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Ultrasound Physics > Chapter 10 Axial and Lateral Resolution > Flashcards

Chapter 10 Axial and Lateral Resolution Flashcards

0
Q

The ability to distinguish two structures lying close together front-to-back or parallel to the sound beam is called?

A

Longitudinal, Axial, Range, Radial, or depth resolution

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1
Q

Accuracy in imaging is called what?

A

Resolution

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2
Q

What are the units of axial resolution?

A

Measured in mm or any other unit of distance

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3
Q

Axial resolution is related to what?

A

Spatial pulse length

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4
Q

Synonyms for axial resolution?

A 
LARRD:
Longitudinal
Axial
Range
Radial
Depth
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5
Q

The sonographer _________ change axial resolution?

A

Cannot

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6
Q

In clinical imaging, axial resolution ranges from _____ to _____mm.

A

0.1 to 1.0 mm

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7
Q

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

A

The image quality is better when axial resolution has a lower numerical value.

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8
Q

Lower numerical values of axial resolution indicate?

A

Shorter pulse

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9
Q

Shorter pulses create more ___________ images?

A

Accurate

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10
Q

What is the mathematical description of axial resolution?

A

Axial resolution(mm) = spatial pulse length (mm)/2

Axial resolution (mm) = (wavelength (mm) * # of cycles in pulse)/2

In soft tissue: 
Axial resolution (mm) = (0.77 * # of cycles in pulse)/ frequency (MHz)
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11
Q

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

A

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

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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

A pulse is short if there are few cycles in the pulse, just like a train is short if there are few cars in the train. This is known as?

A

Less ringing

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14
Q

What is one way to reduce ringing?

A

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

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15
Q

A pulse is short if each cycle in the pulse has a __________ wavelength.

A

Short

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16
Q

Shorter wavelengths are characteristics of _____________.

A

Higher frequency sound

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17
Q

Pulses made of higher frequency cycles have ____________ axial resolution.

18
Q

Better axial resolution is associated with the following:

A
  • shorter spatial pulse length
  • shorter pulse duration
  • higher frequencies (shorter wavelengths)
  • fewer cycles per pulse (less ringing)
  • lower numerical values
19
Q 
Which of the following transducers has the poorest axial resolution? 
A. 1.7 MHz and 4 cycles/pulse
B. 2.6 MHz and 3 cycles/pulse
C. 1.7 MHz and 5 cycles/pulse
D. 2.6 MHz and 2 cycles/pulse
A

C. This is the longest pulse. It has the lowest frequency and the most ringing (more cycles/pulse)

20
Q

Axial resolution is ________ in transducers with the highest frequency and the fewest numbers of cycles per pulse.

21
Q

The ability to distinctly identify two structures that are very close together when the structures are side-by-side, or perpendicular to the beams main axis

A

Lateral resolution

22
Q

This answers the question: what is the minimum distance that two structures, positioned side-by-side, can be apart and still produce two distinct echoes on an ultrasound image?

A

Lateral resolution

23
Q

What are the units for lateral resolution?

A

Units of mm, cm, or any unit of distance

24
Q

Lateral resolution is determined by?

A

Width of the sound beam

25
Q

Narrower beams have ______ resolution.

26
Q

How does a sonographer improve image resolution?

A

Adjust depth; beam diameter varies with depth

27
Q

Synonyms for lateral resolution?

A 
LATA: 
Lateral
Angular
Transverse
Azimuthal
28
Q

Lateral resolution is best at the ______.

29
Q

The mathematical relationship for lateral resolution is?

A

Lateral resolution (mm) = beam diameter (mm)

30
Q

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

A

Axial resolution because pulses are shorter than they are wide

31
Q

When two reflectors are closer side-by-side than the beam width, what will be observed?

A

One reflector

32
Q

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

A

Axial resolution is improved due to its shorter pulses

Lateral resolution is improved due to its pulses diverging less in the far field

33
Q

What are the three methods of focusing?

A
  1. External focusing - with a lens
  2. Internal focusing - with a curved active element
  3. Phased array focusing - with the electronics of the ultrasound system
34
Q

Which focusing technique(s) can be used with single element transducers? Array transducers?

A

Single element transducers = external and internal focusing

Array transducers = phased array focusing

35
Q

External and internal focusing techniques are both called what?

A

Fixed focusing
Conventional focusing
Mechanical focusing

36
Q

What is a limitation to fixed focusing?

A

Focal depth and the extent of focusing cannot be changed

37
Q

What four things happen to a beam when it is focused?

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
38
Q

In regards to sound beams, continuous wave frequency is determined by?

A

Electrical frequency from ultrasound system

39
Q

In regards to sound beams, pulsed wave frequency is determined by?

A

Thickness of ceramic and speed of sound in ceramic

40
Q

In regards to sound beams, focal length is determined by?

A

Diameter of ceramic and frequency of sound

41
Q

In regards to sound beams, beam divergence is determined by?

A

Diameter of ceramic and frequency of sound

42
Q

In regards to sound beams, lateral resolution is determined by?

A

Beam width

Ultrasound Physics (7 decks)

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