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Ultrasound Physics > Ch 10: Axial & Lateral Resolution > Flashcards

Ch 10: Axial & Lateral Resolution Flashcards

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1
Q

Define ‘resolution’.

A

The ability to create accurate images

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2
Q

Define ‘axial resolution’.

A

The ability of a system to display two structures that are very close together when the structures are parallel to the sound beam’s main axis.

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3
Q

Axial resolution is measured in units of…

A

distance, mm.

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4
Q

Axial resolution is determined by…

A

both the sound source and the medium (like spatial pulse length).

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5
Q

T/F? Longer pulses improve axial resolution.

A

FALSE, *shorter

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6
Q

The synonyms of axial resolution are…

A

longitudinal, range, radial, or depth resolution.

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7
Q

Is axial resolution adjustable?

A

No

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8
Q

In clinical imaging, axial resolution ranges from…

A

0.1 to 1.0 mm.

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9
Q

___ numerical values indicate shorter ___ and improved image quality.

A

Lower, pulses

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10
Q

Spatial pulse length (mm) divided by 2 =

A

axial resolution (mm)

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11
Q

Wavelength (mm) times # cycles in pulse divided by 2 =

A

axial resolution (mm)

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12
Q

A short pulse is created in what two ways?

A
  1. less ringing

2. higher frequency

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13
Q

Better axial resolution is associated with ___ spatial pulse length, ___ pulse duration, and ___ frequencies.

A

shorter, shorter, higher

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14
Q

Better axial resolution is associated with ___ cycles per pulse and ___ numerical values.

A

fewer, lower

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15
Q

Define ‘lateral resolution’.

A

The ability to distinctly identify two structures that are very close together when they are side by side, or perpendicular, to the sound beam’s main axis.

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16
Q

Lateral resolution is measured in units of…

A

distance, mm.

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17
Q

Lateral resultion is determined by…

A

the width of the sound beam.

18
Q

Narrower beams have ___ resolution.

A

better

19
Q

Lateral resolution is also called…

A

angular, transverse, or azimuthal resolution.

20
Q

Lateral resolution is best at the focus where the beam is…

A

narrowest.

21
Q

lateral resolution (mm) =

A

beam diameter (mm)

22
Q

Which type of resolution is better in clinical imaging systems?

A

axial resoltution

23
Q

The numerical value for axial resolution is ___ the value for lateral resolution.

A

less than

24
Q

When using a high frequency transducer, axial resolution is improved in the ___ because ___ pulses are associated with higher frequency sound.

A

entire image, shorter

25
Q

When using a high frequency transducer, lateral resolution is improved in the ___ because high frequency beams are ___ lower frequency beams.

A

far field only, narrower than

26
Q

Name three methods of focusing.

A
  1. external
  2. interal
  3. phased array
27
Q

What type of focusing uses a lens?

A

external

28
Q

What type of focusing uses a curved active element?

A

internal

29
Q

What type of focusing uses the electronics of the u/s system?

A

phased array

30
Q

___ includes borth external and internal techniques.

A

Fixed focusing

31
Q

As the arc of the acoustic lens becomes more prominent, the degree of focusing ___ and the beam ___ in the focal zone.

A

increases, narrows

32
Q

As the curvature of the PZT becomes more pronounced, the degree of focusing ___.

A

increases

33
Q

There is no lens with ___ focusing.

A

internal

34
Q

Phased array focusing may only be used on ___ transducers, never on ___ transducers.

A

multi-element, single crystal

35
Q

When a sound beam focuses, the diameter in the near field and the focal zone…

A

narrows.

36
Q

When a sound beam focuses, the focus is moved ___ to the transducer.

A

closer

37
Q

When a sound beam focuses, the near zone length is…

A

reduced.

38
Q

When a sound beam focuses, the diameter beyond the focal zone…

A

widens.

39
Q

When a sound beam focuses, lateral resolution in the near and focal zones ___ and lateral resolution beyond the focal zone ___.

A

improves, degrades

40
Q

When a sound beam focuses, the size of the focal zone is…

A

reduced.

Ultrasound Physics (23 decks)

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