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Physics 2 > Chapter 12 > Flashcards

Chapter 12 Flashcards

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1
Q

what 2 characteristics of sound make it challenging to make two-dimentional images?

A

sound travels in a straight line and sound beams must be narrow to optimize lateral resolution

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2
Q

a modern ultrasound system sends a ______ sound pulse into the body, receives reflections, processes, and stores the data

A

narrow- sound beams are redirected into the body at different angles

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3
Q

to create a 10 centimeter deep image with 90 individual ultrasound pulses takes more than ______ of a second

A

1/100th

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4
Q

the mechanical transducer contains a _____,_____,_____ active element that is physically moved, this movement creates a scan plane

A

single, circular, disc-shaped

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5
Q

how many active elements does the mechanical transducer contain?

A

one- resembles a coin

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6
Q

the image created by a mechanical transducer is ______, similar to the sweeping of a wiper blade across a cars window. What does the pulse created look like?

A

fan or sector-shape

spokes of a bicycle wheel as it rotates around a single point

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7
Q

In mechanical with ______ depths, gaps of ever increasing size exist between the scan lines in mechanical transducers

A

greater

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8
Q

In mechanical transducer the two-dimentional image is built up by rotating the crystal with a motor, sound beams are emitted as the crystal moves, the scan plane is created through ______

A

mechanical steering

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9
Q

Mechanical transducers have a fixed depth called______

A

conventional, mechanical, or fixed focusing

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10
Q

What happens when a mechanical transducer’s PZT gets damaged?

A

They only have one so the entire image is lost

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11
Q

An array comprises a single slab of PZT cut into a collection of separate pieces called ______

A

Elements-each one is acoustically isolated from its neighboring crystals

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12
Q

A ______ is the combination of the active element, wire, and system electronics

A

Channel

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13
Q

What is the size of the footprint on a linear phased array?

A

1 centimeter on each side

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14
Q

In linear phased array the beam is steered and focused using an electrical technique called _____, it also builds up the 2 dimensional images

A

Phasing

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15
Q

How many elements does a linear phased array have?

A

Between 100 to 300- they are rectangular and narrow, a width of 1/4 to 1/2 of the sounds wavelength

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16
Q

What shape does a phased array make?

A

Fan or sector-shaped

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17
Q

In linear phased array, the pulses re directed in a pattern similar to that of the sweeping of a ______

A

Windshield wiper

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18
Q

With phased array systems what can the sonographer modify?

A

The depth and amount of focusing of the sound beam

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19
Q

The phased array can transmit multiple beams down the same scan line, each with a different focal depth, thus providing ______ capability

A

Multi-focusing

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20
Q

What happens to a linear phased array if a Crystal gets damaged?

A

Inconsistent or erratic beam steering and focusing

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21
Q

how many active elements in a phases array probe are used to create a single sound?

A

all the active elements are fired, they all create small sound wavelets. they interfere constructively and destructively creating a single sound pulse with perpendicular characteristics, the patten determines the beams direction and focus

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22
Q

in phased array, how does the pattern of electrical spikes from the US system steer the sound beam in different directions?

A

the spikes travel down the wire and excite the active elements at the end of the wires, the electrical signals are lined up and will arrive at each of their respective PZTs at exactly the same time. their wavelets interfere forming a single sound beam

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23
Q

what are the 2 steps to determine the direction that the sound beam will transmit?

A
  1. draw a line that connects the electrical spikes

2. draw another line extending out of the transducer that is perpendicular to the solid line

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24
Q

the electrical signals are separated by ______ of a second

A

one billionths (10 nanoseconds)

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25
Q

the infinitesimal time differences between many wavelets create a single unified sound beam that is directed, these time differences are called______

A

phased delay

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26
Q

beam steering is achieved ______ without any moving parts in the transducer

A

electronically

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27
Q

the electronics within the ultrasound system that create the beam steering patterns is called the ______

A

beam former

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28
Q

what will happen if the spike pattern is a straight line?

A

on unfocused sound beam is created

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29
Q

how does the pattern of electrical spikes from the beam former focus the sound beam during transmission?

A

the outer crystals are excited earlier than the inner crystals, the curved pattern creates a focused sound beam during transmission

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30
Q

what happens when the electrical spikes pattern is convex with an outward or D-shape?

A

it creates a defocused beam, has no use

31
Q

how does a phased array system create images with multiple transmit foci?

A

the US system sends multiple sound beams down each scan line, each electrical spike pattern has a different degree of curvature

32
Q

with multi focus the pattern with the greatest curvature creates the beam with the ______ focus, the pattern with the least curved produces the beam with the ______ focus

A

shallowest, deepest

33
Q

During receptions, when reflected sound arrives at the transducer, multiple neighboring elements in the probe are excited; these elements create electrical signals that return to the systems receiver via ______.

A

multiple channels

34
Q

a more accurate images can be created when the US receiver introduces ______ to some of these electrical signals during reception

A

variable time delays; the delay patterns during receive-focusing changes continuously as the transducer listens for reflections

35
Q

with ______ focusing, the reflected sound is focused at many depths

A

dynamic receives (preformed automatically by system)

36
Q

the active elements of annular array transducers appear ______.

A

disc-like; comprises multiple ring-shaped elements with a common center

37
Q

with annular transducers, ______ creates the two-dimenstional image

A

mechanical steering- a motor physically moves the ringed element array so that the sound beams are transmitted in different directions

38
Q

what is the primary advantage of annular phased arrays?

A

multiple transmit focal zones create each scan line of the image

39
Q

the inner crystal of an annular phased array transducer creates a ______ focus beam and information only from the shallowest depths is collected

A

shallow-imformation is stored only from the respective focal zone, which gets progressively deeper with every ring

40
Q

what is the image shape of a annular phased array transducer?

A

fan or sector shaped

41
Q

what happens if an annular phased array transducer PZT gets damaged?

A

a horizontal line or side-to-side band of dropout at a particular depth is seen

42
Q

what does the linear sequential arrays transducer look like?

A

it has a large acoustic footprint and creates rectangular images

43
Q

a linear sequential array has ______ rectangular-shaped strips of piezoelectric material arranged side by side in a line

A

120 to 250; each crystal is about 1 wavelength in width and up to 10 cm long

44
Q

how does the beam steer in the linear sequential arrays?

A

a small group of the crystals are fired simultaneously to create each sound beam, the sound beams are parallel to each other and are typically directed straight ahead

45
Q

How does the linear sequential arrays focus?

A

they preform both transmit and receive focusing using electronic phase delays
transmit focusing-curved excitation pattern of the active element (outer PZT are fired earlier than inner)
receive focusing- electrical delays in the signals returning from the transducer

46
Q

what is the shape of the linear sequential arrays?

A

rectangular shaped, the image is never wider than the transducer

47
Q

what happens when a linear sequential PZT is damaged?

A

only a portion of the image is non visible (from top to bottom)

48
Q

what would happen if only a single crystal was fired instead of groups?

A

the beam would quickly diverge and result in poor lateral resolution

49
Q

what happens to a linear sequential array if you use beam steering?

A

creates a parallelogram-shaped image

50
Q

what is the number and shape of the crystals in a curved array transducer?

A

120 to 250 rectangular shaped strips of PZT material arranged side by side in a bowed line, the array is large, the foot print can be as long as 10 cm and 1 wavelength wide

51
Q

in curved array the beam is directed straight out of the crystals, but since the crystals are arranged in an arc, the pulses travel in ______ as they radiate out from the transducer

A

different directions (not parallel)

52
Q

what is the image shape of the curved array?

A

blunted sector-shaped

53
Q

what happens if a PZT is damaged in a curved array?

A

a section from top to bottom is non visible

54
Q

what is a vector array a combination of?

A

linear sequential and linear phased array; sloped phased delay patterns can electronically steer the sound beam in different directions

55
Q

what is the number and shape of the crystals in vector arrays?

A

there are 120-250 rectangular shaped strips of PZT, the footprint is small

56
Q

the electrical signals from the beam former are delayed in a ______ pattern as they excite a group of elements in a vector array, as a result the beam radiates out in different directions from the face of the transducer

A

sloped spike-line

57
Q

______ is used in vector arrays, both transmit focusing and dynamic receive focusing improve lateral resolution over a great range of depths

A

electronic focusing

58
Q

what image shape does the vector array make?

A

a trapezoidal image

59
Q

what are the 3 dimensional space that resolution deals with?

A

shallow-to-deep, side-to-side, and above-to-below

60
Q

______ is measured in a direction perpendicular to the imaging plane or above-to-below the imaging plane

A

slice thickness- the the slice is thick, structures above and below the plane create reflections that appear in the image

61
Q

what shape of active element creates the best elevational resolution?

A

disc shaped PZT provide the thinnest US slices and best elevational resolution within the focal zone (found in mechanical and annular phased array)

62
Q

the elevational resolution is identical to the ______ resolution with disc-shaped active elements

A

lateral

63
Q

what determines elevational resolution in phased array, linear, and curved array transducers?

A

on acoustic lens is used to create a thinner slice, with these axial resolution is best then lateral then elevational

64
Q

a 2-D array with thousands of elements arranged in a checkerboard pattern, creates ______ images

A

3-D

65
Q

with 2-D array transducers, the sound beams are electronically focused in both the ______ and ______ planes

A

lateral and thickness

66
Q

______ is simply a trendy way of describing real-time 3-D imaging

A

4-D (also uses 2-D array probes)

67
Q

______ creates an image from three-dimensional data acquired during the ultrasound exam, uses color shadows, texture, and optical effects

A

rendering- provides an element of realism to the image, usually on an off line stand alone computer system

68
Q

______ is on off axis sound beam, outside of the main beam in the far zone

A

side lobe- reflections arising within the side lobe degrade lateral resolution

69
Q

______ is the same as side lobe, but they are created by array transducers

A

grating lobe

70
Q

reducing the strength of a side lobe or grating lobe can be done through a process called ______

A

apodization- stronger signals are used to excite the inner crystals, and progressively weaker electrical spikes excite the out crystals

71
Q

______ of each element in a linear array transducer also reduces grating lobes

A

subdicing- a crystal is divided into a group of smaller crystals called sub-elements (join to act as a single crystal)

72
Q

a technique called ______ can be used to make a sound beam narrow over a greater range of depths and thus optimize lateral resolution

A

dynamic aperture (also known as changing aperture or variable aperture)- when a array transducer is used, the US system may change the number of crystals along the face used to transmit and receive reflections

73
Q

the aperture may be thought of as the ______ or the ______ that is, the number of elements used to create sound beams or to receive reflected echoes

A

“transmit hole”, “listening hole”

Physics 2 (11 decks)

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