HINTON, EDSON, JASPER, ALBERTA - In digital radiography, a sensor replaces the film normally used for traditional radiographs. The sensor plugs into the USB port on an ordinary computer. The most common type of Intraoral sensors are solid-state electronic devices called “charged-coupled devices” (CCD). A CCD is composed of millions of light sensitive silicon cells arranged in a rectangular array on the face of the sensor. Each cell on the face of the sensor will eventually result in one pixel (picture element) in the final image.
The digital xray photons falling upon each cell create an analog (continuous) electrical voltage. The level of the voltage produced depends on the number of photons reaching the cell, and this in turn depends on the density of the structures (teeth and bone) between the x-ray source and the CCD. The voltage level for each pixel is converted to digital data (numbers between 0 and 65,536) by a relatively simple device called an "analog to digital converter". Each value is interpreted by the computer as a shade of gray. Zero corresponds to pure white, and 65,536 corresponds to pure black with intermediate values corresponding to varying shades of gray. In this way, the image is converted to millions of tiny digital picture elements (pixels) which are reassembled by the computer into a coherent image.
CCD's used in dental imaging are essentially the same as the CCD's used in digital cameras. In your home camera, the CCD contains color filter arrays for each pixel so the image can be reassembled in color. Since dental radiographs are monochrome (shades of gray), the dental CCD does not contain these filters
While digital radiography is a newer technology than the film it replaces, it must be stressed that the image obtained on a digital xray is not necessarily any better than one taken using standard x-ray film. Digital technology does, however, require substantially less radiation than film. Digital radiography requires only about a quarter as much exposure time as D speed film, and a little more than half the time as the newest F-speed films, while delivering about the same resolution as D speed film.
The largest benefit of digital xray is the ability to computer-enhance the images, making them larger, clearer, or higher contrast at will. This can be helpful, particularly for dentists with less experience in reading traditional film, but it is rarely essential in making a correct diagnosis. Larger, sharper images are helpful in patient education and in helping patients to accept a treatment plan. There is no darkroom developing of the images, and the sensor can be moved about in the mouth more quickly than films, which must be exchanged for new ones for each shot. Thus digital radiography cuts down on the time it takes to expose and process a series of intraoral films. For these reasons, digital radiography is gaining increasing acceptance in dental offices throughout the US and Europe.
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