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Physics 2 > C4: Resolution > Flashcards

C4: Resolution Flashcards

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1
Q

resolution can be broken down into what 3 main groups/aspects?

A

detail/spatial
contrast
temporal

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2
Q

what are the 3 main groups of detailed/spatial resolution?

A

axial
lateral
elevational/z-axis

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3
Q

if structures are closer to one another than 1/2(SPL) will they be resolved?

A

No

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4
Q

formula for axial resolution

A

AR=1/2(SPL)

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5
Q

does axial resolution get better with increased frequency?

A

yes…. because as F increases, lamda decreases which shortens the SPL

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6
Q

list the 5 items that improve axial resolution

A 
higher frequency
shorter wavelength
increased damping (because it reduces RD and SPL)
wider bandwidth
lower Q factor
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7
Q

what is LARD for axial resolution?

A

Longitudinal
Axial
Range
Depth

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8
Q

is lateral resolution constant with depth?

A

no

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9
Q

which type of resolution is typically the best?

A

axial

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10
Q

list the 5 items that improve lateral resolution

A
  • distance from the probe (reflector and focus)
  • amount of focusing (increased focusing gives us better lateral resolution
  • size of aperture
  • higher frequency
  • NZL
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11
Q

what is LATA for lateral resolution?

A

Lateral
Angular
Transverse
Azimuthal

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12
Q

what is slice thickness

A

that ability to separate reflects perpendicular to the image plane of the beam

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13
Q

how do we focus in the z axis

A

mechanically with a lens or acoustic mirror unless you have a 1.5D probe

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14
Q

if a structure is smaller than the beam thickness, will it be resolved well?

A

No. you will get a slice thickness artifact that will put fake echos into anechoic structures

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15
Q

list the 4 items that improve elevational resolution

A
  • distance from the probe
  • higher frequency
  • NZL
  • amount of focusing in Z axis
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16
Q

another term for the elevation plane

A

slick thickness

17
Q

define contrast resolution

what does it depend on?

A

the ability to distinguish between like shades of grey

it depends on the systems bit depth which determines the number of shades of grey you can produce

18
Q

what happens when you have too little contrast?

too much?

A

too little: the shades of grey are too similar to one another so you have no tissue differentiation

too much: similar shades of grey are grouped together and you can cant tell them apart

19
Q

can you have good contrast but poor contrast resolution? give and example

A

yes

bistable

20
Q

whats the relationship between bit depth and the number of shades of grey

A

higher the bit depth the greater the shades of grey

21
Q

whats another term for dynamic range?

A

compression

22
Q

how can you change the number of shades of grey shown on the monitor?

A

increase or decrease the dynamic range

23
Q

what happens when we decrease the dynamic range?

A

fewer shades of grey are displayed which can improve out ability to distinguish between them

24
Q

whats temporal resolution (TR)

A

ability to see moving structures in real time

25
Q

another word for TR

A

frame rate (FR)

26
Q

what must the FR be > or = to?

A

20 fps

27
Q

whats the relationship between PRF and temporal resolution?

A

increase in PRF will improve TR

directly related

28
Q

whats the formula for TR?

A

PRF (in Hz) = n x LPF x FR

n= # of foci
LPF= lines per frame
FR= frame rate (in Hz)
29
Q

whats the range ambiguity formula?

what should this value be and why is this number used?

A

penetration x n x LPF x FR

should be < or = 77,000 cm/s
-number is used because its half the avg. speed of sound in soft tissue

30
Q

what limits the PRF?

A

depth or penetration of sound

31
Q

list the 5 items that improve temporal resolution

A
  • depth of penetration (deeper = lower TR, b/c it takes longer for sound to return to the probe)
  • # of foci (more foci decreased FR because you must use more pulses per scan lines to create multiple areas of focus)
  • lines per frame (fewer lines = better TR)
  • sector width (lower sector means fewer scan lines for improves TR)
  • FR
32
Q

Does a fixed focus mean that you have a fixed NZL?

A

yes

33
Q

where r echo delays located?

A

beam former

34
Q

which type of focusing provides uniformity through out the image?

A

receive focus

35
Q

How do we reduce the number of cycles in the pulse?

A

Damping

36
Q

Is the axial resolution equal throughout the beam?

A

Yes

37
Q

What’s the minimum number of rows of crystals you need to focus in the elevational plane

A

3

The additional 2 rows on the edge should be half the length of the central row of crystals

38
Q

If you want to double your FR what can you change?

A 
1/2 the depth of interest
Or
1/2 the number of scanlines
Or
remove one foci

Physics 2 (7 decks)

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