C4: Resolution Flashcards by M B

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

detail/spatial
contrast
temporal

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

axial
lateral
elevational/z-axis

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

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formula for axial resolution

AR=1/2(SPL)

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does axial resolution get better with increased frequency?

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

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list the 5 items that improve axial resolution

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

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what is LARD for axial resolution?

Longitudinal
Axial
Range
Depth

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is lateral resolution constant with depth?

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which type of resolution is typically the best?

axial

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list the 5 items that improve lateral resolution

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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what is LATA for lateral resolution?

Lateral
Angular
Transverse
Azimuthal

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what is slice thickness

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

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how do we focus in the z axis

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

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

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

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list the 4 items that improve elevational resolution

distance from the probe
higher frequency
NZL
amount of focusing in Z axis

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another term for the elevation plane

slick thickness

define contrast resolution

what does it depend on?

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

what happens when you have too little contrast?

too much?

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

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

yes

bistable

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

higher the bit depth the greater the shades of grey

whats another term for dynamic range?

compression

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

increase or decrease the dynamic range

what happens when we decrease the dynamic range?

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

whats temporal resolution (TR)

ability to see moving structures in real time

another word for TR

frame rate (FR)

what must the FR be > or = to?

20 fps

whats the relationship between PRF and temporal resolution?

increase in PRF will improve TR directly related

whats the formula for TR?

PRF (in Hz) = n x LPF x FR ``` n= # of foci LPF= lines per frame FR= frame rate (in Hz) ```

whats the range ambiguity formula? | what should this value be and why is this number used?

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

what limits the PRF?

depth or penetration of sound

list the 5 items that improve temporal resolution

- 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

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

yes

where r echo delays located?

beam former

which type of focusing provides uniformity through out the image?

receive focus

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

Damping

Is the axial resolution equal throughout the beam?

Yes

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

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

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

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