IRMER

Question 1

What is the absorbed dose

Answer 1

Absorbed radiation per kg

Question 2

What is the effective dose

Answer 2

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

Question 3

What is the dose equivalent

Answer 3

The measure of the harmfulness of the absorbed dose.

Question 4

What are the units for the dose equivalent and effective dose

Answer 4

Sievert, Sv.

Question 5

How does radiation affect DNA

Answer 5

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

Question 6

Stochastic effects

Answer 6

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

Question 7

Deterministic effects

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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)

Question 10

Structure of an x-ray tube

Answer 10

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.

Question 11

Rectification

Answer 11

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

Question 12

Bremsstrahlung

Answer 12

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.

Question 13

Measuring attenuation

Answer 13

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

Question 14

What do all the radiation particles have an effect on

Answer 14

Fluorescent effect on phosphor screens and an effect on photographic film

Question 15

Relationship between current and intensity and quality of the image

Answer 15

mA proportional to intensity

No change in quality of image

Question 16

Relationship between voltage and intensity and quality of the image

Answer 16

Intensity is proportional to kVp^2

Increase voltage increases the quality of the image

Question 17

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

Answer 17

Intensity is proportional to Z

No change in the quality of the image

Question 18

Relationship between filtering and intensity and quality of the image

Answer 18

Intensity reduces, quality increased when filtering applied

Question 19

Relationship between rectifying and intensity and quality of the image

Answer 19

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

Question 20

Details for filtration of the x-rays

Answer 20

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

Question 21

What happens if u reduce the Voltage

Answer 21

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

Question 22

What happens if u increase the voltage

Answer 22

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.

Question 23

How can you increase the quality of the beam

Answer 23

Increase the voltage or add filtration

Question 24

How can you double the intensity/number of photons

Answer 24

Double the current

Question 25

Explain the photoelectric effect

Answer 25

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)

Question 26

Structure of the film

Answer 26

Emulsion layer contains silver halide crystals.

Question 27

Structure of the screen

Answer 27

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.

Question 28

How does the screen work

Answer 28

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.

Question 29

Importance of matching up fluorescent materials to films

Answer 29

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

Question 30

What is speed

Answer 30

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

Question 31

What factors does the speed depend on

Answer 31

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.

Question 32

Latent image formation

Answer 32

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.

Question 33

Developing process

Answer 33

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

Question 34

Latent image fading

Answer 34

When some silver atoms converted back to ions

Question 35

Factors affecting the subject contrast

Answer 35

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

Question 36

Factors affecting film contrast

Answer 36

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

Question 37

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

Answer 37

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

Question 38

What is film fog and how do you reduce it

Answer 38

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