Imaging Flashcards
What are x-rays?
electromagnetic radiation used to create an image
What is a radiograph?
the image on a display screen - a shadow picture and 2D projection
Properties of x-rays
- high energy and short wavelength
- ability to penetrate materials and cause changes at atomic level
- can lead to ionisation
- no charge/mass
- invisible
- travel in straight lines
What is ALARP?
radiation safety = As Low As Reasonably Practicable
- dose
- personnel
- times
- distance
- shielding
Properties of x-ray beam
Quality = penetrating power of the beam
Intensity = amount of radiation in the beam
What is the effect of changing kV?
- increasing kV
= increased electron acceleration, increased energy of electrons, increased no. of x-rays
therefore x rays = increased penetrating power therefore decreased contrast
What is the effect of changing mA?
mA controls the current applied to filament
- increasing mA = increased tube current, increased no of electrons = more x rays produced
HOWEVER
energy of x-rays unchanged
Effect of kV
quality and intensity
Effect of mA
intensity only
Computed radiography (CR)
- phosphor plate held in cassette
- electrons energised to form latent image (trapped energy)
- cassette placed into reader and plate removed
- plate scanned by laser and trapped energy released as visible light
- light detected by photomultiplier and converted into electronic signal
- signal processed by computer and image produced
Direct radiography (DR)
- x-rays stimulate sensor panel that sends electronic signals direct to computer
- sensor panel can be separate or mounted on table
What does Pink Camels Collect Extra Large Apples stand for?
Positioning Centring Collimation Exposure Labelling Artefacts
Why is collimation important?
reduces production of scattered radiation - reducing hazard and appropriate processing of the image
What is an optimal radiograph?
needs to show wide range of differentiated shades of grey
How to limit scattered radiation?
- good collimation
- low kv
- use of radiographic grid if necessary
How do you describe abnormality on a radiograph?
- number
- location
- size
- shape
- margination
- radiopacity
- internal architecture
- function
What should a good radiograph look like?
- accurate portrayal
- easy perception
- sharp shadows
- range of shades of grey
- no misleading artefacts
- consistent results
- no unnecessary risks
What is different about taking radiographs on a horse?
need 4 standard views as the equine limb is too thick
What preparation needs to be done before imaging?
try to starve cats and dogs 24 hours before abdominal radiography and allow to urinate and defaecate beforehand
Assessing axial rotation in lateral thoracic view
caudodorsal rib heads should be superimposed and joined at the top
