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CMI 350 > Ch. 10 Axial and Lateral Resolution > Flashcards

Ch. 10 Axial and Lateral Resolution Flashcards

1
Q

Resolution

A

is the ability to create accurate images.
(image accuracy is the essence of ultrasound)

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2
Q

Axial Resolution

A

describes one measure of the detail found in an image. It measures 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 units

A

measured in mm or any unit of distance

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4
Q

Axial Resolution determined by

A

both the sound source and medium

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5
Q

Axial Resolution is related to

A

Spatial Pulse Length
(both sound & medium)
Pulse Duration

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6
Q

Shorter Pulses improve

A

axial resolution

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7
Q

In a particular medium, short duration pulses also have a

A

a short length

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8
Q

Axial Resolution synonyms (4)

A

Longitudinal
Axial
Range
Radial
Depth resolution
(LARRD)

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9
Q

Axial Resolution adjustable

A

No, since the spatial pulse length for a transducer is fixed.

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10
Q

Axial Resolution typical values

A

ranges from 0.1 to 1.0 mm
(lower numerical values indicate shorter pulses and improved image accuracy)

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11
Q

What is the relationship btw the numerical value of the axial resolution and the image quality?

A

directly related
lower numerical values of axial resolution indicate a shorter pulse

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12
Q

Shorter pulses create

A

more accurate images

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13
Q

Axial Resolution formula

A

Axial (mm) = spatial pulse length (mm) / 2
or
Axial (mm) = wavelength (mm) x # cycles in pulse / frequency (MHz)

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14
Q

What allows some transducers to have better axial resolution than others?

A

determined by the pulse length, with shorter pulses yielding improved axial resolution

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15
Q

A short pulse is created in two ways:

A

1) less ringing
2) higher frequency

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16
Q

Less Ringing

A

A pulse is short if there are few cycles in the pulse

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17
Q

One way to reduce ringing is to

A

dampen the crystal after it has been excited by an electrical signal from the system.

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18
Q

Higher Frequencies

A

a pulse is short if each cycle in the pulse has a short wavelength

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19
Q

Shorter wavelengths are characteristics of

A

higher frequency sound

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20
Q

Pulses made of higher frequency cycles have

A

superior axial resolution

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21
Q

Better axial resolution is associated with (5)

A

1) Shorter spatial pulse length
2) Shorter pulse duration
3) Higher frequencies (shorter wavelength)
4) Fewer cycles per pulse (less ringing)
5) Lower numerical values

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22
Q

Lateral Resolution

A

is 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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23
Q

Lateral Resolution units

A

mm, cm, or any unit of distance
(Smaller # are preferable since they indicate more accurate images)

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24
Q

Lateral Resolution determined by

A

width of the sound beam; narrower beams have better resolution

25
Q

Lateral Resolution synonyms

A

Lateral
Angular
Transverse
Azimuthal
(LATA)

26
Q

Lateral Resolution is best at the

A

focus (at the end of the near zone) where the beam is narrowest. Lateral Resolution is good within the focal zone

27
Q

Lateral Resolution (mm) =

A

Beam diameter (mm)

28
Q

Which type of resolution is better in clinical imaging systems: lateral resolution or axial resolution ?

A

axial resolution is better bc pulses are shorter than they are wide. The numerical value is less too.

29
Q

What appears on an image when two reflectors positioned perpendicular to the sound beam are closer to each other than the beam width?

A

when two side by side reflectors are closer to each other than the width of the beam, only one reflection is observed on the image

30
Q

With regard to resolution, what are the advantages of using a high frequency transducer?

A

Higher frequencies improve both axial and lateral resolution

31
Q

Axial resolution is improved in the

A

entire image bc shorter pulses are associated with high frequency sound

32
Q

Lateral resolution is improved in the

A

far field only bc high frequency pulses diverge less in the far field than low frequency pulses. Higher frequency sound beams are narrower than lower frequency sound beams.

33
Q

Axial:
Orientation
Mnemonic
Determined by
Best with
Does it change?
In Near field, best with
In Far field, best with

A

1) front-back, parallel to beam
2) LARRD
3) Pulse length
4) Shortest pulse, highest frequency & fewest cycles
5) same at all depths, does not change
6) shortest pulse
7) shortest pulse

34
Q

Lateral:
Orientation
Mnemonic
Determined by
Best with
Does it change
In Near field, best with
In Far field, best with

A

1) side by side, perpendicular to beam
2) LATA
3) Beam width
4) Narrowest beam
5) Changes with depth, best at focus
6) smallest diameter crystal
7) largest diameter & highest frequency (least divergence)

35
Q

Focusing

A

concentrates the sound energy into a narrower beam and thus improves lateral resolution

36
Q

What are the three methods of focusing?

A

1) External focusing - with lens
2) Internal focusing - with curved active element
3) Phased array focusing - with the electronics of ultrasound system

37
Q

Internal and external focusing may be used with

A

single element transducers

38
Q

Phased array focusing is reserved specifically for

A

array tranducers those with multiple active elements

39
Q

Method Name. Type
1) Lens
2) Curved active element
3) Electronic

A

1) External: fixed, conventional, mechanical
2) Internal: fixed, conventional, mechanical
3) phased array adjustable type

40
Q

Fixed Focusing (Conventional or mechanical focusing) includes

A

both internal and external techniques

41
Q

With fixed focusing, the focal depth and the extent of focusing are determined when the transducer is

A

fabricated, and cannot be changed

42
Q

External focusing

A

a lens is placed in front of the piezoelectric material.
Ex: glasses

43
Q

External focusing:
As the arc of the lens becomes more _________, the degree of focusing ________ and the beam ________ in the focal zone.

A

prominent
increases
narrows

44
Q

Internal focusing

A

a curved piezoelectric crystal concentrates the sound energy into a narrower or tighter beam.
NO lens

45
Q

Internal focusing:
As the curvature of the PZT becomes more __________, the degree of focusing ________ .

A

pronounced
increases

46
Q

Internal focusing is the most _______ form of _____ _______

A

common
fixed
focusing

47
Q

Electric focusing

A

the system’s electronics focus the sound beam.

48
Q

Electric focusing:
With phased arrays, the sonographer can _____ the focusing characteristics of a beam.

A

adjust

49
Q

Electronic Focusing:
This technique may be used only on ___-___ _______ , never on _____ ______ ______.

A

multi-element transducers
single crystal transducers

50
Q

Phased array technology is _____ _____ than fixed focusing techniques.

A

more versatile

51
Q

Phased array means

A

adjustable or multiple focusing

52
Q

What happens to a beam when it is focused?

A

a sound beam undergoes four distinct modifications when focused

53
Q

4 Modifications of Focusing

A

1) Beam diameter in near field and focal zone is reduced
2) Focal depth is shallower
3) Beam diameter in the far zone increases
4) Focal zone is smaller

54
Q

Determinants of sound beams:
Characteristics Determined
Frequency-Continuous Wave

A

frequency of electrical signal from ultrasound system

55
Q

Determinants of sound beams:
Characteristics Determined
Frequency-Pulsed Wave

A

Thickness of ceramic and speed of sound in ceramic

56
Q

Determinants of sound beams:
Characteristics Determined
Focal length

A

Diameter of ceramic and frequency of sound

57
Q

Determinants of sound beams:
Characteristics Determined
Beam Divergence

A

diameter of ceramic and frequency of sound

58
Q

Determinants of sound beams:
Characteristics Determined
Lateral Resolution

A

Beam width

CMI 350 (11 decks)

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