Radiography Flashcards
what is a radiograph?
an image produced by xrays passing throuh an object and interacting with photogenic emulsion on a film
what is the job of a collimator?
restricts shape and size of formation
how is an xray produced?
electric current in filament passes through step down transformer
excitation of electrons gives off heat and outer electrons lost
= electron cloud
potential difference at cathode and anode
step up transformer
focusing cup points electrons to anode
attraction of positive and negative pulls electrons across
energy conversion = 99% heat and 1% xrays
copper absorbs heat and puts it into oil
xrays travel in all directions, some absorbed by lead - xrays pass through unleaded window
= beam of radiation
what are the types of xray spectra?
- continuous spectrum - brehstrahlung or breaking radiation, wide photon energy range
- characteristic spectrum - depends on anode material, emitted by loss of K and L shells
what are some xray properties?
travel in straight lines in free space form a divergent beam travel through a vacuum penetrate matter scatter absorb
uses of a peri apical?
detect apical inflammation assess perio problems trauma and fractures pre extraction position and presence of unerupted teeth endodontics implant evaluation
what is paralleling technique?
holder used to facilitate positioning
film parallel to tooth
accurate and reproducible image
what is bisected angle technique?
without a holder
operator dependent
not reproducible
what are the components of a holder?
bite block
indicator arm
aiming ring
how should the vertical plane of the film be positioned?
against the long axis of the tooth
what happens when the collimator down and pointing up?
elongation
what happens when the collimator is up and pointing down?
foreshortened
what affects the image size?
xray source to film distance
object to film distance
what does a long source to film distance cause?
what does a short source to film distance cause?
reduced magnification
increased magnification
where should the dot be placed in a periapical?
where should the dot be placed in a bitewing?
crown
palate
what should the distance of the controlled area be?
1.5 to 2m
what are the use of BW’s?
detect caries
monitor caries progression
asses perio status
asses existing restorations
what are features of horizontal bitewings?
what are features of vertical bitewings?
4 distal to 8 mesial crown and a third of roots 2 on each side pre molars and molars more of roots
why might horizontal overlap happen?
when is it acceptable?
what might it obstruct views of?
if tooth not parallel
crowding and tilting of teeth
ok if less than half the enamel is superimposed
miss early carious lesions
child of > 10 years use what holder size?
child under 10 years what holder size?
size 2
size 0/1
what does rectangular collimation reduce the dose by?
reduces dose by 50%
what is bisected angle used for?
changing position or shape of tooth
pt cant tolerate a holder
access is difficult
how is bisected angle technique done?
- place film as close to the tooth as possible
- observe angle of film to tooth
- operator bisects angle between tooth and film and angles x ray tube so beam is 90 to the bisector
- align collimator to the film
why might you use a bisected angle holder?
avoids irradiating finger
aids visualising angulation
reduces bending in film
stabilises film
what is an occlusal radiograph used for?
shows larger area than PA. Unerrupted teeth, cysts, SN’s.
what are types of film radiography?
what are types of digital radiography?
- direct and indirect action
- solid state sensor and PSP
what is direct film?
dental intraoral
xrays act on silver halide crystals in emulsion of film
what is indirect film?
extra oral
light from intensifying screens act on silver halide crystals in emulsion
what is DR?
solid state CCD or CMOS sensor
what is CR?
PSP
latent image produced by interaction of xrays and phosphor layer of plate
scanned by laser to produce an image
how does a PSP plate work?
phosphor layer traps xrays in electrons
plate in scanner and scanned by red laser = light released
light converted to electrical signal and image produced
bright light removes residual energy = re usable
how does solid state CCD work?
xrays hit sensor and light emitted
light hits photosensitive cells and image pixels produced
electrons released and electrical signal converted to image
what is the difference with CMOS compared to CCD?
photosensitive cells are isolated
what are advantages of digital imaging?
no chemicals easy to archive easy image transfer image manipulation dose limitation
what are disadvantages of digital imaging?
expensive
reduced isolation
back up
security
what is the job of the films outer plastic?
dry and protects film from light
what is the job of the films paper?
protects from light and supports
what is the job of the films lead foil?
absorbs xrays, prevents back scatter
what is the make up of radiographic film?
silver halide crystals - bromide and iodine in gelatin
how does direct film work?
photons hit silver halide crystals = sensitized = latent image
latent image produced by sensitizing silver halide crystals - not visibile
image made visible by reduction of silver bromide to black metallic silver
what is film speed?
sensitivity of film to xrays
dependent of crystal size
increased crystal size = faster film = reduced detail = reduced dose
how does indirect film work?
sensitive to light
light produced by phosphor crystals in direct proportion to xrays hitting the screen
reduced exposure needed for image = dose reduced = reduced detail image
what are the stages of film processing?
develop - latent image made visible wash - stop development fix - image made permanent wash - stop fixer dry - easier to handle
what is used as a developer?
develop for too long? too short?
developer too hot? too cold?
developer to strong? to weak?
phenidone, hyroquinone
dark light
dark light
dark light
what is the job of the fixer?
what happens to over fixed image?
under fixed?
change unexposed crystals to soluble to wash away
image removed if over fixed
green tinge
what types of processor exist?
automatic
manual
instant processing
what is the abosrbed dose?
amount of energy deposited into a medium
what s the equivalent dose?
accounts for the radio biological effectiveness of different radiations
what is the effective dose?
allows doses from different areas of the body to be compared
what are types of somatic effects?
deterministic
non deterministic
what are types of effects on the genetic offspring of those irradiated?
non determinsitic stochastic
what are deterministic effects of radiation and when do they occur?do they occur in dentistry?
will occur above a threshold
hair loss skin erythema cataract GI upset erythropoiesis suppressed
does not occur in dentistry
what are non determinsitic effects of radiation?
random development do no occur at any threshold
increased probability with increased dose
leaukaemias and solid tumours
occurs in dentistry
what is the intra oral cancer risk?
what is the DPT cancer risk?
- 06-0.7 in 1000000
0. 29-1.9 in 100000
how is dose contained?
justification - exposure must be justified
optimisation - ALARP
dose limitation
when is lead protection used in dental radiography?
thyroid in the main beam
when can caries be radiographically detected?
30-40% demineralisation has to have occured
what can be mistaken for caries?
cervical burnout
shadows
radiolucent restorations
what are xrays used for in perio disease?
to show the remaining bone in relation to the root
why is there more scatter min skull radiography?
increased field of beam
what is an antiscatter grid?
stop photons scattered in pt reaching the film
lead and plastic
what are PA of the mandibles used for?
fractures
cysts and malignancies
what are reverse townes used for?
trauma and pathology
head and neck of condyles
what lateral obliques of the jaw used for?
dental assessment in special needs pts and kids. Assess wisdom teeth. Fractures. Pathology.
what are ceph radiographs used for?
ortho assessment. Pre orthagnathic surgery
what are Occipito mental radiographs used for?
facial bone fractures
what legislations are in place for dental radiography?
ionising radiations regulations 1999
ionising radiation medical exposure reg 2000
what is the job of IRR 99?
protects public and those working with radiation. Equipment
what is the job of IRMER 2000?
protects those being irradiated
for general loss of attachment of 4-5mm take what type of bw’s?
for loa of >6mm?
horizontal bws
vertical bws
what problems does a DPT present?
anterior region - spine superimposition
overlap at premoalr region/molar region can obscure bone
lack of fine detail and burnout
what topics undergo quality assurance?
image quality xray equipment processing working procedures training audit
what percent of graded films should be 1,2,3?
1 >70% of films
2< 20 % of films
3<10% fims
what does initial acute inflammation look like on an xray?
nil or widening of the PDL
what does initial inflammation spread look like on an xray?
loss of lamina dura at the apex
which can lead to periapical bone loss
what does initial chronic inflammation look like?
dense sclerotic bone
