Digital radiography
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Digital radiography is a form of x-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also less radiation can be used to produce an image of similar contrast to conventional radiography.
Note: this term is restricted to flat, two-dimensional imaging. For more advanced forms of three-dimensional calculated images, see Computed tomography.
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[edit] Radiological examinations
[edit] Dental
The radiological examinations in dentistry may be classified in: intraoral - where the film or the sensor is placed in the mouth, the purpose being to visualize a limited region and extraoral where the film or the sensor is outside the mouth and the purpose is to visualize a wide region. In dentistry, extraoral imaging splits in: Panoramic X-ray (aka "panorex" or "pano") showing a section, curved following more or less mandible shape, of the whole maxillo-facial block and the Cephalometric X-ray showing a projection, as parallel as possible, of the whole skull.
[edit] Digital radiographic systems
One particular type of digital system uses a Memory Phosphor Plate (a.k.a. PSP -- Photostimulable Phosphor) in place of the film. After X-ray exposure the plate (sheet) is placed in a special scanner where the latent formed image is retrieved point by point and digitized, using laser light scanning. The digitized images are stored and displayed on the computer screen. This method is halfway between old film-based technology and current direct digital imaging technology. It is similar to the film process because it involves the same image support handling but differs because the chemical development process is replaced by the scanning process. This is not much faster than film processing and the resolution and sensitivity performances are contested. However, it has the clear advantage to be able to fit within any pre-existing equipment without modification because it replaces just the existing film.
Also, sometimes the term "Digital X-rays" is used to designate the scanned film documents which are handled by further computer processing.
Other types of digital imaging technologies use electronic sensors. A majority of them first convert the X-rays into visible light (using a GdO2S or CsI layer), which is further captured using a CCD or a CMOS image sensor. Some of them use a hybrid arrangement which first converts the X-rays into electricity (using a CdTe layer) and then captures this electricity as an image with a reading section based on CMOS technology.
[edit] Historical milestones for Digital Intraoral Sensors
1987 - RVG, the world wide first intraoral X-rays imaging sensor available on the market, introduced by Trophy Radiology (France) was very quickly and largely recognized by the European dental market. This company is owned actually by Kodak and continues to produce intraoral sensors.
1992 - Sens-a-Ray of Regam (Finland) is offered. They closed the business and their technology is currently owned by Dent-X (USA).
1993 - VisualX of Gendex-Italy (subsidiary of USA company).
1994 - CDR of Schick Technology (USA). Also Schick Technology introduced last years a wireless CDR version being the only supplier offering such feature. This company is owned actually by Sirona (Germany).
1995 - SIDEXIS of Sirona, DEXIS of ProVison Dental Systems, Inc. (renamed DEXIS, LLC following its acquisition by Danaher Corp.), DIGORA (PSP solution) of Soredex (Finland)
Today there are many other products available under a lot of different names (rebranding is quite usual for this type of product)
The manufacturers claim the resolution is between 12 to 25 LP/mm. A useful precise comparison is difficult because depends on many parameters including the post processing or imaging software. ==
Historical milestones for Digital Panoramic Systems
- 1995 - DXIS, the world wide first dental digital panoramic X-rays system available on the market, introduced by Signet (France). DXIS targets to retrofit all the panoramic models.
- 1997 - SIDEXIS, of Siemens (currently Sirona, Germany) offered for Ortophos Plus panoramic unit, DigiPan of Trophy Radiology (France) offered for the OP100 panoramic made by Instrumentarium (Finland).
- 1998-2004 - many panoramic manufacturers offered their own digital system.
- 2005 - SCAN300FP, of Ajat (Finland) is the last one offered. It shows the feature to acquire many hundreds of mega bytes of image information at high frame rate and to reconstruct the panoramic layer by intensive post acquisition computing like a computed tomography. The main advantage is the ability to reconstruct focused differently. The drawback is the low signal/noise ratio of primary information which involves much software work for correction. Also the ability to reconstruct various layers raises the importance of the geometrical distortions already high in dental panoramic radiography.
Currently there are several digital systems for panoramic digital radiology. Some of them are rebranded. Examples: SCAN300FP of Ajat was or is sold as SuniPan or RetroPan or Panoramic Corporation pan, DXIS of Signet was or is sold also as of LightYear, Sigma Biomedics, Panoramic Corporation, AFP Digital or Bluex, iPan of Schick was or is sold as of Bluex or Panoramic Corporation, I-MAX of Owandy sold as of Villa, etc.
