Radiographic imaging plate
The "radiographic imaging plate" (IP) or “photo-stimulable phosphor” is a film-like radiographic detector comprised of specifically designed phosphors that trap and store the radiation energy. The stored energy is stable until scanned with a laser beam, which releases the energy as luminescence ("photostimulated luminescence" (PSL) phenomenon). This phosphor technology, launched in its first application to the medical X-ray diagnostic field, begins to be used for radiography of cultural heritage artefacts. In practical, the Imaging Plate is a flexible image sensor in which bunches of very small crystals (grain size: about 5 µm) of photo-stimulable phosphor like barium fluorobromide BaFBr (Eu2+), are uniformly coated on a polyester support film. Exposure of samples with the Imaging Plate is performed in a manner similar to that of radiographic film. The imaging plate is housed in a special cassette and placed under the object to be examined and the X-ray exposure is made. Hence, instead of taking an exposed film into a darkroom for developing in chemical tanks or an automatic film processor, the imaging plate is run through a scanner equipped with a focused laser beam. The PSL released upon the laser is collected by a photomultiplier tube (PMT) through a light collection guide and is converted to electric signals, subsequently converted to digital signals of 8 to 16 bits, depending on the intended purpose. The digital image can then be viewed and/or enhanced using software such as contrast enhancement, brightness adjustment, filtration, zoom.
Imaging plates can theoretically be re-used thousands of times if they are handled carefully. An image can be erased by simply exposing the plate to a room-level fluorescent light. Most laser scanners automatically erase the image plate after laser scanning is complete. The imaging plate can then be re-used.
imaging plate; IP; photo-stimulable phosphor; écran photo-stimulable (Fr.); détecteur photo-stimulable (Fr.)
Resources and Citations
- R.H.Bossi, F. Iddings, G.C. Wheeler, P.O. Moore, Nondestructive testing handbook, vol 4, Radiographic testing, 3rd edition, Columbus OH, ASNT, (2002)