flat-panel detector

File:Resolution in direct and indirect x-ray detectors.svg

X-rays pass through the subject being imaged and strike one of two types of detectors.

Indirect detectors contain a layer of scintillator material, typically either gadolinium oxysulfide or cesium iodide, which converts the x-rays into light. Directly behind the scintillator layer is an amorphous silicon detector array manufactured using a process very similar to that used to make LCD televisions and computer monitors. Like a TFT-LCD display, millions of roughly 0.2 mm pixels each containing a thin-film transistor form a grid patterned in amorphous silicon on the glass substrate.{{cite journal|last1=Kump|first1=K|last2=Grantors|first2=P|last3=Pla|first3=F|last4=Gobert|first4=P|title=Digital X-ray detector technology|journal=RBM-News|date=December 1998|volume=20|issue=9|pages=221–226|doi=10.1016/S0222-0776(99)80006-6}} Unlike an LCD, but similar to a digital camera's image sensor chip, each pixel also contains a photodiode which generates an electrical signal in proportion to the light produced by the portion of scintillator layer in front of the pixel. The signals from the photodiodes are amplified and encoded by additional electronics positioned at the edges or behind the sensor array in order to produce an accurate and sensitive digital representation of the x-ray image.{{cite journal|last1=Kotter|first1=E.|last2=Langer|first2=M.|title=Digital radiography with large-area flat-panel detectors|journal=European Radiology|date=19 March 2002|volume=12|issue=10|pages=2562–2570|doi=10.1007/s00330-002-1350-1|pmid=12271399|s2cid=16677678}}

Direct conversion imagers utilize photoconductors, such as amorphous selenium (a-Se), to capture and convert incident x-ray photons directly into electric charge.[http://www.agfa.com/en/he/knowledge_training/technology/direct_indirect_conversion/index.jsp Direct vs. Indirect Conversion] {{webarchive |url=https://web.archive.org/web/20100102204258/http://www.agfa.com/en/he/knowledge_training/technology/direct_indirect_conversion/index.jsp |date=January 2, 2010 }} X-ray photons incident upon a layer of a-Se generate electron-hole pairs via the internal photoelectric effect. A bias voltage applied to the depth of the selenium layer draw the electrons and holes to corresponding electrodes; the generated current is thus proportional to the intensity of the irradiation. Signal is then read out using underlying readout electronics, typically by a thin-film transistor (TFT) array.{{cite journal | last1 = Zhao | first1 = W. | last2 = Rowlands | first2 = J.A. | year = 1995 | title = Digital radiology using active matrix readout of amorphous selenium: theoretical analysis of detective quantum efficiency | journal = Medical Physics | volume = 24 | issue = 12| pages = 1819–33 | doi = 10.1118/1.598097 | pmid = 9434965 }}{{cite journal|last1=Zhao|first1=Wei|last2=Hunt|first2=D.C.|last3=Tanioka|first3=Kenkichi|last4=Rowlands|first4=J.A.|title=Amorphous selenium flat panel detectors for medical applications|journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment|date=September 2005|volume=549|issue=1–3|pages=205–209|doi=10.1016/j.nima.2005.04.053|bibcode=2005NIMPA.549..205Z }}

By eliminating the optical conversion step inherent to indirect conversion detectors, lateral spread of optical photons is eliminated, thus reducing blur in the resulting signal profile in direct conversion detectors. Coupled with the small pixel sizes achievable with TFT technology, a-Se direct conversion detectors can thus provide high spatial resolution. This high spatial resolution, coupled with a-Se's relative high quantum detection efficiency for low energy photons (< 30 keV), motivate the use of this detector configuration for mammography, in which high resolution is desirable to identify microcalcifications.M.J. Yaffe, “Detectors for Digital Mammography,” in Digital Mammography, edited by U. Bick and F. Diekmann (2010).

File:Flat panel detector.jpg]]

Flat-panel detectors are more sensitive and faster than film. Their sensitivity allows a lower dose of radiation for a given picture quality than film. For fluoroscopy, they are lighter, far more durable, smaller in volume, more accurate, and have much less image distortion than x-ray image intensifiers and can also be produced with larger areas.{{cite journal|last1=Seibert|first1=J. Anthony|title=Flat-panel detectors: how much better are they?|journal=Pediatric Radiology|date=22 July 2006|volume=36|issue=S2|pages=173–181|doi=10.1007/s00247-006-0208-0|pmc=2663651|pmid=16862412}} Disadvantages compared to IIs can include defective image elements, higher costs and lower spatial resolution.{{cite journal|last1=Nickoloff|first1=Edward Lee|title=AAPM/RSNA Physics Tutorial for Residents: Physics of Flat-Panel Fluoroscopy Systems|journal=RadioGraphics|date=March 2011|volume=31|issue=2|pages=591–602|doi=10.1148/rg.312105185|pmid=21415199|doi-access=free}}

In general radiography, there are time and cost savings to be made over computed radiography and (especially) film systems.{{cite journal|last1=Andriole|first1=Katherine P.|title=Productivity and Cost Assessment of Computed Radiography, Digital Radiography, and Screen-Film for Outpatient Chest Examinations|journal=Journal of Digital Imaging|date=1 September 2002|volume=15|issue=3|pages=161–169|doi=10.1007/s10278-002-0026-3|pmc=3613258|pmid=12532253}}{{cite web|title=CR versus DR -- what are the options?|url=http://www.auntminnie.com/index.aspx?sec=ser&sub=def&pag=dis&ItemID=58851|website=AuntMinnie.com|access-date=23 July 2017|date=31 July 2003}} In the United States, digital radiography is on course to surpass use of computed radiography and film.{{cite web|title=Medicare to cut analog x-ray payments starting in 2017|url=http://www.auntminnie.com/index.aspx?sec=ser&sub=def&pag=dis&ItemID=113334|website=AuntMinnie.com| date=7 February 2016 |access-date=23 July 2017}}{{cite web|title=Digital Radiology: Global Transition of the X-ray Image Capture Process|url=https://www.itnonline.com/article/digital-radiology-global-transition-x-ray-image-capture-process|website=Imaging Technology News|access-date=23 July 2017|language=en|date=8 February 2013}}

In mammography, direct conversion FPDs have been shown to outperform film and indirect technologies in terms of resolution{{reference needed|date=May 2020}}, signal-to-noise ratio, and quantum efficiency.{{cite book|last1=Markey|first1=Mia K.|title=Physics of Mammographic Imaging|date=2012|publisher=Taylor & Francis|isbn=9781439875469|page=9|url=https://books.google.com/books?id=P1XNBQAAQBAJ&pg=PA9|language=en}} Digital mammography is commonly recommended as the minimum standard for breast screening programmes.{{cite book|last1=NHS Breast Screening Programme|title=Clinical guidelines for breast cancer screening assessment|date=2016|publisher=Public Health England|edition=4|url=https://www.gov.uk/government/publications/breast-screening-clinical-guidelines-for-screening-management|language=en}}{{cite journal|last1=Lee|first1=Carol H.|last2=Dershaw|first2=D. David|last3=Kopans|first3=Daniel|last4=Evans|first4=Phil|last5=Monsees|first5=Barbara|last6=Monticciolo|first6=Debra|last7=Brenner|first7=R. James|last8=Bassett|first8=Lawrence|last9=Berg|first9=Wendie|last10=Feig|first10=Stephen|last11=Hendrick|first11=Edward|last12=Mendelson|first12=Ellen|last13=D'Orsi|first13=Carl|last14=Sickles|first14=Edward|last15=Burhenne|first15=Linda Warren|title=Breast Cancer Screening With Imaging: Recommendations From the Society of Breast Imaging and the ACR on the Use of Mammography, Breast MRI, Breast Ultrasound, and Other Technologies for the Detection of Clinically Occult Breast Cancer|journal=Journal of the American College of Radiology|date=January 2010|volume=7|issue=1|pages=18–27|doi=10.1016/j.jacr.2009.09.022|pmid=20129267|s2cid=31652981 }}

• X-ray detectors

{{Reflist}}

• [https://www.youtube.com/watch?v=_EQsPmT9F-8 Xray fluoroscopy with portable X-ray generator]

{{Medical imaging}}

Category:Nondestructive testing

Category:Radiography

Category:Medical imaging