Radiographic Image and Technique

Question 1

X-ray interacts with … and this allows recording

Answer 1

matter

Question 2

What’s inside an x-ray?

Answer 2

• oil for cooling
• transformers
• tube

Question 3

Define ‘beam quality’

Answer 3

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

Question 4

Define ‘beam quantity’

Answer 4

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

Question 5

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

Answer 5

• contrast and skin dose
• dark

Question 6

What is the usual KVp?
Why?

Answer 6

• 70
• reduces skin dose

Question 7

What happens when you increase current and time?

Answer 7

• 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

Question 8

Define ‘image contrast’

Answer 8

• difference in density between 2 adjacent structures

Question 9

Define ‘image resolution’

Answer 9

also called clarity
- how small a structure can be resolved

Question 10

What equipment looks at image contrast?

Answer 10

• aluminium step wedge
• assess develooper processor/film contrast

Question 11

Image contrast is affected by …

Answer 11

• Kv
• developer temperature
• use of intensifying screens
• film fogging
• scatter

Question 12

Explain scatter

Answer 12

• 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

Question 13

What may look like scatter that isn’t scatter?

Answer 13

• streak artefacts on CTs

Question 14

How can you minimise scatter?

Answer 14

• use collimators
• and aiming devices
• DPT or CBCT machine

Question 15

How to reduce scatter reaching staff?

Answer 15

• double distance
• 1/4 the radiation dose

Question 16

What is the control area in radiation protection?

Answer 16

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

Question 17

3 ways x-ray may interact with matter

Answer 17

• pass through
• absorption
• scattering

Question 18

Explain absorption of x-rays

Answer 18

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

Question 19

Explain scattering of x-rays

Answer 19

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

Question 20

What does absorption + scatter make?

Answer 20

attenuation of beam

Question 21

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

Answer 21

• nuclear attractive force
• centrifugal force

Question 22

5 interactions with matter

Answer 22

• coherent scattering
• comptom effect
• photoelectric effect
• pair production
• photodisintegration

Question 23

Photoelectric absorption increases with …

Answer 23

Z
- atomic number

Question 24

Compton scattering increases with …

Answer 24

• increasing KV
• photon energy

Question 25

What is the photoelectric effect?

Answer 25

- 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

Question 26

Explain Compton scattering

Answer 26

- 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

Question 27

Features of dental film

Answer 27

- waterproof and lightproof packet - lead foil (with pattern) - black paper - film - embossed dot

Question 28

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

Answer 28

- lots of x-rays penetrate - expose many silver halide crystals

Question 29

How does bone look under x-ray?

Answer 29

- less x-rays penetrate than air/tissue - fewer crystals exposed

Question 30

How does amalgam/gold look under x-ray?

Answer 30

- few if any x-rays can penetrate - silver halide crystals not exposed

Question 31

What is the developing stage of film scientifically?

Answer 31

- exposure centres in crystals are converted into black metallic silver

Question 32

How to stop having bulky sensors?

Answer 32

- use CCD-based sensors

Question 33

How does a phosphor plate work?

Answer 33

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

Question 34

Explain photo-stimulated luminescence

Answer 34

- conduction band and red laser light at electron tags below - becomes blue light - get grouped electron tags