Intro to Radiology Flashcards
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)
Uses of bitewings
- caries in posterior teeth
- deficient/leaky restorations
- poor contoured restorations
- calculus
- early periodontal bone loss
Role of bitewing holders
- improve centring
- reduces overlapped teeth
- serial radiographs comparable
Bitewing technique
- beam is aimed at right angles to the film and through the interproximal space
- to prevent overlap
Vertical bite wing uses
- useful for demonstrating mild to moderate alveolar bone loss
- if probe depth is less than 6mm
Features seen in occlusal radiography
- maxillary projections
- mandibular projections
Types of maxillary projections
- upper standard occlusal
- upper oblique occlusal
- vertex occlusal
Types of mandibular projections
- lower 90 degree view (true)
- low 45 degree view (standard)
- lower oblique occlusal
Uses of upper standard maxillary occlusal radiographs
- periapical assessment of upper anterior teeth
- presence of unerupted canines, supernumeries
- for parallax in conjunction with DPR
- size of cysts/tumours
- assessment of alveolar fractures
What can upper oblique maxillary occlusal show that standard occlusal can’t?
- shows premolar and molar areas
Uses of vertex occlusal radiographs
Problem
- similar to standard view
- but gives plan view of palate - will show buccal/lingual position of unerupted canines
- not recommended due to beam passing through patient
Uses of lower 90 degree mandibular occlusal radiographs
- detection of submandibular calculi
- assessment of bucco-lingual position of mandibular teeth
- evaluation of bucco-lingual cortical expansion
- assessment of mandibular fractures
What do lower 45 degree mandibular occlusal radiographs show that true lowers don’t?
- periapical view of lower anterior teeth
Use 60KVp on radiograph when …
looking for foreign bodies in soft tissues
The lower the KVp the increased …
contrast
What is a dental panoramic radiograph?
- called a tomograph - a slice through the jaws for example
- gives excellent overview of anatomy of maxilla and mandible
Other names for dental panoramic tomogram/DPT
- OPG (orthopantomograph)
- panoramic
Uses of dental panoramic tomographs
- evaluations of periodontal/orthodontic status
- trauma
- caries assessment (but not ideal)
- assessment of third molar position related to ID canals
- assessment for tumours in jaws
- TMJ outline (not ideal)
What can you do to reduce radiation in radiographs?
- not picture and remove centre sextants
When would you do a lateral cephalogram?
orthodontic assessment
