Photostimulable phosphors (PSP) are materials that store absorbed energy within excited electrons and release it in the form of light on exposure to laser energy.
The process can be broken up as follows :
PSPs are used to record and reproduce a latent x-ray image by absorbing the radiation, then releasing the stored energy as light photons when stimulated by a HeNe laser. The emitted photons are detected by a photomultiplier tube, and an electronic signal is produced which is converted to a digital image for viewing on PACS .
PSP materials are crystal lattices, which give near uniform characteristics to electron bands, and impurities, which alter the electron bands to induce electron traps in the forbidden zone. One of the materials of choice is barium fluorobromide doped with europium (2+ valence), however many others exist with their own unique properties.
The material itself needs certain properties to satisfy a number of criteria in order for it to be useful in image acquisition:
- release the stored energy when exposed to a wavelength produced by common lasers
- release the stored energy in a photon wavelength readily absorbed by common photomultiplier tubes
- retain the latent image without significant signal loss over time due to phosphorescence