Digital imaging basics

Using imaging plates it is possible for a dentist to get very accurate digital x-ray images of patients’ teeth. Digital images differ from traditional images in the way the image is built. Digital images are pure data that is interpreted by the computer into a visual representation of the data: a picture. The data includes information on the color of every pixel (picture element). In black and white pictures this information is basically the shade of gray that the pixel is. Bit depth is the range of grays that can be recorded and displayed. In 8-bit images there are 256 shades of gray which already very sufficient for dental diagnostics, not to mention 16-bit images that have over 65000 shades. Most digital x-ray imaging systems have displays that can only show 256 shades so 8-bit depth is usually sufficient.

The image data in intraoral imaging is collected with an imaging plate. The plate is exposed to radiation in a similar manner to film. The plate can detect radiation because of a layer of small photo-stimulable crystals on its surface that are excited to a different state by the radiation. The exposed image plate is then scanned with laser which causes the plate to release light, which is then collected and converted to analog electric signals and further into digital signals, which can then be displayed on a monitor and analyzed and enhanced when necessary.

This new solution has changed the way small practices can treat patients. Image quality is measured with many different metrics. Dynamic range is the sensitivity of the imaging plate to exposure. A wide dynamic range allows for more shades of gray and reduces the amount of over- or underexposure in pictures. Signal-to-noise ratio is also important in high quality pictures. Noise reduces image quality by introducing unwanted information to the picture making them grainy. This causes inaccuracy in images and lowers their validity. Keeping the noise-to-signal ratio low, while maintaining a good contrast and dynamic range, is one of the biggest challenges of digital dental imaging.

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