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Ultrasound Physics > Week 9 Axial and Lateral Resolution > Flashcards

Week 9 Axial and Lateral Resolution Flashcards

Axial and Lateral Resolution

1
Q

Resolution

A

The ability to create accurate images.

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2
Q

What is Axial Resolution?

A

The ability of a system to display 2 structures that are close together when structures are parallel to the sound beams main axis.

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3
Q

What is axial resolution measured in?

A

distance, mm

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4
Q

What is axial resolution determined by?

A

It is determined by spatial pulse length.

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5
Q

What is the typical value of axial resolution?

A

0.1 to 1.0 mm

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6
Q

Other names for axial resolution

A

LARRD:
Longitudinal
Axial
Range
Radial
Depth

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7
Q

Is axial resolution adjustable by the sonographer?

A

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

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8
Q

Which is better for axial resolution, short or long pulses?

A

Short pulses improve axial resolution.

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9
Q

Shorter pulse lengths Improves what?

A

The ability to accurately portray structures.

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10
Q

Pulse duration

A

Is related to axial resolution.

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11
Q

axial resolution formula in soft tissue:

A

AR = 0.77 x # of cycles/ frequency

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12
Q

Better axial resolution is associated with:

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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12
Q

How is a shorter pulse created?

A
  1. Less ringing
  2. Higher frequency
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13
Q

If there are more cycles in a pulse, the numerical value of range resolution is
greater, lesser or same?

A

greater

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14
Q

If a new pulsed transducer has many more cycles in its pulse, the image accuracy improves, degrades or remains the same?

A

it Degrades

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15
Q

High/ Low frequency transducers generally have the best range resolution?

A

High

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16
Q

Axial resolution formula:

A

spatial pulse length (mm) / 2

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17
Q

In soft tissue, a 3 cycle 1 MHz pulse has a pulse length equal to 4.5 mm. what is the axial resolution?

A

2.25

Axial resolution is 1/2 of the spatial pulse length.
4.5 / 2 = 2.25

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18
Q

Which of the following transducers have the best axial resolution?

A. 1.7 MHz & 4 cycles/ pulses
B. 2.6 MHz & 3 cycles/ pulses
C. 1.7 MHz & 5 cycles/ pulses
D. 2.6 MHz & 2 cycles/ pulses

A

D. 2.6 MHz & 2 cycles/ pulses

High frequency
Low ringing ( fewest cycles/ pulses)

19
Q

Which of the following transducers has the poorest axial resolution?

A. 1.7 MHz & 4 cycles/ pulses
B. 2.6 MHz & 3 cycles/ pulses
C. 1.7 MHz & 5 cycles/ pulses
D. 2.6 MHz & 2 cycles/ pulses

A

C. 1.7 MHz & 5 cycles/ pulses

Low frequency
Long ringing ( longest cycles/ pulses)

20
Q

What is Lateral resolution?

A

The ability to identify 2 structures that are close together when they are side by side or perpendicular to the sound beam.

21
Q

What is lateral resolution determined by?

A

It is determined by the width of the beam.

22
Q

What are other names for Lateral resolution?

A

LATA:
Lateral
Angular
Transverse
Azimuthal

23
Q

What area of the beam produce the best lateral resolution?

A

The focal zone, or the narrowest part of the beam.

24
Q

Axial numbers will be bigger or smaller than lateral resolution?

A

smaller than lateral resolution.

25
Q

Lateral resolution improves or degrades in the far field?

A

Improves in the far field.

26
Q

Why does lateral resolution improve in the far field?

A

High frequency creates a deeper focus than low frequency.

27
Q

Does lateral resolution change or stay the same with depth?

A

Changes with depth, best at focus.

28
Q

In the near field, lateral resolution is best with?

A

smallest diameter crystal

29
Q

In the far field, lateral resolution is best with?

A

Large diameter and highest frequency.
( least divergence)

30
Q

What are the effects of focusing?

A
  1. beam diameter in near field and focal zone is reduced.
  2. Focal depth is shallow
  3. Beam diameter in the far zone increases.
  4. Focal zone is smaller
31
Q

Focusing improves what?

A

Lateral resolution

32
Q

What are the three methods of focusing?

A
  1. External focusing
  2. Internal
  3. Phased Array
33
Q

What method of focusing do we use in ultrasound?

A

Phased Array

34
Q

External focusing

A

lens is placed in front of the PZT.
fixed, conventional, or mechanical.

35
Q

Curved element

A

internal lens
Fixed, conventional, or mechanical

36
Q

Phased Array

A

Electronic Focusing

37
Q

Is Phased array able to be adjusted by the sonographer?

A

Yes

38
Q

In regard to axial resolution, lower numerical values indicate what?

A

shorter pulses and improved axial resolution.

39
Q

Two different transducers create pulses. both transducers create sound with a freq. of 4MHz. One transducer creates a pulse that comprises 6 cycles and the other, 3 cycles. Which transducer is more likely to create a more accurate image with respect to axial resolution? Which transducer has a lower numerical value of axial resolution?

A

3 cycle pulse is more likely to create an image with better axial resolution. Less ringing, or fewer cycles in a pulse, generally implies shorter pulses and improved axial resolution.

40
Q

Two different transducers create sound pulses. One transducer is labeled 5 MHz and the other, 3 MHz. Which transducer is more likely to create a more accurate image with respect to axial resolution? Which transducer probably has a lower numerical value of axial resolution?

A

The 5 MHz transducer is more likely to create an image with better axial resolution. The Higher frequency transducer creates a shorter pulse and thus has a lower numerical value of axial res.

41
Q

what is the mathematical relationship that describes this beam diameter and lateral resolution?

A

lateral resolution = beam diameter

42
Q

What type of focusing includes both external and internal techniques?

A

Fixed focusing

43
Q

A lens is placed where on the transducer with external focusing? What type of focusing is this?

A

In front of the PZT, a fixed focusing technique for external focusing.

44
Q

What does a curved PZT do to the beam? What type of focusing is this?

A

Concentrates the sound energy into a narrower or tighter beam. Internal focusing.

Ultrasound Physics (10 decks)

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