Clinical
Pixel perfect F
Barbara Lamb explores the issues that need to be considered in producing high-quality digital images in dental practice
or many years, dental practices have been working with X-ray film and the associated
processing chemicals. Quality assurance was well documented and was taught to undergraduate dental students and dental care professionals in training. Ongoing continuing
professional development of the dental team clarified how to deal with processing problems and so, over many years, the quality assurance of film images has improved with education. Digital imaging, with technology advancing in dental practices, has become more and more popular and a growing number of practices now work with digital systems. Quality assurance in relation
to monitors to view images and how to recognise and correct errors in the digital image production should now be part of a practice’s quality assurance programme. This aims to produce consistently high-quality images while keeping doses as low as reasonably practicable (ALARP). Practice quality assurance should be documented and audited. Many dental practices have
made the move to digital imaging, but not all dentists are happy with the resulting images. The two parts of this article seek to assist understanding of the issues concerned. The first part looks at some of the problems dental practices experience in recognising the problems with the resulting image and
40 Ireland’s Dental magazine
at possible ways to rectify them and the second part looks at the role computer systems can have in relation to the optimisation of digital images. There are two types of digital
image receptor, both of which capture a two-dimensional image of the three- dimensional patient. These are computed radiography (CR) photostimulable phosphor plates (PSPs) and direct digital radiography (DR) solid-state detectors (SSDs). There are approximately 256
shades of grey pixels, which together make up the finished digital image. The sensors are very sensitive to X-rays and so the exposure to the patient can sometimes be dramatically reduced compared to that used with conventional radiographic emulsion film.
Photostimulable phosphor plates Under a protection layer is a photosensitive phosphor plate (PSP). This absorbs and stores the X-ray energy. After exposure, the plate is
placed in a processor where it is scanned and the energy is released as light. This is detected by a photomultiplier and the image divided into pixels. A photomultiplier gives them a numerical value in relation to the intensity of the light released and the digital information is stored in the computer. The image can then be manipulated and displayed. PSPs are comparable in size
to a conventional X-ray film and are compatible with most film holders. They are patient friendly and are suitable for use
Cardboard bitewing tabs Fig 2
Fig 1
A bitewing image captured on a badly damaged photostimulable phosphor plate
on most individuals including children and elderly patients. The more radiation that hits the sensor the darker the image will be. The capturing of the image
is not instant, but it takes only a matter of seconds rather than the few minutes it takes to process an emulsion film. After the plate has been scanned, the
latent (invisible) image is then cleared by being exposed to light, either in the scanner or, less often nowadays, manually on a light box.
QUALITY ASSURANCE FOR PSPS
1. Surface marking The phosphor layer is delicate and very easily marked by any
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