Projection Radiography

• Projection Radiography

  ● any static medical image
• Source of projection radiography:

  • X-rays
  • ionizing radiation
  • part of the electromagnetic spectrum emitted as a result of bombardment of a tungsten anode by free electrons from a cathode.
• Detector: materials that will receive the remnant radiation
• In conventional radiography we either use cassette (film) or imaging plate (filmless) as detectors
• Analog Detector (AKA Cassette): fluorescent screen and radiographic film
• Digital Detector (AKA Imaging plate): either digital or computed radiography
• computed radiography (CR) uses a photostimulable or storage phosphor imaging plate
• Direct Digital Radiography devices: convert X-ray energy to electron–hole pairs in an amorphous selenium photoconductor, which are read out by a thin-film transistor (TFT) array of amorphous silicon (Am-Si)
• Indirect DR Devices: light is generated using an X-ray sensitive phosphor and converted to a proportional charge in a photodiode (e.g., cesium iodide scintillator) and read out by a charge-coupled device (CCD) or flat panel Am-Si TFT array.
• Capture element: converts x-rays to light/electron
• Coupling element: transfers x-ray generated signals (e-) to the collection element; where processor starts
• Collection element:

  • stores e-/light
  • converts light to electrical signal
  • sends electrical signal to ADC (analog digital converter)
  • then from ADC ⇢ computer ⇢ process ⇢ DAC
• Indirect conversion:

  • x-ray ⇢ light ⇢ electrical signal
  • CR, Indirect DR
• Direct conversion:

  • x-ray ⇢ electrical signal
  • SPR, Direct DR
  • no coupling element
• Barium fluorohalide and photostimulable phosphor are doped with europium (activator)
• capture element of CR: barium fluorohalide and photostimulable phosphor
• coupling element of CR: Lens/Fiber optics
• collecting element of CR: Photodetector
• capture element of SPR: sodium iodide/cesium iodide
• coupling element of SPR: none
• collecting element of SPR: photodetector
• capture element of indirect DR with fiber optics as coupling element: cesium iodide
• coupling element of indirect DR with cesium iodide only as capture element: fiber optics
• collecting element of indirect DR with cesium iodide only as its capture element: Charge-coupled device/Complementary metal oxide semiconductor
• capture element of indirect DR with contact layer as its coupling element: cesium iodide, gadolinium oxysulfide
• coupling element of indirect DR with TFT as its collecting element: contact layer
• collecting element of indirect DR with contact layer as its coupling element: thin film transistor
• capture element of direct DR: amorphous selenium
• coupling element of direct DR: none
• collecting element of direct DR: Thin-film transistor
• • CCD: used for conventional radiography
  • CMOS: used for dental radiography
• image attributes in projection radiography includes variations in the gray scale of the image represent the X-ray attenuation or density of tissues
• BONE: absorbs large amounts of radiation allowing less signal to reach the detector, resulting in white or bright areas of the image
• AIR: has the least attenuation causing maximum signal to reach the detector, resulting in black or dark areas of the image
• projectional radiography is fast and easy to perform
• equipment in projectional radiography is relatively inexpensive and widely available; low amounts of radiation
• projectional radiography has high spatial resolution capability (no need for negatoscope). Particularly useful for assessing the parts of the body that have inherently high contrast resolution but require fine detail such as for imaging the chest or skeletal system
• projectional radiography has poor differentiation of low contrast objects
• superposition of structures in projectional radiography makes image interpretation difficult
• projectional radiography uses ionizing radiation (higher dose than screen-film)