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Ultrasound Physics > 10 2-D Imaging > Flashcards

10 2-D Imaging Flashcards

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1
Q

What are B-scans or B-modes?

A

2-D images

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2
Q

What does a scanhead contain?

A

1 disc-shaped, element (like a coin)

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3
Q

What is steering in mechanical scanning?

A

The active element is moved by a motor, oscillating crystal or mirror through a pathway

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4
Q

What is focusing in mechanical scanning?

A

Conventional or Fixed - curvature (internal) of the PZT or an acoustic lens (external) focuses the beam at a specific depth

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5
Q

What is the image shape of a mechanical transducer?

A

Fan or sector-shaped

Scan lines spread apart creating gaps at greater depths

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6
Q

What does a defective crystal cause in a mechanical transducer?

A

Destroys entire image

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7
Q

What is a transducer array?

A

A collection of active elements in a single transducer

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8
Q

What is an element of a transducer array?

A

The separate pieces of a single slab of a PZT

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9
Q

What is the channel of transducer array?

A

Combination of electronic circuitry, the wire and the element

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10
Q

What is a linear array of a transducer?

A

A collection of elements in a line

  1. Linear switched array
  2. Linear phased array
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11
Q

What is an annular array of a transducer?

A

A group of ringed elements with a common center

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12
Q

What is a convex, curved, or curvilinear array?

A

Elements arranged in an arc

  1. Convex switched (or sequential) array
  2. Convex phased array
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13
Q

What are the # and shape of the crystals in a linear switched array?

A

Large transducers with approx 200 rectangular-shaped elements

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14
Q

What creates a narrow directional beam?

A 
Few elements (3-10), but not all, are fired at exactly the same time 
This improves lateral resolution
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15
Q

What type of steering occurs in linear switched arrays?

A

Steering = Pulses sent down parallel lines
The scan lines are parallel and remain equally spaced at all depths
None in linear switched arrays

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16
Q

What type of focusing occurs in linear switched arrays?

A

Focusing = Lens (external) or curved crystal (internal)

Fixed

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17
Q

What is the image shape of linear switched arrays?

A

Rectangular image shape, no wider than the transducer

18
Q

What are linear phased arrays?

A

Adjustable focus or multi-focus

19
Q

What are the # and shape of crystals in a linear phased array?

A

Approx 200 rectangular-shaped elements arranged in a line

20
Q

What is the focusing and steering in a linear phased array?

A

Electronic

A collection of electric pulses delivered to all of the transducer’s elements in various patterns for each sound pulse

21
Q

What is the image shape of a linear phased array?

A

Fan or sector-shaped

22
Q

What is phasing?

A

Minuscule time delays (10 ns) between electronic pulses delivered to the individual array elements

23
Q

What does a defective crystal cause in a linear phased array?

A

If one element malfunctions, the steering and focusing become erratic

24
Q

What is the electronic slope?

A

Creates beam steering

25
Q

What is the electronic curvature?

A

Creates beam transmit focusing

26
Q

What is a beam former?

A

Creates the electronic patterns

Delays are approx 10 ns

27
Q

What is dynamic receive focusing?

A

Phase delays during reception can be applied to the electrical signals from the transducer to the US system which provides focusing at many depths during reception

28
Q

How are the crystals arranged in an annular phased array?

A

Concentric rings cut from the same circular slab of PZT - looks like a bull’s eye target

29
Q

What is the shape of the crystals in an annular phased array?

A

Small # of ring-shaped elements

30
Q

How are the crystals arranged in an annular phased array?

A

Selected focal zones, use inner crystals for shallow regions and outer crystals for deep regions

31
Q

What is the image shape of an annular phased array?

A

Fan or sector-shaped

32
Q

How is the focusing in an annular phased array?

A

Multi-focusing, provides electronic focusing in all planes at all depths
Provides optimal lateral resolution at all depths throughout the image

33
Q

What is the steering in an annular phased array?

A

Mechanically

34
Q

What occurs with a defective crystal of an annular phased array?

A

Horizontal (side-to-side) band of dropout

35
Q

What does a convex or curved array do?

A

Piezoelectric crystals arranged in a curve to provide a natural sector image

36
Q

What is the image shape of a convex array?

A

Blunted-sector, fan shaped image

37
Q

What does a large convex or curved array large transducer provide?

A

Convex sequential arrays place a large acoustic footprint on the patient

38
Q

What creates 3-D or 4-D images?

A

2-D arrays

39
Q

What do 1 1/2-dimensional arrays allow?

A

Focusing in the plane of the image making a thinner slice which improves the elevational resolution

40
Q

What are vector arrays?

A

Combination of linear sequential and linear phased array

41
Q

What is the image shape of a vector array?

A

Trapezoidal - a sector with a flat top that does not come to a point

Ultrasound Physics (20 decks)

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