The PMT produces an amplified voltage proportional to the original light received. The blue light is detected by a photomultiplier tube (PMT). This process is known as “photostimulable luminence”. The laser energy causes the electrons to fall back into the europium holes, emitting light from the blue part of the visible spectrum. The PSP with the stored latent image is scanned immediately using a thin red helium–neon laser beam. Scanning the PSP and Displaying the Image The number of trapped electrons at any particular point on the PSP is proportional to the original number of x-ray photons incident on that part of the sensor, thus producing a latent image. Some of the electrons drop back almost immediately, but importantly, the remaining electrons stay trapped within the F centres. These electrons become trapped within fluorohalides at sites known as “F centres”, leaving “holes” at the original europium sites. When exposed to x-radiation, photoelectric interactions within the phosphor layer produce photoelectrons, which remove electrons from the europium activator. Interaction of the Phosphor Layer with X-radiation A PSP will last for several thousand exposures, so long as it remains undamaged and free of scratches.įig 7-1 Cross section through a typical PSP showing the layers and their functions.
The PSP is similar for all systems and comprises:Ī cross section of a PSP illustrating these layers and their functions is shown in Fig 7-1. Principles of Indirect Digital Radiography Construction of the PSP As there is this additional scanning process, these systems are referred to as indirect digital systems. With these systems, once the PSP has been exposed the sensor has to be scanned by a laser before the image can be displayed. In this chapter, the term is used for images acquired using a photostimulable phosphor plate (PSP). To some this means digitising a conventional radiograph using a flatbed scanner with a transparency adaptor. There is some confusion in the use of the term “indirect digital imaging”. What Does Indirect Digital Radiography Mean? Give the advantages and disadvantages of these systems.
OutcomeĪfter reading this chapter the reader should be able to:ĭescribe the basic construction of a photostimulable phosphor plateĮxplain how a typical indirect digital system works The aim of this chapter is to provide a comprehensive understanding of indirect digital x-ray imaging in dentistry.
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