SUMMARY Flashcards
name the types of intra-oral x-rays
periapicals
bitewings
occlusal - max and man
name the types of extra-oral x-rays
DPT
Lateral cephalogram
Postero anterior mandible
Lateral oblique mandible
occipito-mental views of facial bones
what creates the difference in detail between intra and extra oral radiographs?
the distance between object and receptor
what is the atomic mass number?
number of protons + number of neutrons
what is an isotope?
same number of proton
different number of neutrons
what is the most favourable intra oral technique and how is it performed?
paralleling
uses holder which is parallel to teeth
what intra oral technique involves patient holding film?
bisected angle
what are the 4 types of holders and what are they used for?
red - bitewings
blue - anterior
yellow - posterior
green - endo
what are the different sizes of phosphor plates?
0 - periapical and bitewings
1- periapical (adult), all areas (children)
2 - posterior (adult)
4 - occlusal
in intra-oral radiography, what is the ideal vertical plane?
parallel to long axis of tooth
IF NOT
elongation of teeth
in intra-oral radiography, what is the ideal horizontal plane?
parallel to dental arch
IF NOT
overlapping teeth
in intra-oral radiography, what is the ideal position of the beam?
right angle to tooth and receptor
what would be the outcome if the beam was angled down, up, or poor horizontal angulation?
down - elongation
up - foreshortening
hor. - overlapping
what is at the end of the x-ray tube that helps reduce exposure?
collimator
where should the dot on the receptor be placed for periapical, and bitewings?
periapical - crown of tooth
bitewing - palate
what are the ideal magnification distance types?
x-ray source -> receptor - LONG
object -> receptor - SHORT
what is the difference in dose between vertical and horizontal bitewings?
vertical double exposure dose
what would you do if patient cant tolerate the plastic of the holder?
paper tab stuck to receptor
explain the difference between direct and indirect film and what they are used for?
direct film - intra oral
x-rays directly act on silver halide crystals in emulsion.
indirect film - extra oral
light from intensifying screens act on silver halide crystals in emulsion.
what are the types of digital receptors?
PSP - phosphor plate
CCD/ CMOS - solid state
what creates the latent image with PSP?
x-ray energy stored in the electrons of the phosphor crystals
how is an image created with the phosphor plate?
phosphor layer scanned by red laser
stored energy is released as blue light
blue light is collected by scanner and converted to image
what is the phosphor coating of PSP?
Barium fluoride
what does an ACD do?
converts light to digital signal
each pixel is assigned a numerical value according to intensity of light
pixel values represent shades of grey
how is an image on PSP erased?
exposed to bright light
what are the layers of CCD?
Front cover
Scintillator layer
Silicon wafer
Back cover
how does CCD work?
- x-rays hit off sensory in the scintillator layer
- this gives off light and hits the silicon wafer cells which make up pixels of image
- electrons in each pixel are released and converted to a electrical signal (voltage)
- computer converts into image
what differs CMOS to CCD?
CMOS - singular pixels (electrically isolated)
CCD - lines of pixels
what is the system for storing images?
picture archiving and communication system
what are the contents of a film packet?
barrier wrapped film
outer plastic wrapping
black paper
lead foil
what are the layers of a film?
base - plastic
blue anti-glare tint
adhesive layer
double emulsion
gelatine layer
what does the film emulsion consist of?
silver halide crystals suspended in gelatin
what is the function of gelatin in a film emulsion?
even distribution of crystals for readily absorption of liquid
explain direct action image formation
- x-ray beam hits silver halide crystals in emulsion
- silver halide becomes sensitised
- latent image production
what is the main reaction in direct action image formation?
silver bromide crystals reduced to black metabolic silver
relate film speed to crystal size and detail
larger crystal - faster speed - less x-rays - less detail
what does an intensifying screen consist of?
base - polyester
phosphor layer
supercoat
explain indirect image formation?
- x-ray photons hit phosphor crystals in intensifying screen and give off light
- light hits silver halide crystals in emulsion
- silver halide crystals sensitised
- latent image production
what may pressure do to a film?
sensitise silver halide crystals
what are the stages of film handling?
develop
wash
fix
wash
dry
What does developing do?
makes latent image visible
- sensitised silver halide crystals are acted on by developing agent (phenidone) and hydroquinone
what reaction is involved in developing?
silver bromide reduced to silver and bromide
what does a developing solution contain?
developing agents - phenidone and hydroquinone
activator - calcium carbonate
restrainer - potassium bromide
preservative - sodium sulphite
solvent - water
what does fixing do?
makes image permanent
unexposed silver halide crystals are made soluble and washed away
what does fixing solution contain?
clearing agent - ammonium thiosulphate
acidifier - acetic acid
hardener - aluminium chloride
preservative - sodium sulphite
solvent water
what does washing do?
stops development by removing unexposed silver halide crystals
what happens if an image is under washed?
tacky
silver/green
deterioration
what are deterministic effects of radiation?
non-stochastic biological effects of radiation that WILL occur
a. acute
b. chronic
what are non-deterministic effects of radiation?
stochastic biological effects of radiation that MAY occur
what is the mean dose for dental workers?
less than o.1mSv
how far away should you stand from machines?
2m
what is IRR17?
equipment and protection of staff and public
what is IR(ME)R17?
protection of patients
what is an RPA?
Radiation protection advisor
- ensures organisation has adequate radiation shielding to protect staff, operators, and patients in the radiation area.
what is an RPS?
Radiation protection supervisor
- securing compliance with IRR17 in respect of work carried out in an area subject to local rules.
what is an MPE?
performs radiation dose/ risk assessment for all radiation exposures.
what is the role of the employer?
- produce written procedures
- produce protocol for taking radiographs
- appoint an RPA/MPE and RPS
- ensure staff read local rules
what is the role of the refferer?
refer individuals for exposure
what is the role of the dental nurse?
without qualification - process radiographs
with qualification - take radiographs “on prescription” of another dental registrant
what is the role of the dental hygeinist?
prescribe, take, process, and interpret
what is the role of the dental technician?
take and process ONLY on radiographs relating to providing removable dental appliances
what happens if dose is greater than intended?
inform patient
duty of candour legislation
inform referrer
what does the quality assurance programme asess?
- image quality
- x-ray equipment
- processing (film and digital)
- working procedures
- training
- audit
how is image quality rated and what are the desired percentage rates?
1 - excellent (more than 70%)
2 - diagnostically acceptable (more than 20%)
3 - unacceptable (more than 10%)
what happens to rate 3 films?
reject film analysis
- eliminate at end of each month anf categorise faults
how is equipment checked for patient doses?
dosemeter for radiation output
what information does the box of films contain?
film size
number of films
liability notice
best before date
storage instructions
how is the developer checked?
sensitometry
- daily
- compare with fresh film
step wedge test
- different thicknesses of metal
- shows steps of blackening when radiographed
readily exposed test film
- unwrap in darkroom conditions
green - good
amber - OK
red - exhausted
what does an exhausted developer do to an image?
pale
what are the causes of fogged film?
- light entering daylight loading system/ darkroom
- incorrect safelight filters
how do you check for fogging?
coin test
- coin placed on intra oral film for 5 mins
- once removed, radiograph and check for fogging
how are large digital sensors and EO cassettes checked?
test tool
number of coloured squares - contrast and brightness
number of boxes displaying line pairs - resolution
what are the extra-oral views?
postero-anterior mandible
lateral oblique mandible
DPT
lateral cephalogram
occipito mental views
sialography
what are the 3 positioning landmarks?
radiographic baseline - outer canthus of eye to EAM
frankfort plane - inferior orbital border to EAM
maxillary occlusal plane - ala of nose to tragus of ear
what is is called when x-rays pass through tissue and some scatter?
compton scattering
what is an anti-scatter grid?
narrow strips of lead alternating with plastic - absorbs photons
what is the setup for postero-anterior mandible?
- patient faces film with nose and forehead touching
- RB 90dgeree horizontal to film
what are the 3 positions for a lateral oblique mandible view?
isocentric
vertical angulation
horizontal angulation
how is patient set up into isocentric position for LO mandible?
- supine
- machine horizontal plane
- top of head tilt towards film
how is patient set up into vertical angulation position for LO mandible?
- patient hold cassette parallel to area
- tube head beneath lower border of mandible that isnt being examined
- angles slightly upwards
how is patient set up into horizontal angulation position for LO mandible?
- patient hold cassette parallel to area
- tube head positioned along occlusal plane, just below ear
what machine takes a later cephalogram?
cephalogram
what is the positioning for a lateral cephalogram?
- mid-sagittal plane parallel to film
- ear rods
- x-ray aimed at EAM
what makes soft tissues visible in a lateral cephalogram?
aluminium filter
what are the 3 occipto mental views?
OM 0
OM 10
OM 30
what is a tomogram?
slice/ section of tissue in focus
explain how objects are seen in a dental panoramic depending on their location with focal trough?
further away from focal trough - blurred
within focal trough - sharp
explain beam movement with narrow beam tomography, and its focal trough
synchronised movement of tube head and film
focal trough arched shaped
what is the issue with arch shaped focal trough?
ectopic teeth may not be seen
how does a CT scan work?
- x-rays pass through body
- attenuation of beam measured by detectors
- computer assesses radio-opacity of each voxel
- Hounsfield number for every tissue
what is the Hounsfield scale?
air = -1000HU
water = 0HU
cortical bone = 1000HU
what is the kV of CT tube?
120kV
what is a voxel?
volume of tissue
what makes CBCT differ from CT?
- lower dose
- higher FOV
- shorter exposure
what produces MRI?
radio waves
what produces SPECT?
gamma rays
what produces PET?
positrons
when would the focal trough need to be smaller?
children
abnormal shaped patients
better visualisation of specific anatomical areas
what is an orthogonal view?
90 degree to teeth
where is the x-ray source in relation to the focal trough?
lingual
explain vertical angulation?
structures further away from receptor will be projected further up on the image
what angle is the beam normally in panoramic?
slightly upwards by 8 degrees
