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What is the principle of Piezoelectricity?

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350 Terms

1

What is the principle of Piezoelectricity?

“Some materials, when deformed by an applied pressure, produce a voltage”

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2

What happens when a voltage is applied to a Piezoelectric element? What does this depend on?

  1. Thickness of element increases or decreases

  2. Depends on polarity of voltage

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3

What would happen if a synthetic Piezoelectric element was created and reheated to the Curie point?

Destroys all Piezoelectric properties

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4

What is the fo (operating freq) of a crystal determined by?

  1. Crystal

    1. Propogation speed

    2. Thickness

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5

Operating Frequency (fo) Formula

fo = cPZT / 2 * cth

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6

How are thickness and operating frequency related?

  1. Indirectly

    1. Thin elements = high freq

    2. Thick elements = low freq

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7

What is the sound beam a combination of?

All sound arising from different point-like sources (wavelets) on transducer crystal face

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8

What occurs due to the superposition of all sound waves in the beam?

Natural focusing (narrowing)

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9

How is the shape of the sound beam determined?

Crystals

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10

Axial Plane

  1. Along direction of sound travel

  2. Parallel

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11

Lateral Plane

Perpendicular to direction of sound travel

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12

Elevational Plane

Thickness of sound beam

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13

What produces the width of a sound beam? How is the width determined?

  1. Transducer

  2. The distance from the transducers face

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14

Is intensity uniform throughout a beam? Why?

  1. No

  2. Area varies (intensity = power/area)

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15

How are beam diameter and resolution related?

  1. Inversely

    1. Small beam = good resolution

    2. Large beam = bad resolution

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16

Near Zone

  1. AKA Fresnel zone, near field

  2. Region extending from transducer to minimum beam width

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Focal Point

  1. Smallest beam

  2. Maximum intensity

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18

When does a beam have the best resolution?

At the focal point

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19

Focal Zone

  1. Where beam is focused on each side of focal point

  2. Maximum

    1. Sensitivity

    2. Intensity

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20

When does a beam have the best lateral resolution?

At the focal zone

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21

How are diameter and intensity related in the focal zone?

  1. Inversely

    1. Diameter decreases = intensity increases

    2. Diameter increases = intensity decreases

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22

Near Zone Length (NZL)

  1. Distance from transducer face to where the beam has the smallest diameter

  2. Additional focusing can be added

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23

How are diameter and NZL related?

  1. Directly

    1. Increase diameter = increase NZL

    2. Decrease diameter = decrease NZL

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24

How are frequency and NZL related?

  1. Directly

    1. Increase diameter = increase NZL

    2. Decrease diameter = decrease NZL

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25

Far Field Divergence (FFD)

When the beam diameter increases after natural focus

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26

How are diameter and far field divergence related?

  1. Indirectly

    1. Increased diameter = Low divergence

    2. Decreased diameter = High divergence

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27

How are frequency and far field divergence related?

  1. Indirectly

    1. Increased frequency = Low divergence

    2. Decreased frequency = High divergence

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28

At a distance of one near zone length the diameter of the beam is…?

½ the crystal diameter

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29

At a distance of 2 near zone lengths the diameter of the beam is…?

The crystal diameter

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30

What two things does focusing contribute to?

  1. Better resolution (narrow beam)

  2. Stronger beam (decreased area)

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31

A-mode (Amplitude Mode)

  1. Displayed on graph

    1. X-axis = depth

    2. Y-axis = strength

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B-mode (Brightness Mode)

  1. 2D images, B-scans, displayed on a matrix

  2. Displayed dots with brightness

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33

What does brightness on B-mode show?

  1. Strength

  2. Location

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34

M-mode (Motion Mode)

  1. Displayed on a graph

    1. X-axis = time

    2. Y-axis = depth

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35

What imaging mode is used most used today?

B-mode

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36

What imaging mode is used for cardiac and fetal cardiac?

M-mode

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37

Transducer (Probe)

Device that converts one form of energy to another

<p><span style="font-family: sans-serif">Device that converts one form of energy to another</span></p>
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38

Bandwidth (BW)

Range of frequencies produced by the transducer

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39

How are pulse length and bandwidth diameter related?

  1. Inversely

    1. Short pulses = broad bandwidth

    2. Long pulses = narrow bandwidth

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40

Damping (Backing) Material

Epoxy resin attached to back of element

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41

What does damping material do?

  1. Absorbs vibrations

  2. Reduces #cycles/pulse

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42

How are pulse duration (PD) and spatial pulse length (SPL) related to resolution?

  1. Low PD and SPL = Improved resolution

  2. High PD and SPL = Reduced resolution

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43

How is bandwidth with damping related to quality factor, efficiency, and sensitivity?

  1. Inversely

    1. Increased bandwidth and damping = Decreased QF, efficiency and sensitivity

    2. Decreased bandwidth and damping = Increased QF, efficiency and sensitivity

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44

How are diagnostic imaging transducers damped? How many cycles per pulse does this produce?

  1. Highly damped

  2. 2-3 cycles per pulse

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45

How are pulsed-wave Doppler transducers damped? How many cycles per pulse does this produce?

  1. Less damped

  2. 5-30 cycles per pulse

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46

How are continuous wave Doppler transducers damped? Why?

  1. Not damped

  2. Reflects all energy into patient

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47

What does quality factor determine?

Sensitivity

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48

What does quality factor detect?

Weak echoes

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49

Quality Factor (QF) Formula

fo / BW

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50

Matching Layer

  1. Located on the transducer face

  2. Has impedance value between crystal and tissue

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51

What does the matching layer do?

Reduces reflection

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52

How are frequency and penetration related?

  1. Low frequency = Improved penetration

  2. High frequency = Reduced penetration

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53

How are penetration and resolution related?

  1. Improved penetration = Reduced resolution

  2. Reduced penetration = Improved resolution

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54

What is a complete scan of the ultrasound beam called?

Frame

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55

What is required for real-time scanning?

Transducer arrays

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56

What means are used for sweeping, steering, and focusing the beam? What is this accomplished by?

  1. Electronic means involving constructive interference

  2. Accomplished by

    1. Sequencing

    2. Phasing

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57

What is the time delay between pulses determined by?

Depth (time it takes for all echoes to return)

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58

Beam Steering

  1. Sweeping the beam

  2. Accomplished with phasing

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59

What does beam steering produce?

Automatic scanning

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60

How are time and beam steering related?

  1. Directly

    1. Increased delay = Increased steering

    2. Decreased delay = Decreased steering

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61

How do you know what direction a beam is going during beam steering?

  1. Beam goes toward side activated last

  2. Right to left = steered left

  3. Left to right = steered right

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62

How are time and focus related during electronic (transmit) focusing?

  1. Inversely

    1. Increased delay of curvature = Closer focus

    2. Decreased delay of curvature = Deeper focus

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63

Linear Array

  1. Straight line of elements

  2. Rectangular image

  3. Vertical, parallel scan lines

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What can be done during linear array to produce a parallelogram?

Can be steered to right or left (in Doppler)

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Curved (Convex) Array

  1. Curved line of elements

  2. Produces sector image

  3. Pulses travel in different directions from different origins

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66

Phased (Sector) Array

  1. Compact line of elements

  2. Produced pie shaped image

  3. Pulses travel in different directions from same origin

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67

What occurs during phased array?

Voltage pulses applied to entire group of elements with varying time delays = sweeping of beam

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68

Vector Array

Parallelogram-shaped display

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69

What is a 2D array? What can they do?

  1. Matrix of elements

  2. Ability to steer and focus in two dimensions

  3. Allows for focusing in elevational plane by phasing

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70

Name the three spatial categories of resolution

  1. Axial

  2. Lateral

  3. Elevational

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71

What does spatial resolution give us the ability to see?

Detail on an image

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72

What is spatial resolution related to?

  1. Directly related to # of scan lines

  2. Related to # of pixels in a monitor

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73

What size resolution is always better?

  1. Smaller

  2. Less distance between reflectors to be displayed as separate objects

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74

What is axial resolution?

The minimum reflector separation necessary to resolve reflectors parallel to sound beam

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75

What is axial resolution determined by?

SPL

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76

What does LARD stand for? (Has to do with AR)

Longitudinal, Axial, Range, Depth

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77

To improve AR, SPL must be _____

Reduced

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78

As SPL decreases, AR ____

Decreases

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79

As frequency increases, AR _____

Decreases

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80

Does axial resolution change with depth? Why?

  1. No

  2. AR is constant along beam path

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81

What is lateral resolution?

Minimum reflector separation necessary to resolve reflectors perpendicular to beam

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82

What is lateral resolution determined by?

Beam width

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83

Does lateral resolution vary with depth? Why?

  1. Yes

  2. Because of sound beam shape

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84

What does LATA stand for? (Has to do with LR)

Lateral, Angular, Transverse, Azimuthal

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85

Elevation resolution varies with ____ because of the shape of the sound beam

Depth

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86

What is contrast resolution?

The ability of gray-scale display to distinguish subtle differences in echogenicity, or brightness, of adjacent tissues

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87

What is contrast resolution determined by?

  1. Number of pixels in an image

  2. Number of shades of gray displayed in each pixel

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88

What is contrast resolution controlled by?

  1. System’s memory

  2. Dynamic range settings

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89

What is temporal resolution?

Ability to follow moving structures in temporal detail

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90

What is frame rate?

Number of images displayed per second

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91

Faster FR = _____ temporal resolution

Improved

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92

Frame Rate is dependent on… (5 things)

  1. Line density

  2. Lines per frame

  3. Depth & PRF

  4. Sector Width

  5. Number of foci

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93

What is line density?

  1. # of scan lines per degree of sector

  2. # of scan lines per centimeter

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94

What is lines per frame?

# of lines in each frame

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95

More lines = ____ spatial resolution

Improved

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96

How are line density and lines per frame related to FR?

Inversely

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97

____ sector width improves image quaility

Low

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98

Why does a low sector width improve image quaility?

  1. Less tissue interrogated

  2. Less artifacts

  3. Improved signal to noise ratio

  4. Improves contrast resolution

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99

Depth and PRF are ____ related

Inversely

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100

Depth is ____ related to FR

Inversely

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