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KCS: Theme 8 > Radiographic Image and Technique > Flashcards

Radiographic Image and Technique Flashcards

1
Q

X-ray interacts with … and this allows recording

A

matter

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2
Q

What’s inside an x-ray?

A
  • oil for cooling
  • transformers
  • tube
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3
Q

Define ‘beam quality’

A
  • related to the energy and penetration of the beam
  • KV setting (KV affects contrast)
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4
Q

Define ‘beam quantity’

A
  • related to the intensity of the photons exiting the tube
  • mA/current affects quality
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5
Q

KV impacts … and …
If there’s a high KV, image will be …

A
  • contrast and skin dose
  • dark
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6
Q

What is the usual KVp?
Why?

A
  • 70
  • reduces skin dose
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7
Q

What happens when you increase current and time?

A
  • more electrons
  • more x-ray photons
  • no change in energy
  • darker film
  • increases dose
  • aim is to increase the kVp, decrease mAs
  • payoff between dose and contrast
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8
Q

Define ‘image contrast’

A
  • difference in density between 2 adjacent structures
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9
Q

Define ‘image resolution’

A

also called clarity
- how small a structure can be resolved

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10
Q

What equipment looks at image contrast?

A
  • aluminium step wedge
  • assess develooper processor/film contrast
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11
Q

Image contrast is affected by …

A
  • Kv
  • developer temperature
  • use of intensifying screens
  • film fogging
  • scatter
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12
Q

Explain scatter

A
  • also known as secondary radiation
  • scatter degrades the image if it lands on receptor or film
  • only primary beam not deflected - contributes to image
  • scatter goes in all directions - forward scatter may degrade the image
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13
Q

What may look like scatter that isn’t scatter?

A
  • streak artefacts on CTs
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14
Q

How can you minimise scatter?

A
  • use collimators
  • and aiming devices
  • DPT or CBCT machine
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15
Q

How to reduce scatter reaching staff?

A
  • double distance
  • 1/4 the radiation dose
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16
Q

What is the control area in radiation protection?

A
  • inverse square law deems a controlled area
  • controlled area is anywhere in the primary beam and 1.5m from x-ray source
17
Q

3 ways x-ray may interact with matter

A
  • pass through
  • absorption
  • scattering
18
Q

Explain absorption of x-rays

A
  • photon is destroyed
  • it’s entire energy is transferred to target
19
Q

Explain scattering of x-rays

A
  • photon is deflected
  • transfers portion of its energy to the target - source of noise/fog
20
Q

What does absorption + scatter make?

A

attenuation of beam

21
Q

What forces do atoms have that mean they don’t collapse?

A
  • nuclear attractive force
  • centrifugal force
22
Q

5 interactions with matter

A
  • coherent scattering
  • comptom effect
  • photoelectric effect
  • pair production
  • photodisintegration
23
Q

Photoelectric absorption increases with …

A

Z
- atomic number

24
Q

Compton scattering increases with …

A
  • increasing KV
  • photon energy
25
Q

What is the photoelectric effect?

A
  • in the object
  • x-ray photon targets K-shell electrons in the atoms
  • x-ray photon transfers all energy to electron and energetic K shell electron is ejected
  • leaves vacancy in K shell
  • L shell electron fills vacancy in K shell
  • characteristic photon emitted
  • photon energy - difference in K and L shell electron energies
26
Q

Explain Compton scattering

A
  • photon hits free electron
  • photon has reduced energy and transfers energy to an energetic electron
  • photons having small deflections retains most incident energy
  • photons will scatter many times losing energy each time until energy is absorbed
27
Q

Features of dental film

A
  • waterproof and lightproof packet
  • lead foil (with pattern)
  • black paper
  • film
  • embossed dot
28
Q

How does air/soft tissue look on an x-ray?

A
  • lots of x-rays penetrate
  • expose many silver halide crystals
29
Q

How does bone look under x-ray?

A
  • less x-rays penetrate than air/tissue
  • fewer crystals exposed
30
Q

How does amalgam/gold look under x-ray?

A
  • few if any x-rays can penetrate
  • silver halide crystals not exposed
31
Q

What is the developing stage of film scientifically?

A
  • exposure centres in crystals are converted into black metallic silver
32
Q

How to stop having bulky sensors?

A
  • use CCD-based sensors
33
Q

How does a phosphor plate work?

A
  • conduction band with electron traps below it
  • x-rays are absorbed and you get a valence band
34
Q

Explain photo-stimulated luminescence

A
  • conduction band and red laser light at electron tags below
  • becomes blue light - get grouped electron tags
35
Q
A

KCS: Theme 8 (4 decks)

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