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BDS3 exam prep > Radiology > Flashcards

Radiology Flashcards

1
Q

how are x-rays produced?

A

when high energy electrons collide with matter

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2
Q

what are properties of x-rays

A
  1. electromagnetic radiation
  2. high energy
  3. ionising radiation
  4. short wavelength
  5. absorption
  6. fluorescence
  7. scattering
    8 They travel in a straight line and do not carry an electric charge with them.
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3
Q

what is a ghost image

A

a secondary image that is produced due to scattering

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4
Q

what are properties of ghost image?

A
  1. reduced contrast
  2. shifted position
  3. lower resolution
  4. faint appearance
  5. repetitive pattern
  6. reduced diagnostic quality
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5
Q

what is scattering

A

when x-ray photons interact with matter and it changes direction

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6
Q

what shape are collimators used and why?

A

Rectangular - this is because it can reduce surface area being irradiated by almost 50%

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7
Q

what are the sizes of collimators used?

A

preferably < 45mm x 35mm
and no greater than 60mm diameter circular beam

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8
Q

how do we reduce dose?

A
  1. optimisation of exposure parameters
  2. use of collimation
  3. shielding
  4. use of digital radiology
  5. dose tracking
  6. image processing software
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9
Q

what happens when the patient is too far or too close from the x-ray source?

A
  1. image distortion
  2. reduced radiation
  3. increased radiation exposure
  4. longer exposure times
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10
Q

characteristics of a ghost image

A
  1. always appears higher due to the -ve vertical beam angulation
  2. always horizontally magnified
  3. change in antero-posterior position
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11
Q

describe the process of Compton Scatter

A
  • the x ray photon interacts with an outer shell electron
  • the x ray photon has considerably greater energy than the electron binding energy and because of this a lot of energy will be left in the photon
  • following the collision, the photon has lower energy and is referred to as a scatter photon
  • it then undergoes a change in direction depending on how much energy it lost
  • the scatter photon can then go on to be involved in other Compton or photoelectric interactions
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12
Q

how does Compton scatter differ from Photoelectric effect

A
  • the x ray photon is completely absorbed by the electron it collides with, whereas in Compton effect the x ray photon ‘bounces off’ the electron
  • photoelectric absorptions only occur when the energy of the x ray photon is slightly greater than the binding energy of the electron.
  • however, in Compton effect the energy of the x ray production is considerably higher than the energy of the electron
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13
Q

What metal is used to absorb the heat generated during x-ray production

A

copper

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14
Q

Name another metal used in x-ray production

A

Tungsten
Aluminium

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15
Q

what is the horizontal line for OPT parallel to floor

A

Frankfurt Plane
(lower border of orbit to the upper border of the external auditory meatus)

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16
Q

main components of the tubehead

A

X-ray tube
Metal shielding
- Usually lead, Absorbs X-rays, Window where X-ray beam exits
Aluminium filtration
Oil
Dissipates heat produced by X-ray tube by thermal convection
Spacer cone

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17
Q

what 3 ways can photons interact with matter

A
  1. transmission (passes through unaltered)
  2. absorption (stopped by matter)
  3. scatter (changes direction)
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18
Q

what is attenuation

A

reduction in intensity of x-ray beam

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19
Q

what are the 2 specific attenuation interactions

A
  1. Photoelectric effect - complete absorption
  2. Compton effect - partial absorption & scatter
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20
Q

what is forward scatter

A

when higher energy photons are deflected more forward

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21
Q

what is back scatter

A

when lower energy photons are deflected more backward

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22
Q

How do you reduce scatter?

A

Collimation

  1. decrease surface area irradiated
  2. decreases volume of irradiated tissue
  3. decreases number of scattered photons produced in the tissue
  4. decreases photons interacting with receptor
  5. decreases loss of contrast on radiographic image
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23
Q

how does the photoelectric effect impact on radiation dose

A

deposition of all x ray photons into tissue means increases patient dose but it is necessary for image production

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24
Q

how does compton effect affect radiation dose

A

deposition of some x-ray photon energy in tissue means increased patient dose but scatter photons do not contribute usefully to image, may increase dose to operators (back scatter)

25
Q

what is the effect of lowering kV on x-ray unit

A

overall lower energy photons produced
increases photoelectric effect interactions
increases contrast between tissues with different Z
increases dose absorbed by patient

26
Q

what is the effect of raising kV on x-ray unit

A

overall higher energy photons produced
decreases photoelectric effect interactions (increase forward scatter)
decreases dose absorbed by patient

27
Q

what is the suitable range of kV for intraoral x-ray units

A

60-70kV

28
Q

what are the principles of medical ionising radiation

A

ALARA: “As Low As Reasonably Achievable”.

Justification - potential benefits to the patient from the procedure should outweigh the potential risks of radiation exposure.

Optimization: ensure that the dose is appropriate for the diagnostic task and that the image quality is adequate for purpose

Dose Limits: The exposure of patients and medical personnel to ionising radiation should be kept below dose limits

Time, Distance, and Shielding: The principles of time, distance, and shielding should be used to minimise radiation exposure.

29
Q

what happens when radiation passes through matter

A

it ionises atoms along it’s path
each ionisation process will deposit a certain amount of energy locally (approx 35eV)

30
Q

what is a significant effect of ionising radiation

A

DNA damage

31
Q

how does radiation cause DNA damage - direct effect

A

radiation interacts with the atoms of a DNA molecule or another important part of the cell

32
Q

how does radiation cause DNA damage - INdirect effect

A

radiation interacts with water in the cell, producing free radicals which are unstable and highly reactive molecules

33
Q

Radiosensitivity of tissues is dependent on what 2 factors

A
  1. the function of the cells that make up the tissues
  2. if the cells are actively dividing
34
Q

what are highly radiosensitive tissues and why

A

bone marrow, lymphoid tissues, GI, gonads, embryonic tissues

this is because the more rapidly a cell is dividing, the greater the sensitivity to radiation

35
Q

what are the possible outcomes after radiation hits a cell nucleus

A
  1. no change
  2. DNA mutation
    - mutation repaired –> viable cell
    - cell death –> unviable cell
    - cell survives but is mutated –> cancer?
36
Q

what is dose

A

it is a measure of the amount of energy that has been transferred and deposited in a medium

37
Q

what is absorbed dose

A

measures the energy deposited by radiation and has units of Gray (Gy)

38
Q

what is equivalent dose

A

absorbed dose multiplied by a weighting factor depending on the type of radiation

39
Q

what is the LNT model

A

it estimates the long term biological damage from radiation.
it assumes the damage is directly proportion to radiation dose and that radiation is always harmful with no safety threshold

40
Q

what are the 2 types of biological effects of radiation on the population

A

deterministic effects
stochastic effects

41
Q

effect of radiation during pregnancy

A

early pregnancy
cancer incidence in children

42
Q

what are lateral cephalograms

A

The X-ray beam is perpendicular to the receptor and the patient’s mid-sagittal plane

43
Q

For conventional cephalogram units, why is there a relatively large distance (1.5km+) between the x-ray source and the receptor?

A

to reduce asymmetrical magnification of anatomy

44
Q

The patient often wears lead protection to protect what?

A

Thyroid gland (it is radiosensitive, susceptible to damage)

45
Q

Why is the cephalostat (i.e. head positioning apparatus) important?

A

for reproducibility, always in exact same position

46
Q

clinical applications of cephalometry

A

orthodontics and orthognathic surgery
used to monitor change

47
Q

what is a oblique lateral radiograph

A

provides view of posterior jaws without superimposition of contralateral side

48
Q

indications of taking a oblique lateral radiograph

A

assessment of dental pathology
assessment of presence/position of unerupted teeth
detection of mandibular fractures
evaluating lesions/conditions affecting jaws

49
Q

what is parallax

A

an apparent change in the position of an object caused by a real change in the position of the observer

50
Q

Parallax mnemonic

A

same
lingual
opposite
buccal

51
Q

aim of Quality assurance of clinical image quality

A

to ensure your radiographs are consistently diagnostic and that you patient are not exposed to unnecessary radiation

consists of 3 parts
1. image quality rating
2. image quality analysis
3. reject analysis

52
Q

what are the 3 digital image receptor checks

A
  1. the receptor
    - check for visible damage
    - check if clean
  2. image uniformity
    - expose receptor to an an unattenuated x-ray beam and check if resulting image is uniform
  3. image quality
    - take a radiograph of a test object and assess the resulting image against a baseline
53
Q

what are potential faults visible on image

A

collimation error (cone cutting)
incorrect image radiodensity (too dark/light)

54
Q

glass envelope?

A

vacuum
makes sure x-rays travel in desired direction

55
Q

focal spot angulation

A

increases heat tolerance
reduces pnumbra effect

56
Q

min distance of spacer cone

A

200mm

57
Q

focussing cup

A

metal plate that surrounds filament (-vely charged)
when electron leave the filament sends them to anode

58
Q

Pnumbra effect

A

focal spot not in single point
blurring of image

59
Q

x ray production needs unidirectional current - how is this achieved?

A

via transformers (cathode anode + filament)
by a process called rectification

BDS3 exam prep (13 decks)

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