Radiographic positioning

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Radiographic positioning
2014-12-02 06:59:55

Vet Med - Module 7 - Week 1
Show Answers:

  1. What is the quality of a radiograph determined by?
  2. What does mAs equal?
    mAs = current x how long the X-ray machine is functioning for
  3. Many low power machines have a restricted range of mAs.  How do you compensate for this?
    You take the kV you've calculated and add 10
  4. Why is measuring the thickness of an animal to get our exposure factors not always accurate?
    If we simply measure the animal we are not taking into account bone, soft tissue, air and fat, which all have different effects on exposure factors.
  5. What factor must be taken into consideration when setting up radiographs in equine practice compared to small animal practice?
    Distance - the machine in small animal practice is usually fixed but in equine practice it has to be moved around the animal so it is important to keep the distance constant and make sure the plate is perpendicular to the tube
  6. What can be the cause of a radiograph being a) underexposed b) overexposed?
    • a) kV too low / mAs too low
    • b) kV too high ('toast')
  7. What is penumbra?
    Unsharpness or blurring at the edges of a radiograph
  8. How do the following help reduce penumbra? a) object to film distance b) focus to film distance
    • a) If you move the object closer to the plate this reduces the amount of penumbra i.e. keep the organ as close to the plate as possible
    • b) If you increase the distance from the tube to the patient you reduce penumbra
  9. What is the standard focus to film distance in small animal practice?
    100cm (but if the X-ray machine is not powerful this can be reduced to 75cm)
  10. What else can cause blurring of the radiograph?
    Movement unsharpness - often seen in radiographs of the chest and heart as there is constant movement during them being taken
  11. Give examples of some positioning aids used during diagnostic imaging
    • Halters
    • Ropes
    • Sandbags
    • Troughs
    • Cassette stand
  12. Why are oblique views used when taking radiographs?
    Used in very thick tissue or areas when you get poor penetration.  They are also used to skyline structures and project tissue out of the way.
  13. What are some issues with equine radiography?
    • The x-ray beam is horizontal (health and safety risk)
    • GA: risks
    • Sedation: care must be taken
    • Oblique views are mandatory to get full information
    • Horses have thick joints so distance and centring must be on point
  14. What aspect of the joint will a DLPMO view skyline?
    Medial aspect of the joint
  15. What aspect of the joint will a DMPLO view skyline?
    Lateral aspect of the joint
  16. What are some major faults when taking radiographs?
    • Poor exposure factors
    • Superimposition
    • Rotation
    • Not centred
    • Movement blur
    • "Criminality" - manual restraint of patients (which is illegal in the UK without strong clinical justification)