RT12

• CR/DR stands for Computed Radiography/Digital Radiography
• CR/DR is filmless and involves reading from monitors
• CR/DR utilizes the use of PACS (Picture Archiving and Communication System)
• A digital image is an image that is stored on a computer and has been digitized
• Digital Image-This means that an image has been converted into various numbers that a computer can understand
• Each pixel in a digital image contains its own numerical value
• Spatial resolution refers to the ability to differentiate two objects and appreciate their differences
• Low spatial resolution makes it difficult to differentiate between objects that are close together
• Spatial resolution can be measured by spatial frequency, using line pairs per millimeter
• When lines on a phantom begin to blur together, it indicates low spatial resolution
• A matrix is a set of numbers displayed in a tabular form, arranged in rows and columns
• A digital image is an array of pixels, with each pixel containing a numerical value
• Contrast resolution is the ability to distinguish many shades of gray from black to white
• Digital imaging systems have better contrast resolution than screen-film imaging
• Bit is the fundamental unit of computer storage, representing a value of 0 or 1
• Pixel bit depth is the number of bits available to represent each pixel in the image
• Dynamic range is the number of gray shades an imaging system can reproduce
• It is the ability to distinguish structures with similar subject contrast
• DQE reflects the efficiency of photon detection and the noise added
• DR has a DQE of approximately 65%, while CR and film-screen have around 30%
• Two types of flat panels are Indirect Flat Panels and Direct Flat Panels
• Indirect Flat Panels consist of capture, coupling, and collection elements
• Direct Flat Panels have only capture and collection elements
• Advantages of DR over CR include immediate image display, faster processing, and slightly better resolution
• Disadvantages of DR over CR are higher cost, need for X-ray room refurbishment, and less flexibility
• Similarities between screen film imaging and CR imaging:

  • Both use an x-ray-sensitive plate encased in a protective cassette as the image receptor
• In screen-film radiography, the radiographic intensifying screen is a scintillator that emits light in response to an x-ray interaction
• In CR, the response to x-ray interaction is seen as trapped electrons in a higher energy metastable state
• Photostimulable luminescence (PSL):

  • Materials like barium fluorohalide with europium emit light promptly after x-ray exposure and later when exposed to a different light source
  • The activator is similar to the sensitivity center of a film emulsion
  • Barium fluorobromide atoms have atomic numbers of 56, 9, and 35 with Kshell electron binding energies of 37, 5, and 12 keV respectively
  • Compton and photoelectric x-ray interactions occur with outer-shell electrons, sending them into an excited, metastable state
• • Metastable electrons return to the ground state over time but can be accelerated or stimulated by exposing the phosphor to intense infrared light
• CR Cassette:

  • Looks like a conventional Radiography cassette
  • Made of durable lightweight plastic material backed by a thin sheet of Aluminum that absorbs x-rays
  • Contains an antistatic material instead of an intensifying screen to protect against static electricity build-up damage to the plate
• Layers of the Imaging Plate:

  • Protective layer: thin, tough, clear plastic that protects the phosphor layer
  • Phosphor/Active layer: traps electrons during exposure, usually made of phosphors from the barium fluorohalide family
  • Reflective layer: sends light in a forward direction when released in the cassette reader
  • Conductive layer: absorbs and reduces static electricity
  • Color layer: absorbs stimulating light but reflects emitted light
  • Support layer: semi-rigid material that gives strength to the imaging sheet
  • Backing layer: soft polymer that protects the back of the cassette
• Doping Barium Flurohallide with Europium:

  • Doping with Europium creates tiny defects called metastable sites of F center that trap electrons
• PhotoMultiplier Tube:

  • Laser beam stimulates the PSP plate, emitting visible light directed onto a photocathode layer
  • Electrons emitted from the photocathode are amplified through dynode plates
• Digitizing the signal:

  • Assigning numerical values to each light photon
  • Each phosphor storage is scanned and converted into a square matrix
  • More pixels result in greater resolution
  • Grey level determined by the number of photons detected, impacting image quality
• Erasing:

  • System automatically erases the plate by flooding it with light to remove any trapped electrons after initial reading
• Spatial Resolution:

  • Amount of detail in an image, determined by phosphor layer thickness and pixel size
  • Film Screen Radiography has 10 lp/mm, while CR has 2.5-5 lp/mm
• Speed:

  • CR system "speeds" reflect the amount of PSL emitted by the imaging plate during scanning
  • Different cassettes may have varying speeds, with special extremity or chest cassettes offering greater resolution
• Advantages of CR:

  • Improved diagnostic capabilities and reduced X-ray dosage
  • Reduced repeat rates and expanded diagnostic scope
  • Teleradiographic transmission and Picture Archival and Communication System (PACS) capabilities
• Recent Developments in CR:

  • Dual-sided reading and new line scan readers for improved signal-to-noise ratio and processing speed
  • Use of solid-state semiconductor laser diodes for reliability and consistency