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Take 7: Image Intensifier vs Flat Panel Detector

As mentioned before in "Take 4," the Image Intensifier (II) and Flat Panel Detector (FPD) are important fluoroscopic components that function similarly yet are different.  Since we know that the purpose of each component is to brighten the image without increasing dose, here is a brief comparison of the difference of both the II and FPD.

Here is what's different about the II:
  • Consists of input phosphor, photocathode, electrostatic focusing lenses, anode, output phosphor, and glass envelope
    • Input phosphor: absorb and convert x-rays to light photons
    • Photocathode: absorbs the light created by input phosphor and then emits photo(light)electrons
    • Electrostatic focusing lenses: guides and directs photoelectrons to output phosphor
    • Anode: these photoelectrons then pass through the anode
    • Output Phosphor: converts the photoelectrons that exited the anode to light photons


Here is what's different about the FPD:
  • "All flat panel detectors used in radiology convert a flux of x-rays into an electrical charge.  This electrical charge is digitized in the detector's readout matrix" (ASRT, 2010).
    • Composed of amorphous silicon thin- film transistor (TFT)
    • TFT is an arrangement of rows and columns
      • Rows: formed by gate lines that operate the TFT (ASRT, 2010)
      • Columns: linked by drain lines that are connected to the TFT output (ASRT, 2010)
      • Drain lines: connect to charge amplifiers
      • Charge amplifiers: receive the charge from detector elements
  • Two different methods to convert x-rays to electrical charge:
    • Indirect Conversion
      • A phosphor (scintillator)interacts with incoming x-rays to produce light photons
      • A photoconductor such as a Charge-Coupled Device (CCD)then converts light to electrical charge
    • Direct Conversion
      • "An x-ray photoconductor directly converts the x-ray photons into an electrical charge" (ASRT, 2010).



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