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Physics 3 > Chapter 21 Part 2 > Flashcards

Chapter 21 Part 2 Flashcards

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0
Q

T or F

Lobe artifact degrades lateral resolution

A

True

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1
Q

________ artifact appears when sound energy is transmitted in a direction other than along the beams main axis.

A

Lobe

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2
Q

T or F

Lobes are weaker than the primary beam and do not typically create reflections that appear on an image.

A

True

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3
Q

What are the 2 characteristics of lobe artifact?

A
  • a second copy of the true reflector

- the artifact and the true reflector are located side by side at the same depth

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4
Q

What are lobes called when created by a single crystal transducer, such as a mechanical probe?

A

Side lobes

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5
Q

What are lobes called when created by array transducers?

A

Grating lobes

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6
Q

A process of dividing each PZT element into small pieces is called?

A

Subdicing

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7
Q

_________ lobe artifact can be reduced by subdicing

A

Grating

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8
Q

T or F

Grating lobes can be further reduced by exciting the subdiced elements with different voltage

A

True

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9
Q

Elements closer to the center of the sound beam are excited with higher voltages, while the outermost elements are excited with lower voltages. This process is called?

A

Apodization

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10
Q

2 methods to eliminate lobes

A
  • Subdicing

- Apodization

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11
Q

What artifact is created when a sound pulse changes direction during transmission?

A

Refraction

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12
Q

Refraction is transmission with a _________.

A

Bend

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13
Q

T or F

Refraction artifact degrades lateral resolution

A

True

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14
Q

What are the 2 characteristics of refraction?

A
  • a second copy of the reflector

- the copy is side by side, or at the same depth as the true reflector

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15
Q

What are two other names for slice thickness?

A
  • section thickness artifact

- partial volume artifact

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16
Q

Slice thickness artifact is related to the dimension of the _________ that is perpendicular to the imaging plane.

A

Beam

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17
Q

_________ is determined by the thickness of the imaging plane.

A

Elevational resolution

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18
Q

The _______ reflector lies either above or below the assumed imaging plane, but is displayed within the image.

A

True

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19
Q

T or F

Slice thickness artifact fills in hollow structures such as cysts.

A

True

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21
Q

Slice thickness artifact is _______ (increased or reduced) with thinner imaging planes, such as those created by one half dimensional array transducers.

A

Reduced

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22
Q

________ resolution artifact occurs when a pair of side-by-side reflectors are closer than the width of the sound beam.

A

Lateral

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23
Q

T or F

In regards to lateral resolution, the reflectors are positioned perpendicular to the beam.

A

true

24
Q

With lateral resolution, two objects appear as ______ reflection on the image.

A

one

25
Q

Lateral resolution artifact may display a small reflector as a __________ rather than a narrow dot.

A

wide line

26
Q

What is another name for lateral resolution artifact?

A

point spread artifact

27
Q

T or F

Lateral resolution artifact is most likely to occur where the beam is smallest.

A

false

28
Q

T or F

lateral resolution is least likely to occur at focus where beam diameter is smallest.

A

true

29
Q

_________ resolution artifact is created when a long pulse strikes two closely spaced structures, where one is in front of the other.

A

Axial

30
Q

With axial resolution artifact, the structures are __________ to the beam’s main axis.

A

parallel

31
Q

T or F

Axial resolution artifact creates one reflection on the image from two closely spaced reflectors.

A

true

32
Q

T or F

Transducers that create long pulses minimize axial resolution.

A

false

33
Q

What artifact is created when sound pulses glance off a second structure on the way to or from the primary reflector?

A

Multipath artifact

34
Q

What type of reflectors redirect sound waves in directions other than back toward the transducer?

A

Curved or oblique

35
Q

The ability to precisely locate a moving structure at all times is called?

A

Temporal resolution

36
Q

Temporal resolution is best with high or low frame rates?

A

high frame rates

37
Q

Spatial resolution is related to the ___________ in an image.

A

overall detail

38
Q

What are the factors that spatial resolution is determined?

A
  • line density
  • axial resolution
  • lateral resolution
39
Q

When is spatial resolution exceptional?

A

with high line density (closely packed sound pulses)

40
Q

When is spatial resolution poor?

A

with low line density (wider gaps between the sound pulses)

41
Q

When image information is displayed on a monitor, spatial resolution is affected by the number of ____________ scan lines per frame.

A

horizontal

42
Q

T or F

More lines on a monitor provide better spatial resolution.

A

True

43
Q

When the image information is in digital form, spatial resolution is related to __________.

A

pixel density

44
Q

T or F

Higher pixel density results in better spatial resolution.

A

true

45
Q

What artifact occurs when the pixel size is greater than the size of the reflector?

A

Spatial resolution artifact

46
Q

What artifact occurs when a reflecting structure is located deeper than the imaging depth of the image?

A

Range ambiguity artifact

47
Q

Range ambiguity artifact is eliminated by ________ (increasing or decreasing) the pulse repetition period.

A

increasing

48
Q

What appears as small amplitude echoes and results from many sources, including electrical interference, signal processing, and spurious reflections?

A

Noise

49
Q

T or F

Noise is more likely to affect low-level hypoechoic regions rather than bright echogenic areas.

A

true

50
Q

Noise resulting from the constructive and destructive interference of small sound wavelets is known as?

A

acoustic speckle

51
Q

____________ interference occurs when wavelets are in-phase.

A

Constructive

52
Q

____________ interference occurs with out of phase wavelets.

A

Destructive

53
Q

______________ is an effective tool to reduce speckle.

A

Spatial compounding

54
Q

Another form of noise, with the presence of false echo signals arising from locations outside of the main sound beam is?

A

Clutter

55
Q

Side lobes, grating lobes, and section thickness artifact are sources of _________.

A

Clutter

56
Q

What reduces an image’s noise content?

A

Harmonic imaging

57
Q

What is the goal of harmonic imaging?

A

To selectively distinguish meaningful reflections from noise, increasing the signal to noise ratio

Physics 3 (7 decks)

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