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BDS3 Radiology > Q&A > Flashcards

Q&A Flashcards

1
Q

X-rays and visible light

A

are both forms of EM
Compared to visible light photos, X ray photons have
- Shorter wavelength, high frequency and higher energy

Some Same properties
- Weight, Speed, Etc

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2
Q

wavelength and frequency relation

A

inversely related

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3
Q

energy and frequency relation

A

are the same

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4
Q

During dental radiograph exposure, what is the primary type of interaction happening in the pt between X-ray photons and outer shell electrons

A

COMPTON

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5
Q

where are X-rays made in machine

A

filament

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6
Q

how are X-rays made

A

passing electron current through wire – jump from atom to atom
cloud of electrons collect around wire – thermionic

electrons and light released

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7
Q

between cathode and anode

A

high voltage
- Accelerated to huge speed due to positive speed and collide with black area target
(Tungsten)

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8
Q

direction of X-ray photons released from Tungsten target

A

all directions

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9
Q

result of X-ray photons being released in all directions from Tungsten target

A

Low energy absorbed by Al

Too divergent – hit side of spacer cone

Only right direction and right energy reach patient

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10
Q

continuous and characteristic spectrum interaction

A

Occur in x ray tube

Electron interacting with atom at target (tungsten)

Aim to lead to production of X-ray photons

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11
Q

photoelectric and Compton effect

A

Occur in pt

X-ray photons interacting with atom in tissue

Leads to attenuation of X-ray beam

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12
Q

continuous spectrum target interaction

A

Incoming electron passes close to target nucleus in Tungsten target, causing it to be rapidly slowed down and deflected

  • Lost kinetic energy released as photons
  • Closeness to nucleus determines degree deflected

Energy of photon can be anything between 0eV and the energy of the original electron

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13
Q

characteristic spectrum target interaction

A

Incoming electron collides with an inner-shell electron and either displaces it into a more peripheral shell (excitation) or removes it completely (ionisation)
- Reshuffle to fill space in inner most shell

Energy of photon can only be specific values characteristic of that tissue
- Jump difference between higher and lower shell

Characteristic to atom e.g. Tungsten

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14
Q

photoelectric effect

A

in pt tissues

Involves inner shell electrons

Results in complete absorption of x ray photon

Energy of incoming photon must be equal to or just greater than the binding energy of the electron

Contributes to image contrast and patient dose

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15
Q

compton effect

A

in pt tissues

Involves outer shell electrons

Results in scatter and partial absorption of photon

Energy of the incoming photon is much greater than the binding energy of electron

Contributes to pt dose

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16
Q

grading of radiographs (3 levels)

A

1 - excellent

2 - diagnostically acceptable

3 - unacceptable

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17
Q

excellent Grade 1 radiographs

A

no errors of pt preparation , exposure, positioning, processing or film handling

target - more than or = 70%

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18
Q

diagnostically acceptable Grade 2 radiographs

A

some errors of pt preparation, positioning, processing or film handling, but which do not detract from the diagnostic utility of the radiograph

target - less than or = 20%

19
Q

unacceptable Grade 3 radiographs

A

errors of patient preparation, exposure, positioning, or film handling, which render the radiograph diagnostically unacceptable

target - less than 10%

20
Q

reject analysis

A

needs to be carried out as well

21
Q

why may a radiograph be too dark

A

overexposed or underdeveloped so grade 3

22
Q

If a person stands 2m from an X-ray source absorbed 20uSv

how many received at 4m?

A

5uSv

23
Q

further away from X ray source means

A

lower dose

24
Q

inverse square law for X-ray intensity

A

Twice as far away quarter dose

Double distance = Quarter dose

25
Q

How far away should you be from X-ray source and pt when exposing a dental radiograph (< or = 70kV)

A

1.5m at least

From source and pt (Compton effect scatter)

Never stand in direct line of pt X-ray beam

In a small room treat whole room as controlled area
- Stand out of door

26
Q

Grays measure

A

absorbed dose

27
Q

Sieverts (Sv) measure

A

effective dose and equivalent dose

28
Q

absorbed dose (D)

A

measure of the amount of energy absorbed from the radiation beam per unit mass

medical exposures values often in mGy (x10^-3)

29
Q

equivalent dose (H)

A

takes into accoutn the radiobiological effectiveness of different types of radiation

equivalent dose = absorbed dose X radiation weighting factor

30
Q

radiation weighting Factor

X-ray and gamma photons+

Beta particles=

Alpha particles=

A

1

1

20

31
Q

effect dose (E)

A

takes into account the radio-sensitivities of different types of tissue
- some body parts are more sensitive to radiation than others

this allows for different investigations irradiating different parts of the body to be compared, by converting all doses to the equivalent whole body dose

uses a tissue weighting factor

32
Q

tissue weighting factors trend

A

higher the number = the more sensitive the tissue

33
Q

tissue weighting factors

gonads = 
red bone marrow = 
breast = 
thyroid gland = 
bone surface = 
skin =
A 
gonads = 0.20
red bone marrow = 0.12
breast = 0.05
thyroid gland = 0.05
bone surface = 0.01
skin = 0.01

also Brain not that sensitive but thyroid gland is more sensitive

34
Q

pregnancy and dental radiographs

A

No problem taking dental radiographs in 1st trimester

May delay for emotional/psychological reasons

35
Q

effective dose and risk

A

more likely to die from periapical than win the lottery
- 1 in 10 million compared to 1 in 47 million
Perspectives of risk

1 in 1 million risk

  • CBCT impacted molar
  • panoramic

<1 in 5 million risk

  • maxillary occlusal
  • periapical/bitewing

1 in 125,000 risk

  • transatlantic flight x 2
  • 100g brazil nuts
36
Q

radiosensitivity and age

A

younger pts more radiosensitive since cells dividing more rapidly

longer lifespan = more time for effects to develop

37
Q

age groups multiplication factor for risk

<10

A

x 3

38
Q

age groups multiplication factor for risk

10-20

A

x2

39
Q

age groups multiplication factor for risk

20-30

A

x 1.5

40
Q

age groups multiplication factor for risk

30-50

A

x 0.5

41
Q

age groups multiplication factor for risk

50- 80

A

x 0.3

42
Q

age groups multiplication factor for risk

> 80

A

negligible risk

43
Q

skin focus distance for correct magnification and dose of radiation

A

needs to be 20cm from source

BDS3 Radiology (14 decks)

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