Radiographic safety Flashcards
X-rays are a form of what type of radiation?
Electromagnetic
On the electromagnetic spectrum what type of wavelength and frequency do x-rays have?
Short wavelength and high frequency
- inversely proportional to each other
What makes x-rays damaging to tissues?
High energy - able to produce ionisation
X-ray photons are produced when high speed electrons hit what metal target? Describe how this happens.
Anode
- the electrons are produced at the cathode and are accelerated by potential difference
Why is the process of x-ray production inefficient?
Lots of energy is released as heat
What controls the size and shape of the primary beam?
Lead collimators
What are the 3 tube variables that the radiographer can alter?
- kilovolt peak (kVp) - potential difference between anode and cathode
- milliamps (mA) - number of electrons accelerated
- seconds - length of exposure
What is the anode made from?
A bevelled rotating disc of tungsten
What is penumbra? how can it be reduced?
Blurring at the edge of structures
- reduced by having a smaller effective focal spot
How can the size of a focal spot be decreased?
Decreasing width of electron beam that is hitting the anode
Decreasing the angle of the anode
What is the purpose of placing an aluminium filter in the path of the primary beam?
Removes low-energy x-ray photons which are of no use
What is used to control the size of area irradiated by the primary beam?
Collimators
Which 2 factors does photoelectric absorption depend on?
- Effective atomic number
- Number of atoms per unit volume (density of tissues)
What is scatter and what does it cause?
When photons continue in different directions with lower energy and are not absorbed.
Results in random film/image blackening in the surroundings
Photoelectric absorption has predominant interaction with…?
- Low energy photons
- High atomic number tissues
Scatter has predominant interaction with…?
- Medium-high energy photons
- Low atomic number tissues
What does kV control? What happens when you increase it?
- The energy of x-ray photons in the primary beam
- More photons have sufficient energy to penetrate the patient
What do mAs control?
The number of x-ray photons produced
What is exposure a combination of?
mAs and kVs - they are exposure factors
To double exposure how much do mAs and kVs need to be increased by?
Increase mAs by 100%
Increase kVs by 15%
On a radiograpah an area with complete exposure will appear…?
Black
What are the 5 basic radiographic opacities from black to white?
Air Fat Soft tissue/fluid Mineral (bone) Metallic
Is a light film over or under exposed?
Under
What is meant by dynamic range in radiography?
Range of x-ray exposures over which a useful image can be obtained
Describe the relationship between exposure, signal and dynamic range in:
- conventional film
- digital systems
- narrow dynamic range, non-linear relationship between exposure and signal (s-shape on graph)
- wide dynamic range, linear relationship between signal and exposure (straight line)
What is the main health concern when it comes to radiography?
Ionising radiation
Which other scanning method uses ionising radiation?
CT scanning
What causes ionising radiation?
Scatter - travels in all directions
What are some deterministic effects of ionising radiation?
Tissue reactions related to cell death e.g. skin burns, cataracts, bone marrow suppression, sterility
What are the stochastic effects of ionising radiation?
Cell mutation related to DNA damage e.g. cancer inductions, birth defects
What unit is the effective radiation dose given in?
sievert (Sv)
Why is radiation weighting used?
Not all radiation is given in equal doses
It accounts for the biological effect of radiation type on tissue type
What is the calculation for the absorbed radiation dose?
Energy imparted into the tissue/Mass of the tissue
Who governs all work with ionising radiation?
Ionising radiations regulations 1999
Safe working with radiation requires cooperation of which 3 groups of people?
- Health and safety executive
- Radiation Protection advisor
- Employer
What are the 3 basic principles of radiation protection?
- Ionising radiation should only be used where there is a clear justification for the procedure
- Any exposure to personnel should be kept as low as reasonably practicable
- No dose limit to personnel should be exceeded
Doses over what level must be investigated?
15mSv per year
The radiography room must be large enough for..?
- All involved to be at least 2m away from the primary beam
- Behind a protective screen/barrier
What are boundary shielding requirements for scattered radiation and the primary beam?
- 0.5mm lead for scattered
- 2mm of lead for primary beam
