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Digital Radiography

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.

Instead of X-ray film, digital radiography uses a digital image capture device. The gives advantages of immediate image preview and availability; elimination of costly film processing steps; a wider dynamic range, which makes it more forgiving for over- and under-exposure; as well as the ability to apply special image processing techniques that enhance overall display of the image.



[edit] Detectors

There are two major variants of digital image capture devices: flat panel detectors (FPDs) and high-density line-scan solid state detectors. FPDs are further classified in two main categories:

1. Indirect FPDs. Amorphous silicon (a-Si) is the most common material of commercial FPDs. Combining a-Si detectors with a scintillator in the detector’s outer layer, which is made from caesium iodide (CsI) or gadolinium oxysulfide (Gd2O2S), converts X-rays to light. Because of this conversion the a-Si detector is considered an indirect imaging device. The light is channeled through the a-Si photodiode layer where it is converted to a digital output signal. The digital signal is then read out by thin film transistors (TFTs) or fiber-coupled CCDs. The image data file is sent to a computer for display.

2. Direct FPDs. Amorphous selenium (a-Se) FPDs are known as “direct” detectors because X-ray photons are converted directly into charge. The outer layer of the flat panel in this design is typically a high-voltage bias electrode. X-ray photons create electron-hole pairs in a-Se, and the transit of these electrons and holes depends on the potential of the bias voltage charge. As the holes are replaced with electrons, the resultant charge pattern in the selenium layer is read out by a TFT array, active matrix array, electrometer probes or microplasma line addressing.

A high-density line-scan solid state detector is composed of a photostimulable barium fluorobromide doped with europium (BaFBr:Eu) or caesium bromide (CsBr) phosphor. The phosphor detector records the X-ray energy during exposure and is scanned by a laser diode to excite the stored energy which is released and read out by a digital image capture array of a CCD.

[edit] Radiological examinations

[edit] Dental

Main article: Dental radiography

The radiological examinations in dentistry may be classified into intraoral – where the film or sensor is placed in the mouth, the purpose being to focus on a small region of the oral-maxillofacial region and extraoral where the film or sensor is placed outside the mouth aiming to visualize the entire oral maxillofacial region. Extraoral imaging is further divided into orthopantomogram, showing a section, curved following more or less mandible shape, of the whole maxillofacial block and cephalometric analysis showing a projection, as parallel as possible, of the whole skull.

Digital radiography in dentistry provides the clinician with the ability to store their images on a computer. This provides two key advantages over film in the form of full screen images that can be enhanced and zoomed in on, aiding diagnostics and providing easier patient communication, as well as allowing dental offices to communicate images electronically, allowing for simpler referrals and, where applicable, easier insurance claim submission.

[edit] Digital radiographic systems

Digital dental radiography comes in two forms: direct, that connect directly to the computer via USB and provides immediate images, and indirect (photostimulable phosphor plates, or PSP) which uses plates that are radiated and then digitally scanned.

Direct digital sensors represent a significant initial investment, but in addition to the convenience of digital images, provide instant images that can reduce the time the patient spends in the dental chair. They also reduce the need for the constant purchase of film and the necessary development chemicals. Early systems used CCD sensor technology, but changed to CMOS sensors following their introduction in early 1998-9.

Indirect digital imaging utilizes a reusable plate 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 in that the chemical development process is replaced by scanning. This is not much faster than film processing and the resolution and sensitivity performances are contested. PSP has been described as having an advantage of fitting within any pre-existing equipment without modification because it replaces the existing film; however, it includes extra costs for the scanner and replacement of scratched plates.

[edit] Historical milestones for digital intraoral sensors

  • 1987 – RVG (radiovisiography), Trophy Radiology (France) introduced the world’s first intraoral X-rays imaging sensor. Trophy Radiology patented it under the restricted name radiovisiography (other companies use the phrase digital radiography) and continues to produce intraoral sensors today under the Kodak name, which is used under license by Carestream (Canada). Trophy has released a wireless version of their RVG intraoral sensor named the RVG 6500.
  • 1992 – Sens-a-Ray of Regam Medical System AB (Sundsvall, Sweden) is introduced. The company went out of business and their technology was purchased by Dent-X, recently renamed to ImageWorks (USA).
  • 1993 – VisualX of Gendex-Italy (subsidiary of USA company).
  • 1994 – CDR of Schick Technologies, USA. Schick were the first company to offer three film-like sizes of sensor, as well providing the significant breakthroughs of CMOS-APS technology (1998), USB connectivity (1999), the first sensors without cables (2003) and the first sensors with replaceable cables (2008). They launched their second generation of CMOS-APS chips in 2009. Schick merged with Sirona (Germany) in 2006 and is now part of Sirona Dental Systems, LLC.
  • 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).

[edit] Historical milestones for digital panoramic systems

  • 1995 – DXIS, the first dental digital panoramic X-rays system was 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 latest innovation 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. Since 2008 the SCAN300FP system is available in Ajat ART PLUS and ART PLUS Csystem
    From Wikipedia, the free encyclopedia

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