Radiological Physics, Health and Safety
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What recommendations does each country interpret differently, with regards to radiation safety?
International Commission on Radiological Protection
Apart from radiographs, what other types of imaging modalities pose a risk to health and safety?
- Computed tomography
What is the absorbed dose of radiation measured in?
What is the quality factor of radiation measured in?
What happens to your body during acute radiation poisoning?
Body temperature goes up by 0.001°C. There is a period of well being. Then pyrexia, haemorrhage, diarrhoea, and hair loss. Cells that die are not replaced. 50% of people will die.
Give some examples of somatic effects of radiation
- Skin burns
What is meant by mutagenic effects of radiation
Damage to DNA, either to genes or chromosomes
Describe x-ray production
X-rays are produced at a cathode in a vacuum. It is a filament that gets heated and gives off electrons. These electrons sit around the filament until you apply a high potential difference between the anode and cathode. When these high speed electrons hit the target they give off x-ray photons in all directions, and a substantial amount of heat.
How do we get the potential energy required to generate x-ray photons?
To get the potential energy we take the voltage from the mains (230V) and boost it to 100+kV using a transformer.
What three things determine voltage?
- Number of turns
- Area of core
How else can we increase power whilst keeping the transformer small?
We can use frequency to increase the power
What is the photoelectric effect?
The photoelectric effect is when an x-ray hits the electron shell of an atom, pushes an electron up and causes light to be released when the electron falls back down
Describe the relationship between atomic number and the photoelectric effect
The higher the atomic number the greater the photoelectric effect
How do the following tissues appear on radiographs? a) air b) fat c) soft tissue d) bone e) lead
a) black b) dark grey c) soft grey d) white e) brilliant white
How do we control scatter?
- Distance - inverse square law i.e. the further away you are the less scatter you receive
- Using a grid - these are strips of lead with plastic in between. The photon that travels at an angle is blocked by a lead strip so only the photon travelling vertically down will reach the detector
- Have the kV as low as possible
What different types of grid can be used?
Stationary, parallel, focussed, potter-bucky
What is the disadvantage of using a grid?
- With stationary, parallel and focussed grids you can always see the lines of the grid on your radiograph which can be distracting
- Also when using a grid you have to increase the quantity (mAs) of X-rays produced and some machines may not be powerful enough to do this
What is collimation?
When lead shutters are used to try and minimise the area being exposed to x-rays
Why are intensifying screens often used when taking radiographs?
Intensifying screens have higher atomic numbers which when hit with x-rays give off light. The film used to capture the radiograph is more sensitive to light. This therefore decreases the exposure of x-rays and decreases the amount of scatter produced.
What is an advantage of digital x-rays?
Fewer repeats are done as the computer automatically makes the picture clearer (so fewer radiographs are thrown away)
Describe what is needed in a diagnostic imaging room
The room must be a controlled area with a set of local rules in place. There should be 1mm lead walls or equivalent for x-rays, 2mm for CT scans. The door should be locked when the room is in use and a warning light should be on to alert those outside.
Describe measures taken to protect personnel during diagnostic imaging
Personel should wear protective equipment such as gowns, gloves/sleeves, thyroid shields and glasses. The amount of radiation staff is exposed to should also be monitored using film badges or TLD.
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