

75

What resolution is better for imaging?

axial

76

What is lateral resolution best with?

narrowest beam

77

Does axial resolution change with depth? lateral?

axial-no
lateral- yes

78

What are the methods of focusing?

external- with a lens
internal -with a curved element
phased array- with the electronic of the US system

79

What is fixed focusing?

mechanical focusing/conventional and includes both internal and external and the focal depth and extent of focusing can not be changed

80

What word is used to described adjustable or multiple focusing?

phased array

81

What are four distinct modification that a sound beam undergoes when focused?

1. the beam diameter in the near field and focal zone narrows (becomes smaller)
2. the focus moves closer to the transducer (NZL is reduced)
3. the beam diameter beyond the focal zone widens (lateral resolution improves in the near zone and focus and degrades in the far zone)
4. the size of the focal zone is reduced

82

What is freq of CW determined by?

freq of electrical signal from US system

83

What is freq of pulsed wave determined by?

thickness of ceramic and speed of sound in ceramic

84

What is the focal length determined by?

diameter of ceramic and freq of sound

85

What is the beam divergence determined by?

diameter of ceramic and freq of sound

86

What are the three display modes?

Amplitude, motion and brightness

87

How does A mode appear?

as a series of upward spikes
a big city skyline

88

What does the x axis of A mode represent?

depth

89

What does the y axis of A mode represent?

amplitude

90

Where is A mode used?

ophthalmology

91

What does the x axis of B mode represent?

depth

92

what does the z axis of B mode represent?

amplitude

93

What does the brightness of the dots on B mode represent?

the strength of the reflection

94

What does the x axis of M mode represent?

time

95

What does the y axis of M mode represent?

depth

96

What display mode provides info regarding reflector motion with respect to time?

M mode

97

What mode provide the foundation for real-time gray scale imaging?

B mode