Chapters 12-13 Flashcards Preview

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Flashcards in Chapters 12-13 Deck (86):
1

Define mechanical transducer

contains a single, circular, disc-shaped active element that is physically moved

2

How many active elements/crystals are in mechanical transducers?

one

3

What is the image shape for a mechanical transducer?

fan or sector shaped

4

How is the scan plane of a mechanical transducer created?

through mechanical steering

5

Mechanical transducer have a ___ focal depth

fixed

6

Other terms used for fixed focal depth?

conventional, mechanical, or fixed focusing

7

What are two methods of fixed focusing?

internal-curved active element
external-with an acoustic lens

8

What happens with the PZT crystal is damaged in a mechanical transducer?

since they only have one single crystal; the entire image is lost when the crystal malfunctions

9

What type of transducers contain multiply active elements?

array

10

What is the arrangement of active elements in a linear array transducer?

active elements are arranged in a straight line

11

What is the arrangement of active elements in a annular array transducer?

elements are arranged as circular rings with a common center

12

What is the arrangement of active elements in a convex array transducer?

active elements are arranged in a bowed or arched line. the transducer may also be called a curve

13

When the beam is steered and focused using an electrical technique what is this called?

phasing

14

What is the image shape of a linear phased array?

fan or sector shaped

15

What is the beam steering in a linear phased array?

electronic steering process called phasing

16

How is the beam focused with a linear phased array?

focused electronically

17

What is the main advantage of phased arrays?

the electronically controlled, adjustable focusing

18

What happens to the PZT crystal in a damage phased transducer?

results in inconsistent or erratic beam steering and focusing

19

When is the sound beam steered?

if the spike line has a slope

20

What happens when a spike pattern is a straight line?

an unfocused sound beam is created

21

When is the the sound beam focused in a linear phased array?

the sound beam is focused if tge spike pattern is curved

22

In a linear phased array, the electronic pattern is a slope, what happens to the beam?

it is steered

23

In a linear phased array, the electronic pattern is a curvature, What happens to the sound beam?

transmit focusing

24

What shape crystals do annular phased arrays have?

bulls eye target/ disc shaped

25

How is beam steering achieved with annular phased arrays?

mechanical steering

26

What is the primary advantage with annular phased arrays?

multiply transmit focal zones

27

Smaller diameter PZT crystals create a ___focus beam

shallower

28

Larger diameter crystals create ___focus beams

deeper

29

What is the image shape for a annular array transducer?

fan or sector shaped

30

What happens when there is damage to a PZT crystal for an annular array transducer?

a horizontal or side to side band of dropout

31

What the linear sequential array have a small or large footprint?

large

32

What is the beam steering for linear sequential arrays?

a small group of the crystals are fired simultaneously

33

How is beam focusing achieved in a linear seq array?

electronic transmit focusing

34

How is receive focusing achieved in a linear seq array?

dynamically by introducing electrical delays in the signal returning from the transducer

35

What is the image shape for a linear seq array?

rectangular image

36

What happens if damage happens to a linear seq array?

if damage is done, then the portion of the image extending directly below the damage element is affected

37

Can linear sequential array transducer steer the sound beams electronically?

yes and this creates parallelogram shaped images

38

What shape do curved transducers have?

a bowed or curved shape

39

What is the beam steering for a convex seq array?

some, but not all the crystals are fired simultaneously to create each sound beam

40

How is focused achieved in a convex seq array?

electronically

41

How is transmit focusing achieved in a convex array?

by exciting the active elements in the fired group with a curved spike line pattern

42

How is dynamic receive focusing achieved in a convex array?

by introducing varying phase delays in the signal returning from the transducer to the US system during echo reception

43

What is the image shape for a convex array?

blunted sector shaped

44

What are vector arrays?

a combo of linear seques and linear phased arrays

45

what is the beam steering for vector arrays?

combo of linear and phased array so some but not all the crystals are fired sim to create a single sound beam

46

What is the beam focusing for vector arrays?

electronic focusing

47

What is the image shape for vector arrays?

trapezoidal shape

48

What shape of the active element creates the best elevational resolution?

active elements that are disc shaped (mechanical and annular phased array) provide thinnest slices

49

What is another term for slice thickness

elevational resolution

50

What transducers create thinner beams with improved slice thickness?

1.5 D array which have multiply crystals in the up and down direction

51

What array creates a 3D image?

2-D arrays

52

What does rendering do?

it creates an image from 3D data acquired during the US exam

53

Define side lobes

sound beams created by single element transducers are hour glass shaped. these off axis sound beams are side lobes

54

What do side lobes do?

reflections arising form within the side lobes degrade lateral resolution

55

What transducers create grating lobes?

array

56

What do grating lobes do?

degrade lateral resolution, reduce image quality, and create artifacts

57

Define apodization

reducing the strength of side and grating lobes

58

What are some methods to reduce grating lobes?

apodization and
subdicing- in a linear array transducer

59

Define dynamic aperture

is used to make a sound beam narrow over a greater range of depth and this optimizing lateral resolution

60

What resolution is improved with dynamic aperture?

lateral

61

In a linear phased array, what is the firing pattern that steers a beam to the left or right?

electronic slope

62

In a linear phased array, what is the firing pattern that focuses a sound beam?

electronic curvature

63

A machine that displays Doppler and 2D images is called?

duplex scanner

64

Images that were displayed one frame at a time where called?

static scanning

65

Define frame rate

ability to create numerous frames each second

66

What is frame rate determined by?

sounds speed in the medium
the depth of imaging

67

What are the units for frame rate?

hertz

68

Define temporal resolution

the ability to precisely position moving structures from instant to instant

69

Is temporal resolution better with higher or lower frame rate?

higher

70

What is temporal resolution determined by?

frame rate

71

What are units for temporal resolution?

hertz

72

What is the relationship between frame rate and time required to make a single image?

inversely and they are reciprocals

73

What are the system setting that affect frame rate?

imaging depth
number of pulsed per frame

74

What is the relationship between imaging depth and frame rate?

inversely

75

What is the formula for T frame?

=#pulses x PRP

76

how are pulses per frame and frame rate related?

inversely

77

What factors affect the number of pulses per frame?

number of pulses per scan line (multi-focus vs single focus)
sector size
liner per angle of sector (line density)

78

Multi focusing improves or degrades temporal resolution?

degrades

79

What improves with multi focusing?

lateral resolution

80

Another name for sector size?

field of view

81

Which is better a narrow sector or a wide sector for temporal resolution?

narrow sector

82

Which is better low line density or high?

low

83

What is the main advantage of high line density?

improved spatial resolution

84

What are the systems two major functions?

1. the preparation and transmission of electrical signal to the transducer, which creates a sound beam
2. the reception of electrical signals from the transducer, with subsequent processing into clinically meaningful images and sounds

85

What does the pulser determine?

the amplitude, PRP and PRF.

86

What does the beam former determine?

the firing delay patterns for phased array systems