Image receptor and processing Flashcards
types of image receptors and processing
- film –> chemical processing –> hard copy (non digital)
- psp plate –> scanner –> computer display (direct-indirect(
- ccd/cmos –> computer display (direct-direct)
components of x ray film (analog - use intraorally)
and function
x ray tube –> tooth –> outer covering of film pack (waterproof) –> inside film pack: black paper –> film w raised dot facing x ray tube –> black paper –> lead foil –> outer covering of film pack (waterproof)
- black paper: prevents light penetration
- film
- raised dot provides orientation
- in one single emulsion film has
–> over coat: provides protection
–> emulsion: active layer (silver halide crystals)
–> base: physical support - outer covering: waterproof
- lead foil
- prevent scatter that leads to radiation fog
- reduce pt exposure by absorption of residual radiation
component of screen film (analog -extraoral)
x ray tube –> tooth –> cassette front –> intensifying screen (phosphur) –> double coated film –> intensifying screen (phosphur) –> cassette back
- intensifying screen has active phosphur layer –> amplify x ray beam + emit light when exposed to x ray beam –> reduce patient dose
difference between film and screen film
screen film has intensifying screen but film dont have
formation of latent image and processing of film/screen film - steps for film but can apply for screen film
- in film, silver halide (mostly AgBr) is suspended in gelatin matrix
- x ray beam can ionise AgBr into Ag+ and electrons
- sensitivity specks trap electrons and Ag+ –> form latent image
- work in dark room
- put in developer (hydroquinone and phenidone) –> reduces Ag+ to black metallic silver grains –> means exposed crystals will appear as black metallic silver grains
- put in water
- put in fixer (ammonium thiosulfate) –> removes unexposed and undeveloped crystals –> left with exposed crystals that are black metallic silver grains –> forms image
- put in water
- view physical film in light box
component of PSP (digital)
- used for intra and extraoral
1. plastic barrier envelope
–> hygiene purpose
–> protect from damage
–> protect active site from light
2. plate
–> protective layer
–> phosphur layer (has barium fluorohalide with europium, active side)
–> support layer
formation of latent image and processing of psp (indirect)
- in phosphur layer –> barium with fluorohalide europium –> has valence and conduction band
- x ray photon cause e- (eu2+) in valence band to gain energy and move up to conduction band. Amount of e- that move up proportional to x ray exposure
- e- (eu3+) trapped in f centre of conduction band –> forms latent image
- laser in scanner cause e- to return to valence band (become eu2+) and emits light –> this means that the plate is erased and ready to be used again
- light is collected by fibreoptics and converted by photomultiplier tube to electrical voltage
- ADC (analog to digital converter) will quantify and sample the voltage signal at each pixel
- computer display will display image based on pixel’s location and shade of grey assigned to each pixel.
what if PSP plate face wrong direction
- means not black in side
- latent image is formed from inactive side (black)
- scanner scans from active side (blue)
- hence image will be displayed as horizontally flipped –> eg. if taking #35-38, image appears to be #45-48
what if psp plate blue side exposed to light after latent image formation?
- light exposure mimics laser from scanner
- e- returns from conduction band to valence band and emits light that is not captured by fiberoptics and photomultiplier tube
- when psp plate scanned by scanner and laser is emitted, less light emitted –> lighter image
component of ccd/cmos (digital) - both intra and extra oral
intraoral
- x ray –> tooth –> front housing -> scintillator layer –> fiberoptics face plate –> imaging chip –> electronics substrate –> back housing and cable
extraoral
- linear array
- used in dpt
processing of ccd/cmos (direct)
in each pixel
- scintillator converts x ray photon to light
- light cause electrons in valence band to gain energy and move up to conduction band –> this forms “electron hole pair”
- more electron hole pair, when more exposure
- electron detected by electronic readout –> voltage is transmitted to ADC (analog to digital converter) that’s connected to computer
advantage of digital imaging compared to analogue (8)
- quicker
- lesser radiation
- easy to use and easy image processing
- chemical free
- can enhance image
- easy retrieval/storage
- easy communication
- can integrate into electronic chart
disadvantage of digital imaging (4)
- high cost in –> initial set up + convert previous records to digital system + replacement parts
- learning barrier
image characteristic terms
- density/ brightness
- contrast –> increase density = decrease contrast (more grey)
- spatial resolution: decreased resolution - blur
- noise: grainy/noisy
- cause:
—> inadequate exposure
—> poor scatter control –> decreased contrast
—> artefacts/film fog
