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Chapt 28 The Digital Image

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Title: Chapt 28 The Digital Image Created Date: 3/30/2009 3:06:54 PM Document presentation format: On-screen Show (4:3) Company: UNLV Other titles – PowerPoint PPT presentation

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Title: Chapt 28 The Digital Image


1
Chapt 28 The Digital Image
  • Spatial resolution
  • Contrast resolution
  • Contrast-detail curve
  • Pt. Dose considerations

2
Spatial resolution
  • -the ability of an imaging system to RESOLVE and
    render on the image a HIGH CONTRAST object
    (shades of gray differences in close objects to
    one another)

3
Spatial FREQUENCY
  • Refers to LINE PAIR!
  • Line pair per millimeter )lp/mm)
  • The higher the spatial frequency, the HIGHER the
    spatial resolution!
  • In digital imaging, spatial resolution is limited
    by PIXEL size.

4
Modulation Transfer Function (MTF)
  • The ability of an imaging system to render
    objects of DIFFERENT sizes onto an image (ratio
    of image to object due to spatial resolution)

5
Contrast Resolution
  • The HIGHEST possible contrast is TWO shades of
    gray Black and White!

6
Dynamic Range
  • -is really the OD shown on the H D curve
    ranges from base fog (.2 or lower) to the
    solarization point
  • The number of shades of GRAY that an imaging
    system can produce (remember the human eye can
    only see about 30 different shades of gray!)

7
NOISE
  • Image noise limits contrast resolution (SNR)
  • Post processing of the image allows for
    manipulation and visualization of shades of gray
    (window and leveling)

8
Patient dose
  • Digital imaging should reduce pt. dose (in
    reality, it had done just the reverse!) the in
    in doubt, burn it out syndrome and post image
    manipulation dose creep!

9
Misc. information
  • Focal spot size determines spatial resolution in
    film/screen systems
  • Post image manipulation contrast resolution in
    digital regardless of pt. dose
  • Pt. dose in digital should be LOW because of DQE
    (probability of a photon interacting with an
    image receptor due to atomic number, etc)
  • DQU measure of x-ray absorption efficiency
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