review 6 + 7 Flashcards
collimation
- Shaping the X-ray beam to radiating less of pt
X-ray beam is circular cross section
- no collimation large area affected – divergence
- Only need X ray photons to be hitting small rectangle – exact same size of receptor (approx. 4cm)
- Any around that is wasn’t – just unnecessarily irradiating the patient
collimation for lateral cephalograms
Only need to pass the front of facial bones and small section of cranial base
Need sella turcica in pit fossa
- Don’t want spine, posterior skull
Want to see angulation of teeth and jaws
- Traditional – triangular wedge shape instead of cone
- Top of area is the skull - no longer irradiating
- Bottom blocks neck and shoulders
- So only triangle wedge of TMJ, maxilla, mandible, pit fossa
soft tissue collimation in lateral cephalograms
Lead filtration collimating beam
- White line is border of collimation
- Could be done tighter – still larger area
Usually have another filtration – wavy to follow glabella, nose, chin
- Aluminium instead of lead (less strong)
- Some get through
- Show soft tissue outline in shade of white
Fewer x-ray in area – more attenuation so more likely to see soft tissue
- Reduce photon intensity in area
Want at source of X-ray to reduce radiation dose to pt
CBCT seen in
slices
or as a whole - reconstructed
pathology here
Ectopic canine – in midline
- Is it damaging the teeth crown is butting against
Get more info than from traditional panoramic
- Root will resorp
- Crown – enamel more resistant
pro of CBCT slices
don’t have superimposition worry
- as can see exactly whats there
e. g. sagittal slices, 1mm at a time
Crown of central incisor has root abruptly stopped by ectopic canine crown
- Significant external root resorption due to crown of canine
2nd to last see same has happened to lateral incisor
radiographs required for parallax
- 2 PAs norm
- But start with 1 and assess
- Endo – may need 2 as one root looks short and unable to id which one
parallax example
of extracting max 6
- 3 roots
- Mesiobuccal, distobuccal and large palatal
- Can see on 1 PA
- Assess if straight, curved
If one looks very curvy and unsure what one
- Get another PA – remove at certain angle
- Parallax to ID
- Especially if sectioning
X ray shadow concept
summary
Most attenuated – densest – bones – white
No attenuation – went through air – black
Gradient in between
X ray receptor convert different intensities of x ray photons into grey scale
viewing film radiographs
need light source (light box)
Ensure consistent level of light coming through
intra oral xray plates
3
2 digital
- Phosphor plate
- Solid state (wire)
1 film
- Film
solid state sensor Vs phosphor plate
more durable
solid state sensor
as Phosphot plate is a thin rectangle and phosphor crystal layer can be damaged
solid state sensor Vs phosphor plate
sensitive to visible light
phosphor plate
solid state sensor Vs phosphor plate
bulkier
solid state sensor
solid state sensor Vs phosphor plate
usually wired
solid state sensor
solid state sensor Vs phosphor plate
more expensive
solid state sensory
more components
but more durable so last longer
solid state sensor Vs phosphor plate
require additional scanning stage
phosphor plate
solid state sensor Vs phosphor plate
storage requires more physical space
phophor plate as need more physical ones
whereas solid state sensors single one can be used for whole mouth?
solid state sensor Vs phosphor plate
more comfortable for pt
phosphor plate as thinner, smaller and no wire
digital pros
- Storage less
- Easily shared
- No need for chemicals
- More efficient, less time consuming
- Can manipulate digitally
- Hard to lose – back up
film pros
- Higher resolution
- digital imaging size of pixels are determined by manufacturers ability to make pixels in receptor (SS) or scanner (PP)
- limited (but good enough for dentistry). Whereas film has crystals of black silver – tiny – higher resolution
- digital imaging size of pixels are determined by manufacturers ability to make pixels in receptor (SS) or scanner (PP)
- No need for diagnostic level computer monitor
- Not as bulky (SS) similar to PP
- Less likely to be misleading – cannot be manipulated
issues with film over digital
Many things can go wrong in film that can make poor image – unlike digital – consistent (hard to work out which caused issue – need to know before retaking)
true or false film radiography
over exposure = lighter image
FALSE
be dark
more xrays hitting receptor
true or false film radiography
developer solution too warm = dark image
TRUE
excited silver halide into black silver particles making darker
true or false film radiography
developer solution too concentrated = dark image
TRUE
true or false film radiography
developer solution too old = dark image
FALSE
less effective
not as many silver crystals converted into black silver
true or false film radiography
film left in developer solution too ling = dark image
TRUE
true or false film radiography
inadequate fixation = high contrast image
FALSE
white will be grey as inadequately washed away
true or false film radiography
film exposed to visible light before processing = light image
FALSE
foggy/clouding
fixation purpose
take black silver particles hardens into black area, unexcited undeveloped area
get rid – wash away
dark areas are darker and light areas are there as unexcited parts washed away
