News and discussions about image sensors
Watch out Amorphous silicon panels! This sounds like a disruptive technology for that market.
What is the fundamental advantage compared to a-Si X-ray panel please ? From my understanding, this polymer photodiode needs thin-film transistor for readout. In this case, only if this polymer photodiode is much better than a-Si photodiode, otherwise the advantage is limited. Thanks !-yang ni
I would postulate that one advantage of OPDs for X-ray imaging appls. might be alternate scintillator-detector configurations - e.g. "back screen configuration" originally used in Screen-Film radiography -Here, the x-rays travel through the detector, excite the phosphor and the light is shone back onto the detector.For some X-ray energies, this would not be possible in TFTs, because the silicon and glass substrate would attenuate the signal too much, but the organic substrates would be much more transmissive
I suppose that if TFT can be done soft polymer substrate, then we can have a plexible X-ray detection sheet. That is very interesting in this case. Is this possible ? Thanks !-yang ni
Yang,We looked into this when I ran Varian's Imaging Systems group around 2000. Uniax had already made a line scan device using polymer photodiodes on glass and the first pentacene transistors had been fabricated. Mobility wasn't quite good enough but it is now. There was also a company (I can't remember the name now) setting up for roll-to-roll processing of amorphous silicon on plastic for displays. I haven't really evaluated the state of the technology in a while but it should now be possible to make all-polymer photodiode/TFT arrays on flexible substrates. Couple this with standard Gadox film intensifying screens and shoudl be possible to build extremely rugged radiographic and fluororscopic panels. My guess is that they don't exist largely due to the lack of the necessary infrastructure.
Thanks Dave so this precision ! I see that recently some dentists change to flexible phosphor plate which can be scanned by a laser scanner : http://velopex.com/en/product/apixia-digirex/My dentist told me that this flexible plate is about 50euros piece and the image quality is better than CMOS based X-ray sensor which he had before. Could you please comment ? Thanks !-yang ni
These are stimlulable phosphor plates that have been used for 20 years in computed radiography. Basically, the x-ray exposure lifts the electrons in the phosphor to one energy level where they get stuck and then the laser lifts them again to a level that results in photon emission, which is detected by a photomultiplier or a really good silicon photodiode. The tradeoff is that the images are not available until the plate is removed from the mouth and placed in the scanner. The dynamic range is probably better than CMOS. Dental CR has been around for about 15 years.Wikipedia is as good as anyplace to start if you want to read about CR - http://en.wikipedia.org/wiki/Computed_radiography.
Thanks Dave ! My dentist said that CMOS has local image distortion (probably due to FOP on the sensor) which is very troublesome in fine observation. Phosphor plate (which is new in dental use, it was a patent of Hitachi, if I remember well ...) has no distortion and also the resolution can be adjusted by laser scanning. It is also very flexible and comfortable. He told me that the CMOS sensor head has to be changed every 5 years for 5000 euros and the phosphor plate costs only 50 euros, so very competitive product any way. The scanner is expensive. -yang ni
The first CR patent (US 3,859,527) was issued in 1975 to George Luckey at Eastman Kodak. Fuji produced the first commercial CR product. If I rememeber correctly, the first dental CR scanner was put out by a company in California (whose name I can't remember) in the late 90s about the time that Lumisys came out with their full-size desktop scanner.
Dave, thanks so much for this information !!-yang ni
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