Digital radiography

Digital radiography is a form of radiography that uses x-ray–sensitive plates to directly capture data during the patient examination, immediately transferring it to a computer system without the use of an intermediate cassette. [1]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. This 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 quality of the image.

Detectors

Flat panel detectors
Flat panel detector used in digital radiography

Flat panel detectors (FPDs) are the most common kind of direct digital detectors.[2] They are 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.[3]

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.[3][4]

Other direct digital detectors

Detectors based on CMOS and charge coupled device (CCD) have also been developed, but despite lower costs compared to FPDs of some systems, bulky designs and worse image quality have precluded widespread adoption.[5]

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.

Phosphor plate radiography

Phosphor plate radiography[6] resembles the old analogue system of a light sensitive film sandwiched between two x-ray sensitive screens, the difference being the analogue film has been replaced by an imaging plate with photostimulable phosphor (PSP), which records the image to be read by an image reading device, which transfers the image usually to a Picture archiving and communication system (PACS).[6] It is also called photostimulable phosphor (PSP) plate-based radiography or computed radiography[7] (not to be confused with computed tomography which uses computer processing to convert multiple projectional radiographies to a 3D image).

After X-ray exposure the plate (sheet) is placed in a special scanner where the latent image is retrieved point by point and digitized, using laser light scanning. The digitized images are stored and displayed on the computer screen.[7] Phosphor plate radiography 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.

Initially phosphor plate radiography was the system of choice; early DR systems were prohibitively expensive (each cassette costs £40-£50K), and as the 'technology was being taken to the patient', prone to damage.[8] Since there is no physical printout, and after the readout process a digital image is obtained, CR has been known as an indirect digital technology, bridging the gap between x-ray film and fully digital detectors.[9][10]

Industrial usage

Security
EOD (Explosive Ordnance Disposal) training and material testing. A 105 mm shell is radiographied with battery powered portable X-ray generator and flat panel detector.

Digital radiography (DR) has existed in various forms (for example, CCD and amorphous Silicon imagers) in the security X-ray inspection field for over 20 years and is steadily replacing the use of film for inspection X-rays in the Security and nondestructive testing (NDT) fields.[11] DR has opened a window of opportunity for the security NDT industry due to several key advantages including excellent image quality, high POD (probability of detection), portability, environmental friendliness and immediate imaging.[12]

Materials

Nondestructive testing of materials is vital in fields such as aerospace and electronics where integrity of materials is vital for safety and cost reasons.[13] Advantages of digital technologies include the ability to provide results in real time.[14]

History
Direct x-ray imaging system (DXIS) - real time display

Key developments
1983Phosphor stimulated radiography systems first brought into clinical use.[15][16][17]
1987Digital radiography in dentistry first introduced as "RadioVisioGraphy".[18]
1995French company Signet introduce the first dental digital panoramic system.[19]
First amorphous silicon and amorphous selenium detectors introduced.[20][21]
2001First commercial indirect CsI FPD for mammography and general radiography made available.[22]
2003Wireless CMOS detectors for dental work first made available by Schick Technologies.[23]

See also

References
Library resources about
Digital radiography
  1. Marchiori, Dennis M. Clinical Imaging: with Skeletal, Chest, and Abdominal Pattern Differentials. Elsevier Mosby, 2014.
  2. Neitzel, U. (17 May 2005). "Status and prospects of digital detector technology for CR and DR". Radiation Protection Dosimetry. 114 (1–3): 32–38. doi:10.1093/rpd/nch532. PMID 15933078.
  3. Lança, Luís; Silva, Augusto (2013). "Digital Radiography Detectors: A Technical Overview". Digital imaging systems for plain radiography. New York: Springer. pp. 14–17. doi:10.1007/978-1-4614-5067-2_2. hdl:10400.21/1932. ISBN 978-1-4614-5066-5.
  4. Ristić, Goran S (2013). "The digital flat-panel X-Ray detectors" (PDF). Third Conference on Medical Physics and Biomedical Engineering, 18-19 Oct 2013. Skopje (Macedonia, The Former Yugoslav Republic of). 45 (10): 65–71.
  5. Verma, BS; Indrajit, IK (2008). "Impact of computers in radiography: The advent of digital radiography, Part-2". Indian Journal of Radiology and Imaging. 18 (3): 204–9. doi:10.4103/0971-3026.41828. PMC 2747436. PMID 19774158.
  6. Benjamin S (2010). "Phosphor plate radiography: an integral component of the filmless practice". Dent Today. 29 (11): 89. PMID 21133024.
  7. Rowlands, JA (7 December 2002). "The physics of computed radiography". Physics in Medicine and Biology. 47 (23): R123–66. doi:10.1088/0031-9155/47/23/201. PMID 12502037.
  8. Freiherr, Greg (6 November 2014). "The Eclectic History of Medical Imaging". Imaging Technology News.
  9. Allisy-Roberts, Penelope; Williams, Jerry R. (2007-11-14). Farr's Physics for Medical Imaging. Elsevier Health Sciences. p. 86. ISBN 978-0702028441.
  10. Holmes, Ken; Elkington, Marcus; Harris, Phil (2013-10-10). Clark's Essential Physics in Imaging for Radiographers. CRC Press. p. 83. ISBN 9781444165036.
  11. Mery, Domingo (2015-07-24). Computer Vision for X-Ray Testing: Imaging, Systems, Image Databases, and Algorithms. Springer. p. 2. ISBN 9783319207476.
  12. "A Review of Digital Radiography in the Service of Aerospace". Vidisco. Retrieved 2012-09-27.
  13. Hanke, Randolf; Fuchs, Theobald; Uhlmann, Norman (June 2008). "X-ray based methods for non-destructive testing and material characterization". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 591 (1): 14–18. doi:10.1016/j.nima.2008.03.016.
  14. Ravindran, V R (2006). Digital Radiography Using Flat Panel Detector for the Non-DestructiveEvaluation of Space Vehicle Components (PDF). National Seminar on Non-Destructive Evaluation. Hyderabad: Indian Society for Non-Destructive Testing.
  15. Sonoda, M; Takano, M; Miyahara, J; Kato, H (September 1983). "Computed radiography utilizing scanning laser stimulated luminescence". Radiology. 148 (3): 833–838. doi:10.1148/radiology.148.3.6878707. PMID 6878707.
  16. Bansal, G J (1 July 2006). "Digital radiography. A comparison with modern conventional imaging". Postgraduate Medical Journal. 82 (969): 425–428. doi:10.1136/pgmj.2005.038448. PMC 2563775. PMID 16822918.
  17. Mattoon, John S; Smith, Carin (2004). "Breakthroughs in Radiography Computed Radiography". Compendium. 26 (1).
  18. Frommer, Herbert H.; Stabulas-Savage, Jeanine J. (2014-04-14). Radiology for the Dental Professional - E-Book. Elsevier Health Sciences. p. 288. ISBN 9780323291156.
  19. Nissan, Ephraim (2012-06-15). Computer Applications for Handling Legal Evidence, Police Investigation and Case Argumentation. Springer Science & Business Media. p. 1009. ISBN 9789048189908.
  20. Zhao, Wei; Rowlands, J. A. (October 1995). "X-ray imaging using amorphous selenium: Feasibility of a flat panel self-scanned detector for digital radiology". Medical Physics. 22 (10): 1595–1604. doi:10.1118/1.597628. PMID 8551983.
  21. Antonuk, L E; Yorkston, J; Huang, W; Siewerdsen, J H; Boudry, J M; el-Mohri, Y; Marx, M V (July 1995). "A real-time, flat-panel, amorphous silicon, digital x-ray imager". RadioGraphics. 15 (4): 993–1000. doi:10.1148/radiographics.15.4.7569143. PMID 7569143.
  22. Kim, H K; Cunningham, I A; Yin, Z; Cho, G (2008). "On the development of digital radiography detectors: A review" (PDF). International Journal of Precision Engineering and Manufacturing. 9 (4): 86–100.
  23. Berman, Louis H.; Hargreaves, Kenneth M.; Cohen, Steven R. (2010-05-10). Cohen's Pathways of the Pulp Expert Consult. Elsevier Health Sciences. p. 108. ISBN 978-0323079075.
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