Intro to Radiology Flashcards
(43 cards)
Radiographs have similar properties to … but …
- shadows made by light
- the rays also pass through object to varying degrees
Principles of shadow casting
- radiation source small as possible
- source-object distance large
- object-film distance small
- object and film parallel
- x-ray beam perpendicular to object/film
Define ‘resolution/sharpness’
measures how well the details (boundaries/edges) of an object are reproduced
What does a line pair gauge do?
measures sharpness/resolution
4 types of un-sharpness
- movement
- geometric
- photographic (if using film)
- pixel size
What is geometric unsharpness?
- zone of unsharpness along the edge of images in a radiograph
How are magnification and resolution linked?
- source to object distance (the greater, the less divergence of the beam, so less magnification)
- object to film distance (the greater, the more magnification)
Decreasing the focal spot size increases …
sharpness
Increasing the traget-teeth distance increases what?
sharpness
2 things that increase sharpness
- decrease focal spot size
- increase target-teeth distance
Explain photographic unsharpness
- E-speed is normal
- F-speed show larger crystals and more unsharp image
You may see … due to angulation
distortion
How should intra-oral radiography be done for ideal images?
- image recorder absolutely flat
- film parallel to long axis of object (tooth)
- recorder as close as possible
- central of x-ray beam should be perpendicular to both object and film
- distance between x-ray source and object should be large with small object film distance
If the placement of the radiograph is wrong, correction?
- place receptor according to placement guidelines
- to cover all structures
If the foreshortening of the radiograph is wrong, correction?
decrease vertical angulation of x-ray beam
If the elongation of the radiograph is wrong, correction?
increase vertical angulation of PID
If the overlappingof the radiograph is wrong, correction?
direct x-rays between contacts of the teeth
If the cone-cutting of the radiograph is wrong, correction?
center x-ray beam over the image receptor
If the underexposure of the radiograph is wrong, correction?
increase exposure factors - check for large patient size
What’s the paralleling technique?
- film palced in holder and positioned parallel to long axis of the tooth
- x-ray beam is aimed at right angles to tooth and film
- by using a holder the technique is reproducible
Explain the bisected angle technique
- film placed as close to the tooth as possible without bending
- angle between long axis of tooth and film is assessed and bisected
- beam is aimed at right angles to this bisected line
Advantages of the paralleling and bisected techniques
- sharper, less distorted images
- correct centring of image on film
- easier to do - less guesswork
- reproducible
Disadvantages of paralleling and bisected angle technique
- difficult or impossible if palate low or floor of mouth shallow
- can be difficult is using rubber dam clips as in endodontics
How to make imaging reproducible?
- film holder with putty matrix attached is the same everytime
- dismantle from holder and leave putty with bite block for further imaging (same beam angulation next time)
