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What will protective equipment including a lead gown, lead sleeve and thyroid shield protect against? a) The primary x-ray beam (within the collimated area) b) scattered radiation c) A and B d) Neither A nor B
b) Scattered radiation
Why is it important to store protective clothing properly (put gowns on hangers, etc)?
To stop them becoming creased or damaged which will lead to cracks in the lead rubber and render the clothing ineffective as radio-protection
What equivalent thickness of lead (in mm) should be present in: a) protective gowns/aprons b) gloves/sleeves?
When in the UK is it appropriate to restrain a small animal manually for radiography? Give an example when this might be appropriate
Manual restraint may only be used when there is essential clinical justification e.g. in cases of severe dyspnoea
What is the function of an intensifying screen and how they do improve radiation safety?
The intensifying screens emit light when excited by x-ray photons. Film is more sensitive to light. Therefore, the use of intensifying screens results in a considerable lower radiation dose to the patient and causes less scatter to be formed, as it allows a dramatic reduction in the necessary exposure factors.
Why is it important to limit the scattered radiation reaching the cassette?
As scatter results in non-specific grating of the cassette which can ruin the quality of the radiograph
Over what tissue thickness should a grid be used?
What is one of the major problems when using a grid?
The use of a grid will require an increase in mAs (usually x2 or x4) as a significant number of the x-rays will be absorbed by the grid. This will increase the power demand on the x-ray tube, as well as increasing the scatter sent out into the room, potentially increasing the risk to personnel involved in the radiographic procedure.
What aspect of the primary x-ray beam does kVp control? What is the effect of increasing kVp on the resulting image in terms of blackening and contrast?
kVp determines the energy the x-ray photons have when they leave the x-ray tube. The greater the energy the greater thickness of tissue x-ray photons can pass through. Therefore, increasing kVp will increase the number of x-rays reaching the cassette, increasing the image blackening and decreasing image contrast.
What aspect of the primary x-ray beam does mAs control? What is the effect of increasing mAs on the resulting image in terms of blackening and contrast?
The quantity of x-ray photons produced. Increasing the mAs will therefore increase the number of x-rays produced and will increase the number of x-rays reaching the cassette in areas where the x-rays have sufficient energy to penetrate the patient - this will result in increased image blackening in these areas, but not in areas where the x-rays do not have enough energy to penetrate the patient, and so this will result in an increase in image contrast (as long as kVp is not altered)
What is the function of callipers? Why will simple measurement of the animal not always produce a good image - what is the other factor that might vary the exposure settings?
- Callipers are used to measure the thickness of an animal and therefore used for selection of appropriate exposure factors
- Simply measuring the animal does not take into account the type of tissue the x-rays are penetrating. Fat, gas, fluid and soft tissue all have different effects on x-rays and will vary the exposure settings.
What is the formula used to calculate adjustments of mAs?
New mAs = Old mAs x New Film-Focal Distance / Old Film-Focal Distance
What is the down side of reducing the film-focal distance?
It can increase the amount of penumbra seen on the radiograph
What ideally defines the controlled area of a small animal radiographic set-up?
The controlled area should be defined by physical boundaries such as walls
What indicators should be present at the entrance to the x-ray room?
A red warning light which should be wired so as to illuminate automatically when the x-rays are being generated. Also a warning sign incorporating the trefoil radiation symbol and a notice e.g. 'X-ray controlled area - do not enter when light is on'
What is the minimum distance unprotected personnel should be from the primary x-ray beam?
What additional safety concerns does equine radiography produce when compared to small animal radiography?
- Horses are usually radiographed while conscious and standing. X-ray equipment and personnel may be vulnerable if the patient becomes uncontrolled.
- Horizontal projections are frequently necessary, presenting safety issues in terms of distance and direction of the x-ray beam
- Ofter higher exposure factors due to patient size.
How can equine field radiography be made as safe as possible?
- Ensure anyone that does not need to be present is kept away from the area
- All persons involved should wear protective equipment
- Wooden blocks can be used to position equine feet
- If possible stand 2m away from the primary beam
- Make sure there is a suitable stopper at the other side of the primary beam e.g. thick concrete wall or lead plate
- Use confined area if possible
- Minimum number of personnel