Chapt. 25 Computed Radiography Digital terms are NOT uniform, but vary from one brand to the next!

DR introduced in 1981 Fuji introduced “digital imaging” in 1981 –Many forms of digital CR DR

CR Terms PSL= photostimulable luminescence PSP=photostimulable phosphore SPS=storage phosphor screen IP=imaging plate SP=storage phosphore PMT=photomultiplier tube PD=photodiode

PSL & PSP Photostimulable luminescence (PSL) –Emit light promptly AND at a later time! Photostimulable phosphor (PSP) – barium fluorohalide looks physically like an intensifying screen BUT stores the latent image via metastable electrons (STORAGE PHOSPHOR SCREENS) SPSs

The “imaging plate” The PSP screen is inside a “rigid” (not really as they are brittle and do break easily – much more so than film/screen cassettes) cassette The actual imaging receptor is called the IMAGING PLATE

Light Stimulation Emission Process similar to Thermosluminescent dosimetry (TLD – film type badges for dosimetry) They are either “powder” (like an intensifying screen crystal) OR arranged like “needles” i.e. Powder PSP or Needle PSP

Thoughts on PSP’s Powder vs “needle” Highly sensitive to RADIATION = easily fogged!!!

CR Reader The physical receptor - cassette is “loaded” into the reader –IP is removed and moves along the LONG AXIS of the IP!!! (slow scan) –As the IP is moved, a deflection device is used to deflect the LASER beam across the IP (fast scan) IP doesn’t really separate from the cassette and doesn’t go around “rollers” etc.

CR Optical feature To properly and precisely translate EACH metastable electron (latent image forming charge) in a PRECISE fashion to provide for great SPATIAL RESOLUTION

Compare and contrast film-screen to CR techniques Film- screen has much LOWER latitude than CR!!! –As such – a WIDE variety of techniques can be used = Burn em up BURNIE!!!! If in doubt – “BURN IT OUT” Compare Characteristic curves for each:

Image noise Box 25-1 SAME as screen-film noise PLUS Box 25-2 –Mechanical defects – due to the scan drivers –Optical defects – laser, stimulating beam, light quanta emission and collected –Computer defects – electronic noise; too few sampling; too little quantization