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BODC > IRMER > Flashcards

IRMER Flashcards

1
Q

What is the absorbed dose

A

Absorbed radiation per kg

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2
Q

What is the effective dose

A

The measure of risk. Whole body effective dose is 1 and then divided per risk per organ.

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3
Q

What is the dose equivalent

A

The measure of the harmfulness of the absorbed dose.

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4
Q

What are the units for the dose equivalent and effective dose

A

Sievert, Sv.

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5
Q

How does radiation affect DNA

A

Directly by knocking out an e- from the DNA or indirectly by creating free radicals from ionising water.

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6
Q

Stochastic effects

A

Increased dose doesn’t increase the severity of the effects but increases the probability of getting dose caused effects e.g. cancer. No threshold.

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7
Q

Deterministic effects

A

Increased dose = increased the severity of effects, when dose is above a threshold. The threshold is different for different tissues.

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8
Q

What safety measures can be used to reduce the dose or protect people from radiation

A

Reduce distance, reduce exposure time, use lead to shield, monitor radiation levels on staff and surrounding, have a controlled area (6mV).

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9
Q

What material/amount does it need to stop each radiation particle

A 
a = 1cm of air or 1 mm of matter
b = a few mm of aluminium
y = a few cms of lead
x-ray = a few cms of lead (less than for y)
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10
Q

Structure of an x-ray tube

A 
The cathode (-) releases e-
The anode (+) is hit by e- so needs to have a high mp and high atomic number/density to absorb the e-, e.g. tungsten, with a copper tube to absorb heat.
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11
Q

Rectification

A

AC becomes DC and x3. Negative waves flipped so twice as many and all positive and then everything x3.

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12
Q

Bremsstrahlung

A

When e- are rapidly decelerated by the atom’s +ve nucleus and lose lots of energy and release a photon. Different E of the photons depending on the number of protons in the atom. Continuous.

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13
Q

Measuring attenuation

A

I = Io x e^-ut
u is the liner attenuation coefficient
Io is the monoenergetic beam

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14
Q

What do all the radiation particles have an effect on

A

Fluorescent effect on phosphor screens and an effect on photographic film

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15
Q

Relationship between current and intensity and quality of the image

A

mA proportional to intensity

No change in quality of image

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16
Q

Relationship between voltage and intensity and quality of the image

A

Intensity is proportional to kVp^2

Increase voltage increases the quality of the image

17
Q

Relationship between z/atomic number of the target tissue and intensity and quality of the image

A

Intensity is proportional to Z

No change in the quality of the image

18
Q

Relationship between filtering and intensity and quality of the image

A

Intensity reduces, quality increased when filtering applied

19
Q

Relationship between rectifying and intensity and quality of the image

A

Rectifying the current increases the intensity and the quality of the image

20
Q

Details for filtration of the x-rays

A

Use 1.5mm of aluminium, absorbs the low energy photons that increase the dose but reduce the image quality. A legal requirement.

21
Q

What happens if u reduce the Voltage

A

Reduced transmission, increased dose, more attenuation, less Compton scattering, better contrast of the image.

22
Q

What happens if u increase the voltage

A

Higher energy photons so more transmission so a smaller dose (fewer photons absorbed by the body) and a better quality beam, but more Compton scattering and reduced contrast of the image.
Increased photoelectric effect.

23
Q

How can you increase the quality of the beam

A

Increase the voltage or add filtration

24
Q

How can you double the intensity/number of photons

A

Double the current

25
Q

Explain the photoelectric effect

A

High energy photons are absorbed by an e- in an atom. If the energy of the photon is higher than the electron binding energy, the electron is released (photoelectron)

26
Q

Structure of the film

A

Emulsion layer contains silver halide crystals.

27
Q

Structure of the screen

A

Reflective layer reflects the light photons back to the screen.
Phosphor screen where photoelectric effect happens, x-rays absorbed and more light photons emitted.
Film in the middle.

28
Q

How does the screen work

A

Phosphor screen converts x-rays into more light photons. These hit the screen and are absorbed and cause blackening. Interaction in the phosphor and photons spread out in all directions so when they hit the film they have spread out so the image is larger.

29
Q

Importance of matching up fluorescent materials to films

A

Different fluorescent materials produce different colours of light and different films are more sensitive to different colours of light.

30
Q

What is speed

A

Speed is the sensitivity of the film/amount of blackening of crystals.

31
Q

What factors does the speed depend on

A

Thickness of film
Size of crystals (bigger = more sensitive but reduced resolution)
The efficiency of conversion of x-rays to photons
Light absorbing dyes on the film - reduce speed but increase the resolution.
Speed is inversely proportional to the resolution.

32
Q

Latent image formation

A
  1. X-ray absorbed by silver halide and makes the halide release an e- which moves to a defect or impurity in the crystal = a sensitivity speck.
  2. e- attracts silver ions which become atoms and attract more e- and the process is repeated until small deposits of silver in crystals hit by x-rays.
  3. These deposits are more sensitive to the developer so get blackened more.
33
Q

Developing process

A
  1. Alkaline added which converts the rest of the silver ions into atoms. Crystals sensitised by the x-rays will be affected more.
  2. Washed off so that it doesn’t neutralise the acid and to stop the alkaline from acting and blackening all the film.
  3. Acid added to harden the image and remove unreacted silver halide.
  4. Washed off to prevent staining
34
Q

Latent image fading

A

When some silver atoms converted back to ions

35
Q

Factors affecting the subject contrast

A

Voltage of tube
Contrasting agents e.g. iodine
Grids stop scattering

36
Q

Factors affecting film contrast

A

Optical density e.g. 1 = 10% of light transmitted, 2 = 1% of light.

37
Q

How does the latitude of dose/optical density graph affect the image

A

Wider latitude = a range of doses with the same optical density/blackening so reduced contrast

38
Q

What is film fog and how do you reduce it

A

Blackening due to background/natural sources. Reduce by keeping the film in a cold dark room away from radiation sources.

BODC (4 decks)

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