X-ray imaging plate

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X- ray imaging foils are used in X-ray diagnostics to record the shadow image of the X-ray radiation. They are increasingly replacing the conventional, silver halide- based X-ray films because they are recyclable. The image plates are usually delivered in a cassette design and are therefore compatible with the film cassettes in terms of their dimensions, so that existing X-ray machines do not have to be converted. Since the latent images are read out pixel by pixel with a reader, digital X-ray images are always created .

construction

The image plates are made up of layers of plastic and a 0.1-0.2 mm thick fluorescent layer (doped barium fluoride ) and are flexible. The luminescent material stores the intensity of the X-ray radiation that has arrived by exciting the luminescent layer and shifting doping atoms to interstitial spaces. In the reader, the film is removed from the cassette and scanned line by line with a laser with a wavelength of 500–700 nm. The photoluminescence is supplied to each pixel with a photomultiplier detected in a number converted and stored. The readout process is shorter than conventional film processing.

Useful life

In theory, each film can be reused up to 10,000 times. In everyday clinical practice, however, mechanical wear and tear limits the useful life of the imaging plates through abrasion, scratches and kinks, because each of these surface changes becomes visible in all subsequent X-ray images. With imaging plates in dentistry, which are positioned in a protective film directly in the mouth, under these harsh conditions, even with careful use, at most a few hundred images can be made before they have to be replaced.

Image processing

Image plate cassettes usually have a barcode on them so that the computer can associate the image with the correct patient. The recording is usually sent to a work console via the local network. The radiology assistant can edit the image there. This includes rotating the images, changing the contrast, adding comments and right and left symbols. Underexposure and overexposure can be compensated to a certain extent by changing the virtual "sensitivity". The brightness area that contains the greatest contrast is intensified. Several images are combined into a series and sent to the PACS in DICOM format .

The readout process should take place at the latest one hour after the exposure, because the stored X-ray information is permanently degraded. About 50% of the information is lost after 24 hours. The latent image on the phosphor layer is then erased in the reader by exposing it to normal light. Since the deletion can never be complete, persistent shadow images remain that theoretically overlap a subsequent exposure, which is insignificant in practice due to the exposure conditions.

Formats

The most common formats are like conventional X-ray film

  • 2 × 3 cm (small tooth film for children)
  • 3 × 4 cm (large tooth film for adults)
  • 5 × 6 cm (dental film for bite exposures)
  • 18 × 24 cm
  • 18 × 43 cm
  • 20 × 40 cm
  • 24 × 30 cm
  • 35 × 35 cm (14 × 14 inches)
  • 35 × 43 cm (14 × 17 inches)
  • 15 × 30 cm
  • 20 × 25 cm (8 × 10 inches)
  • 25 × 30 cm (10 × 12 inches)

Common reading devices (multi-format readers) can usually read all formats. The readout speed of the readers is between 20 and 190 image plates per hour, depending on the format used. The resolution of X-ray imaging plates and reading devices is approx. 6-15 pixels per millimeter. In digital mammography , up to 20 pixels per millimeter are achieved.

X-ray storage foils have recently been increasingly being replaced by solid-state detectors . Due to their robustness and the possibility of retrofitting existing X-ray devices, as well as their low price, they will probably find more widespread use in the future. A reader costs between € 60,000 and € 120,000, depending on the equipment and necessary additional services (installation, maintenance contract) - small devices for the dental sector are available for less than 10,000.

swell

  • Theodor Laubenberger, Jörg Laubenberger: Technology of medical radiology: diagnostics, radiation therapy, radiation protection. For doctors, medical students and MTRA . Deutscher Arzte-Verlag, Germany 1999, ISBN 3-7691-1132-X .
  • Eliot L. Siegel, Robert M. Kolodner: Filmless Radiology . Springer, December 12, 2001, ISBN 978-0-387-95390-8 .

Web links

Individual evidence

  1. ^ P. Monnin, D. Gutierrez, S. Bulling, D. Guntern, FR Verdun: A comparison of the performance of digital mammography systems. In: Medical physics Volume 34, Number 3, March 2007, pp. 906-914, ISSN  0094-2405 . PMID 17441236 .