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