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Inc > ASN Ultrasound Course > Flashcards

ASN Ultrasound Course Flashcards

1
Q

What determines lateral resolution

A

diameter of beams, narrower better lateral resolution

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2
Q

Why is high frequency better in terms of resolution?

A

Axial resolution improved because shorter pulses associated w/ high freq sound. Lat res improved b because high freq pulses diverge less from field.

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3
Q

How does axial resolution vary w/ depth

A

It doesn’t its same at all depth

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4
Q

How does lateral resolution vary w/ depth

A

Best resolution in the focus

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5
Q

What are 3 ways to focus ultrasound beam?

A

external focusing (with lens), internal focusing (with curved active element), phased array focusing (with electronics in ultrasound system).

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6
Q

What are effects associated with focusing

A

decreased size of focal zone, beam beyond focal zone widening.

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7
Q

What are two determinants of divergence?

A

High frequency and wider probe decrease divergence

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8
Q

What does A mode stand for?

A

amplitude mode

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9
Q

What creates large vs smaller spike on A mode

A

strong reflection creates tall spikes

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10
Q

Who uses A mode?

A

ophthalmology - where depth or structure thickness important

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11
Q

What are displayed on axis of B m mode?

A

Z amplitude, X depth, Y none

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12
Q

What are display mode axes with M-mode

A

x time, y depth, z none.

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13
Q

Describe mechanical transducor

A

single circular disc-shaped active element that is physically moved creating s can plane. Fixed focus adjustable only w/ internal or external focusing.

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14
Q

Describe transducor arrays

A

Single slab of PZT cut into collection of separate pieces called elements.

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15
Q

Describe linear phased arrays

A

Rectangular elements side by side width 1/4-1/2 wavelength. Beam steering occurs via electronic process called phasing.

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16
Q

How do you get a focused beam with a linear phased array?

A

With dome shaped arrival of electrical signal at transducer.

17
Q

Where is focus of smaller diameter PZT crystal vs bigger deeper or more shallow?

A

Smaller diameter = shallower

18
Q

What can annular phased array do?

A

It can focus at multiple depths simulataneously - inner core focuses more shallow and outer deeper.

19
Q

Describe linear sequential arrays?

A

Box with a bunch of rectangular arrays 120-250. Small group fired simulataneously

20
Q

How does beam focusing occure w/ linear sequential?

A

electronic focusing

21
Q

Image shape and size w/ linear sequential arrays?

A

rectangular. Never wider than the transducer.

22
Q

Why are multipole transducers fired at once?

A

To cancel out huygens wavelet theory (spherical shape) -take advantage of interference

23
Q

Can linear phased arrays be steered electronically?

A

Yes leading to parallelogram shaped images

24
Q

Can a curved version of linear array probes be made?

A

Oh yeah!

25
Q

Can linear and curvilinear array probes use dynamic receive focusing?

A

Yes

26
Q

What is elevational resolution?

A

Slice thickness

27
Q

What type of transducer has the best elevational resolution? And what is the elevation

A

disc shaped crystals such as those found in mechanical or annular phased array tranducers

28
Q

What are side lobes in ultrasound? What thype of transducer creates them?

A

Off axis sound beams. Can degrade lateral resolution. Single element transducer.

29
Q

What are grating lobes?

A

Similar to side lobes but create dby array tranducers. AAgain degrade lateral res and reduce image quality.

30
Q

How does apodization eliminate grating lobes?

A

By using lower voltage at edges of probe.

31
Q

How does subdicing reduce grating lobes?

A

By splitting up an element of linear array transducer into multiple sub elements acting together

32
Q

What technique is used to keep US beam narrow of substantial depth range? How does it work?

A

Dynamic aperature. Optimizes lateral resolution. Varies the number of crystals producing sound and narrowing element changing focus.

33
Q

What is name of firing pattern that steers and what is name of firing pattern that focuses linear phased array

A

electronic slope, electronic curvature

34
Q

What improves elevational resolution of linear array

A

one and a half dimensiional array

35
Q

What are two factors that determine temporal resolutio or frame rate n

A

sounds speed in medium and depth of imaging

36
Q

How does number of pulses affect temporal resolution

A

Pulses per frame and frame rate are inversely related. Lower number of pulses per image greater frame rate

37
Q

How do multiple foci affect the temporal resolution?

A

They improve lateral resolution, but worsen frame rate and worsen temporal resolution.

38
Q

What four parameters lead to higher frame rate (depth, focus, sector width, line density)

A

shallower, single focus, narrow sector, low line density

Inc (10 decks)

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