Digital Imaging receptors (intro) Flashcards
what is CR
computed radiography
what is DR
Digital radiography
what principle does CR use
photostimulable luminescence to produce an image
what is the most popular phosphor material used
barium flurohalide
what is luminescence
when CR receptors use light photons to produce an image using a material that has the property of ‘glowing’ when it is irradiated
what happens in CR when it is subjected to x-ray photon energy
the phosphor plate gives a small amount of light, but stores most of the energy. The latent image remains stable for a period of time but will eventually deteriorate
how does the infra red laser beam work
it scans the surface of the phosphor plate in a raster pattern while the plate moves slowly forward. The light emitted from each point is proportional in intensity to the number of x-ray photons absorbed at that point. The light emitted is focussed by an optical system of lenses and mirrors. this light is shielded from the original laser light which is many times brighter
what happens to the emitted light in CR
it is collected by a photomultiplier tube in a reader and converted to varying electrical signals. These signals are amplified, sampled and passed through ADC (analogue digital converter) to produce binary values for the brightness of each pixel
Digital image is now available for post processing
what are the two formats in DR
1) indirect DR (IDR)
2) Direct DR (DDR)
what happens in indirect digital receptors
they convert x-ray photons to light in the intermediate stage within the detector itself
in IDR what absorbs x-ray photons and what does it convert them into
caesium iodide scintillator converts them to light and channels them to a photodiode array
what does the photodiode array consist of
amorphous silicon panels. each photodiode represents a pixel
what are light photons converted into in IDR
an electronic charge
what are TFT’s and what do they do
Thin Film Transistors act as electronic switches in this array
what is the charge at each TFT read out by
low noise electronics and converted to digital data which is sent to an image processor
