Digital radiography

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.

Digital Radiography (DR) or (DX) is essentially filmless X-ray image capture. In place of X-ray film, a digital image capture device is used to record the X-ray image and make it available as a digital file that can be presented for interpretation and saved as part of the patient’s medical record. The advantages of DR over film include immediate image preview and availability, 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. The largest motivator for healthcare facilities to adopt DR is its potential to reduce costs associated with processing, managing and storing films. Typically there are two variants of digital image capture devices. These devices include Flat Panel detectors (FPDs), and High Density Line Scan Solid State detectors.

FPDs are classified in two main categories:

1. Indirect FPD's - Amorphous silicon (a-Si) is the most frequent type of FPD sold in the medical imaging industry today. Combining a-Si detectors with a scintillator in the detector’s outer layer, which is made from Cesium Iodide (CsI), or Gadolinium Oxysulfide (Gd2O2S), converts X-ray to light. Because the X-ray energy is converted to light, the a-Si detector is considered an indirect image capture technology. The light is then 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 (TFT’s) or by fiber coupled Charged Couple Devices (CCD’s). The image data file is sent to a computer for display where the X-ray technologist can determine whether the image is appropriate for the intended anatomy. Once the Technologist determines the image is appropriate it can be sent to the radiologist’s workstation or printed on film for interpretation.

2. Direct FPD's - Amorphous Selenium Flat Panel Detectors (a-Se) are known as “direct” detectors because X-ray photons are converted directly to charge. The outer layer of the flat panel in this design is typically a high voltage bias electrode. The bias electrode accelerates the captured energy from an X-ray exposure through the amorphous selenium layer. X-ray photons flowing through the selenium layer create electron hole pairs. These electron holes transit through the selenium based on the potential of the bias voltage charge. As the electron 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. The image data file is sent to a computer for display where the X-ray technologist can review the image and check positioning and if desired, transmit the image to the radiologist’s workstation for diagnosis.

A High Density Line Scan Solid State detector device is composed of a Photostimulable Barium Fluoro Bromide doped with Europium (BaFlBr:Eu) or Cesium Bromide (CsBr) phosphor. The phosphor detector records the X-ray energy during exposure and is scanned by a linear laser diode to excite the stored energy which is released and read out by a digital image capture array of Charge Coupled Devices (CCD’s). The image data file is transmitted to the X-ray technologist at a computer for review and then sent to the radiologist for further interpretation.

Note: this term is restricted to flat, two-dimensional imaging. For more advanced forms of three-dimensional calculated images, see Computed tomography.

Contents

Radiological examinations

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 focus on a small region of the oral-maxillofacial region and extraoral where the film or the sensor is outside the mouth and the purpose is to visualize the entire oral maxillofacial 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.

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.

Digital radiographic systems

Digital dental radiography comes in two forms: direct digital (sensors) that connect directly to the computer via USB and provide immediate images and indirect digital (photostimuable phosphor plates, or PSP) which are plates that after being radiated can be scanned into a computer's imaging software via a special scanner.

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, however, following the introduction of CMOS imagers by Schick Technologies in early 1998/9, the vast majority of the industry introduced their own CMOS sensors between 2003 and 2010.

Indirect digital (a.k.a. PSP—Photostimulable Phosphor) 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 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. PSP has been described as having an advantage to be able to fit within any pre-existing equipment without modification because it replaces just the existing film, however this fails to take into account the need to invest in the scanner itself, as well as the need to replace the plates as they become scratched.

Also, sometimes the term "Digital X-rays" is used to designate the scanned film documents which are handled by further computer processing.


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 using the Kodak name which is used under license by Carestream (Canada). Trophy has released a wireless version of their RVG Intra-Oral sensor named the RVG 6500.
1992 - Sens-a-Ray of Regam Medical System AB (Sundsvall, Sweden) is first offered. The company went out of business and their technology was purchased by Dent-X, recently renamed as ImageWorks (USA).
1993 - VisualX of Gendex-Italy (subsidiary of USA company).
1994 - CDR of [Schick Technologies] http://www.schicktech.com (USA). Schick were the first company to offer 3 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)

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 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 C system.

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.

See also

Carestream Trophy has released an Intra-Oral Digital Radiography Sensor using WiFi connectivity. http://www.dentaleconomics.com/index/display/article-display/2376226487/articles/dentisryiq/products/technology/2011/02/carestream-debuts.html

External links


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