DIGITAL RADIOGRAPHY

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DIGITAL RADIOGRAPHY
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Digital Fluoroscopy

• Input phosphor?output phosphor ?electronic signal
  ?beam splitter ?video signal ? TV monitor
• Video signal is a voltage signal which varies
  continuously ????
• ADC (Analog Digital Converter) converts analog
  to digital

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What are some negatives of conventional (film)
radiography?

• Difficult to image both soft tissue and bony
  structures in same image
• Difficult to differentiate between the subtle
  differences of soft tissues (shades of
  gray---long contrast, low contrast)
• Unable to gather quantitative info about
  attenuation characteristics of anatomy
• Image is processed permanent as is
• Amount of time needed to process
• Archiving/storage/ acquisition issues

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Similarities between CR and film radiography

• Same x-ray tube and generator
• Still select optimum kVp and mAs
• Accurate positioning
• Use cassette or image receptor
• There is still a latent image which can be
  processed into a manifest image

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DIFFERENCES

• Imaging plate rather than intensifying
  screen/film
• Photostimulable phosphor-europium activated
  barium fluorohalide phosphor
• 200 screen speed equivalent
• Phosphors absorb photons
• Capable of wider latitudes better visualization
  of soft tissues and bone

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DIFFERENCES CONT.

• Film made of minute strands of black metallic
  silver
• Digital image rows and columns called a matrix

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MATRIX, PIXEL AND VOXEL

• Matrix made up of pixels ( picture element)
• Pixels x-ray intensity at that location and
  given a numeric value for the shade of gray
• Voxel represent the volume of tissue of the
  patient
• Matrix preferred size 2048 x2048 or
• 4, 194,304 pixels
• Larger matrix more pixels and pixels are smaller

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IMAGE ACQUISITION

• Exit(remnant radiation) ?IP ?photons absorbed
  photoelectrically by phosphor ?LATENT IMAGE
• Exposed IP ?reader unit (digitizer) ?scanned to
  release energy as light ? photomultiplier tube
  (PMT) collects, amplifies and converts light to
  electronic signal ?to ADC ?manifest image

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• Manifest image is a matrix composed of pixels
  with assigned brightness levels
• IP scanned again with intense light to erase
  plate
• 10,000 readings

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Histograms/window or index levels/algorithms

• Histogram-graphic display of digital data
• Used to evaluate adequacy of IP to x-rays
• PMT needs to be adjusted to compensate for errors
• Window/index levels
• Algorithms math formulas needed to formulate
  image construction based on anatomy imaged
• Radiographer must indicate correct procedure so
  the correct algorithms are used.

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IP or IR
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IR/IP

• List some characteristics of an IP
• What speed film screen system is associated with
  a typical IP?
• How does this affect technique?

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DR

• DIRECT READOUT DIGITAL RADIOGRAPHY
• FLAT PANEL DIRECT CAPTURE DETECTOR
• CHARACTERISTICS?
• COMPARE INDIRECT CONVERSION TO DIRECT

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Post processing

• Subtraction
• Contrast enhancement
• Edge enhancement
• Black and white reversal
• Compensate for errors

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Misc.

• Resolution 2.5 line pairs per millimeter
• Window level adjusts image brightness
• Window width adjusts radiographic contrast
• Quantum mottle
• Artifacts
• Scatter

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• PACS
• HIS
• RIS