CR and DR systems Flashcards
what does CR and DR stand for
computed radiography
digital radiography
what are the components of a conventional film/cassette
cassette front
intensifying screens (scintillated layer)
radiographic film
lead foil
cassette back
what is the intensifying screen of a film made of
(phosphors)
green glow: gadolinium oxysulphate
blue glow: caesium iodide
why is a XR film dual sided with screens
increased detectability so reduced dose
why is a darkroom lit up red
because the films contain phosphor which is green or blu sensitive
what do you use to retain a latent image in XR film
silver halides
how is the image produced from a XR film
retained image using silver halides
then silver is removed from image via chemical processing leaving a hardened film
what are the 5 components of a CR system
- mechanical drive
- laser scanner and mirror
- light channelling guide
- light collection
- white light
describe the function of all 5 components of CR system
- mechanical drive takes in cassette opens removes and replaces plate, closes then returns to slot
- laser scanner and mirror usies helium-neon and excited the plate with red beam to cause it to emit blue light
- light guider guides it
- light collection uses photomultiplier tube or charged couple device to change from analog to digital
- white light is used to erase plate
exactly how are latent images read
laser energy excites electrons releasing them from traps in conduction back back down into the valance band with excess energy emitted as light
light picked up by photomultiplier tube, converted to digital signal, building up line by line to create digital image
why does a DR detector need a docking stand
to download images if made remotely and recharge battery
why does a DR detector need internal support
provides structure of image matrix (usually glass)
what is the use of an antenna in a DR wireless detector
data sent by wifi to computer for image to be viewed
where is the processed image from a dr detector sent to?
PACS
picture archive communication system
what are the 2 ways xrays are converted into electrons in DR
direct DR: amorphous silicon or selenium converts energy directly into electrons
indirect DR: XR converted into light by scintillator then into electrons
what are the 2 materials that convert energy into electrons in direct DR
selenium or amorphous cilicon
explain the process of indirect DR
- xrays converted to light with thallium-activates caesium iodide scintillator needed CsI:Th
- light converted to electrons by thin-film transistor
- electrons converted to digital signal by matrix of hydrogenated amphorae silicone a-Si:H
- signal passes along integrated electronic circuits
- data transmitted by electronic amplifier circuits around edge of panel
what can happen if you drop the DR detector and what will show up on the image because of it
-break glass
-break wires connecting readout circuit
-fracture crystals
-seperate scintillator from TFT
shows up as lines and patches missing
what does TFT stand for
thin-film transistor
what can happen if u let the DR detector get too hot
melts the glue binders
what happens if you overexpose a DR detector and why
burns out image as its so sensitive
missing data in the lower tissue thicknesses
what can happen to image if you let back scatter reach DR detector
shows reflected shadow of electrons or battery as its so sensitive
what can happen to the image if you expose the DR detector for too long or short at the correct mAs
too long = overstimulation and blue
too short = lines forming as not enough time to collect data
