Introduction

SPPs include a reusable photostimulated screen, a readout scanner, a photomultiplier tube, a digital interface card, a computer, and software.  When x-ray photons strike the phosphor layer included on the plate, a latent image is formed.  The phosphor screen releases the stored energy as light photons when scanned by the readout device by means of photostimulation.  The intensity of the light emitted is proportional to the x-rays absorbed by the plate.  The photomultiplier tube is used to convert small amounts of light into an amplified electric signal.¹⁰  The resulting signal is digitized by an analog-to-digital converter (ADC), which determines the number of shades of gray in the image.

The main advantages of both CCD sensors and SPPs include reduction in radiation dose to the patient and availability of a variety of image enhancements.  CCD sensors offer more rapid image acquisition.  Cost of the equipment, stiffness of the sensor, and presence of a cord attachment between the sensor and computer are the main drawbacks of the CCD sensors.  SPPs demonstrate wider exposure latitude than do CCD sensors.  Flexibility of these plates and absence of an electrical cord are other advantages.  The primary disadvantage of SPPs is the need for additional time to readout the image.¹¹  The need for a readout device to scan the plates adds to the cost of the system.  Also, plates must be exposed to light to erase the residual image before reusing them.  Lastly, the resolution of storage phosphor images is reduced compared to CCD images since their pixel size is slightly larger.¹¹  Despite advancements in digital radiography, the resolution of digital images in general is still lower than radiographic film.¹²

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Citation Number: Vol. 5, No. 2, Page 059