Digital X-ray

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X-ray of the chest with its 2D Fourier spectrum

Digital X-ray encompasses radiological procedures in which X-ray images are no longer recorded on analog X-ray films , but digitally . Instead of the film, the devices contain a scintillator that converts incident X-ray photons either into visible light or directly into electricity. Older DR systems recorded the scintillation of the luminous layer optically reduced with a video camera , a CCD sensor or a CMOS chip. Today, to increase the spatial resolution, full-field detectors ( flat panel detectors ) are used which are at least as large as the X-ray image. They contain a luminous layer made of cesium iodide, a layer of microlenses, and a layer of photodiodes. Solid-state detectors made of rare earths such as gadolinium oxysulphide or amorphous selenium, which convert the X-ray photons that hit them directly into electricity without detour via visible light, have even better resolution and transfer them to the adjacent TFT layer. The data recorded in the detector are digitally passed on to a computer.

To retrofit older X-ray systems, there are photostimulable storage panels (PSP) made of special phosphorescent substances (barium fluoride halides). These X-ray imaging plates can be exposed like a film in exchangeable cassettes, transported and then “developed” in a reader, i.e. H. can be read out. The imaging plates hold the latent image for up to eight hours; For reading, they are scanned pixel by pixel with a He-Ne laser beam and the emitted light is measured. The spatial resolution of this scan is limited. Direct radiography systems are usually abbreviated as DR, and storage film systems as CR ( computed radiography ).

Digital X-ray has a better density contrast, but does not achieve the spatial resolution of film-foil X-ray (20 line pairs / mm). With CR systems, the spatial resolution is limited by the optical components used to approx. 2–5 line pairs / mm (exception: Fuji HQ system for mammography: 11 lp / mm and image plate scanner from Ditabis AG up to 20 lp / mm ( up to max. 15 µm)). DR systems range from pixel sizes around 200 μm to 50 μm corresponding to 10 Lp / mm. Their modulation transfer function is usually better than that of the CR systems.

Digital x-rays are usually only useful in conjunction with a radiology information system (RIS) and a digital image archiving system (PACS). The recordings can be saved and sent in DICOM format. In contrast to classic X-ray film , the digital images can easily be post-processed, e.g. B. by sharpening the edges or brightening, and the systems are much less sensitive to overexposure and underexposure, so fewer images have to be repeated. Modern DR consoles analyze the blackening histogram of the recording and, if necessary, correct the sensitivity and slope of the density curve afterwards. Artifact correction, hardening, and noise reduction are further options for image improvement. Unexposed edges are automatically cut off.

history

Eastman Kodak filed the first patent for digital x-ray in 1973. The first commercial CR solution was offered by Fujifilm in Japan in 1983 under the name CR-101. Other innovative manufacturers were Kodak and Agfa. In 2013 almost 70 manufacturers worldwide offered systems for digital radiography. X-ray image plates are used to record the shadow image of the X-ray radiation.

The first commercial digital X-ray system for use in dentistry was introduced in 1986 under the name Radiovisiography. Since then there have also been numerous manufacturers of digital X-ray systems in dentistry. The sensors are available in various bite-sized sizes.

Sources and individual references

  1. ↑ KK Chelliah, S. Tamanang et al. a .: A comparative study of computed radiography-based mammography using digital phosphor storage plate and full field digital mammography. In: Indian journal of medical sciences. Volume 67, Numbers 1-2, 2013 Jan-Feb, pp 23-28, ISSN  1998-3654 . doi : 10.4103 / 0019-5359.120694 . PMID 24178338 .
  2. ↑ LJ Kroft, WJ Veldkamp u. a .: Comparison of eight different digital chest radiography systems: variation in detection of simulated chest disease. In: American Journal of Roentgenology . Volume 185, Number 2, August 2005, pp. 339-346, ISSN  0361-803X . doi : 10.2214 / ajr.185.2.01850339 . PMID 16037503 .
  3. ^ Ulrich Bick, Felix Diekmann: Digital Mammography . Springer, March 11, 2010, ISBN 978-3-540-78450-0 , p. 9.
  4. ↑ George Luckey / Fa. Eastman-Kodak: Apparatus and method for producing images corresponding to patterns of high energy radiation. US 3859527 A (1975)
  5. ^ Eliot L. Siegel, Robert M. Kolodner: Filmless Radiology . Springer, January 1, 2001, ISBN 978-0-387-95390-8 , pp. 137-138.
  6. ^ Medical Expo, August 2013 ( Memento from August 26, 2013 in the Internet Archive )
  7. ↑ DGZMK Digital Radiography (PDF; 37 kB)