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Physics > Lecture 17 > Flashcards

Lecture 17 Flashcards

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1
Q

Linear phased array is a ____ line of elements

A

Straight

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2
Q

In Linear phased array elements are fired with

A

A small time difference —> phasing

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3
Q

______us of time delay between each firing

A

<1us

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4
Q

Wave front created by the

A

Differing distances of the waves do to phasing

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5
Q

A wave always travels ______ to its wave front

A

Perpendicular

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6
Q

The new waveform created by secondary wavelets happens according to

A

Huygens principle

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7
Q

How do we stear a beam to the right

A

Phase the fire with the left side firing first

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8
Q

If all elerments are energized simultaneously then

A

There are no delays

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9
Q

The shorter the the delay between firing in elements than

A

The more horizontal the wavefront

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10
Q

How do we change the focus

A

Increase intensity —> improves intensity

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11
Q

Where is the beam width the smallest

A

At the focus

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12
Q

In electronic focusing the phased arry can also

A

Focus the beam

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13
Q

In electronic focusing greater durvature places the focus

A

Closer to the transducer

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14
Q

In electronic focusing less curvature moves focus

A

Deeper

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15
Q

In electronic focusing can move focus depth up or down based on the

A

Time delay

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16
Q

Greater time delay = _____ focus

A

Closer to the surface

17
Q

How do we achieve curvature

A

Fire outside crystals first and fire the middle ones the last

18
Q

an unfocused sound beam has

A

Natural focusing

19
Q

Focus sound beam has

A

Electronic focussing

20
Q

Multiple foci

A

They require multiple pulses, each focused at a different depth

Montage of overlaid images, better resolution at each depth

Decrease frame rate is lag

21
Q

What is a further application for phasing

A

Spatial compounding

22
Q

What is the purpose of spatial compounding

A

Hit the same object from different angles

23
Q

Spatial compounding has more

A

Pulses per image

Allows to sharpen boarders, smoother image, clears out cysts

24
Q

Phasing of a very small group of elements =

A

Sector image

25
Q

Phased array can be used to assess

A

Large ares through very small windows

26
Q

Phasing can be applied to each element group in a linear sequenced array to do the following :

A

Steer pulses in various directions

Initiate pulses at various starting points across the array

27
Q

Vector aray is _____+ _____

A

Linear array + phased array

28
Q

Vector array has a _____ top

A

Flat

29
Q

Widescreen =

A

Sector

30
Q

Vector array used to measure

A

Larger organs

31
Q

In vector arrays, phasing applie to linear sequence array….

A

Keep delays the same for each group

Beams sent out in an angled direction

Parallelogram shaped display

Used in doppler ultrasound

32
Q

Variable aperture

A

Not all elements of a phased array are used to generate all pulses

Smaller groups are used for short focal lengths

Larger groups for foci located at increasing depths

33
Q

Two types of grating lobes

A

Sides lobes

Grating lobes

34
Q

Side/grating lobes are ______ beams

A

Weaker

35
Q

Grating lobes are from _________ interactions

A

Interelement

36
Q

If side lobes/ grating lobes hit a strong reflector, they produce

A

Strong echoes

Examples of strong reflectors (diaphragm, gas, fetal bone)

37
Q

Side lobe and grating lobes show as ____ that look like ______

A

Artifacts

Amniotic bands

38
Q

How do we fix grating lobes? (3)

A

Apodization
Subdicing
THI

39
Q

Apodization

A

Grating lobes come from the edges of the elements

We can reduce the amplitude of the voltage to the outside elements

The weaker beam going out results in weaker echo, allowing for less artifacts to be created

Physics (32 decks)

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