Flat panel detector

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A portable @Si flat panel detector is used to visualise the movement of liquids in sand cores under high pressure.

Flat panel detectors are a class of solid-state x-ray digital radiography devices similar in principle to the image sensors used in digital photography and video. They are used in both projectional radiography and as an alternative to x-ray image intensifiers (IIs) in fluoroscopy equipment.


X-rays pass through the subject being imaged and strike one of two types of detectors.[1]

Indirect detectors[edit]

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.[2] 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.[3]

Direct FPDs[edit]

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. The charge pattern is then read by a TFT array in the same way images produced by indirect detectors are read.[4]


Flat panel detector used in digital radiography

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. They are lighter, far more durable, smaller in volume, more accurate, and have much less image distortion than image intensification detectors and can also be produced with larger areas.[5] Disadvantages compared to IIs can include defective image elements, higher costs and lower spatial resolution.[6]

See also[edit]


  1. ^ Goel, Ayush. "Flat panel detectors". Radiopaedia.org. Retrieved 12 September 2014. 
  2. ^ Kump, K; Grantors, P; Pla, F; Gobert, P (December 1998). "Digital X-ray detector technology". RBM-News. 20 (9): 221–226. doi:10.1016/S0222-0776(99)80006-6. 
  3. ^ Kotter, E.; Langer, M. (19 March 2002). "Digital radiography with large-area flat-panel detectors". European Radiology. 12 (10): 2562–2570. doi:10.1007/s00330-002-1350-1. 
  4. ^ Zhao, Wei; Hunt, D.C.; Tanioka, Kenkichi; Rowlands, J.A. (September 2005). "Amorphous selenium flat panel detectors for medical applications". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 549 (1-3): 205–209. doi:10.1016/j.nima.2005.04.053. 
  5. ^ Seibert, J. Anthony (22 July 2006). "Flat-panel detectors: how much better are they?". Pediatric Radiology. 36 (S2): 173–181. doi:10.1007/s00247-006-0208-0. PMC 2663651Freely accessible. 
  6. ^ Nickoloff, Edward Lee (March 2011). "AAPM/RSNA Physics Tutorial for Residents: Physics of Flat-Panel Fluoroscopy Systems". RadioGraphics. 31 (2): 591–602. doi:10.1148/rg.312105185Freely accessible. 

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