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MED 107- MEDICAL PHYSICS II > 78. ULTRASOUNDS: RESOLUTION > Flashcards

78. ULTRASOUNDS: RESOLUTION Flashcards

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1
Q
  1. What does the Spatial Resolution of an Ultrasound device determine?
A
  • it determines the ability to separate two adjacent
    objects
  • it allows us to differentiate between 2 objects that are
    very close together
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2
Q
  1. What 3 planes do we consider Spatial Resolution in?
A
  1. Depth (Axial) Resolution
  2. Lateral Resolution
  3. Elevation Resolution
    - this is the height of the slice
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3
Q
  1. What do these Test images of phantoms show?
A
  • they show circular regions
  • they are echo free
  • they mimic the presence of cysts of varying sizes
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4
Q
  1. What are the diameters of these circular, echo free regions?
A
  • 10 mm
  • 8 mm
    -6 mm
    -4 mm
    -3 mm
    -2 mm
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5
Q
  1. What is the relation between the holes and the frequency?
A

LOW FREQUENCY TRANSDUCERS
- have more echo free holes
- they also have a larger focal length

HIGH FREQUENCY TRANSDUCERS
- have less echo free holes
- they also have a shorter focal length
- they also have a better resolution
- we can define the echo free regions better

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6
Q
  1. What 2 concerns must be balanced when we set the frequency for Ultrasound imaging?
A
  1. The depth to which the image will be formed
  2. The Spatial resolution of the image
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7
Q
  1. What do we use lower frequency waves to image?
A
  • they image deep within the abdomen
  • this is because they have longer wavelengths
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8
Q
  1. What do we use higher frequency waves to image?
A
  • they image finer details that can be resolved
  • the parts of the body they image are close to the
    surface
  • this is because they have shorter wavelengths
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9
Q
  1. What other body part can higher frequency waves image?
A
  • they can be used for Breast ultrasounds
  • these are about 7.5-10 MHz

THIS IS BECAUSE:
- much shallower regions of the body must be imaged
in the latter procedure

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10
Q
  1. What other advantage do high frequency sound waves bring about?
A
  • they have a higher spatial resolution
  • this helps with introducing the transducer into the
    body near the tissues to be imaged
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11
Q
  1. What does Axial Resolution determine?
A
  • it determines the ability to separate two objects that
    are lying along the axis of the beam
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12
Q
  1. What does Axial Resolution tell us about?
A
  • it tells us about the minimum distance that two
    structures can be away from each other
  • while still producing two distinct echos on an image

THESE STRUCTURES:
- are positioned front to back

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13
Q
  1. What is Axial Resolution determined by?
A
  • it is determined by the pulse length
  • it is measured in mm
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14
Q
  1. What is the Pulse Length?
A
  • this is the wavelength
    MULTIPLIED BY
  • the number of cycles in the pulse
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15
Q
  1. What do lower numerical values of the Axial Resolution indicate?
A
  • they indicate a shorter pulse
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16
Q
  1. What kind of images do shorter pulses create?
A
  • they create more accurate images
17
Q
  1. What kind of Axial Resolution results in a better image quality?
A
  • Axial Resolutions that have a lower numerical value
18
Q
  1. How do we mathematically describe Axial Resolution?
A
19
Q
  1. How do we calculate Pulse Length?
A
20
Q
  1. What are some characteristics Higher Frequency?
A
  • they have a lower axial resolution
21
Q
  1. What relation do wavelength and frequency have to one another?
A
  • they are inversely proportional
22
Q
  1. What relation do the number of cycles in a pulse and the frequency have to one another?
A
  • they are inversely proportional
23
Q
  1. What echo and interface distances produce a better Axial Resolution?
A

THERE WILL BE A BETTER RESOLUTION:
- when there is a smaller distance between the echos
- larger distances between the interfaces

THIS MEANS THAT THE:
- signals will be more clear
- the values and signals are discrete

24
Q
  1. What echo and interface distances produces a lower Axial Resolution?
A

THERE WILL BE A LOWER RESOLUTION:
- when there is a larger distance between the echos
- smaller distances between the interfaces

THIS MEANS THAT THE:
- signals will combine
- the transducer will receive signals that are very close
together
- this worsens the resolution

MED 107- MEDICAL PHYSICS II (108 decks)

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