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					Digital Radiography
    DMI 50B
    Kyle Thornton
What Does That Mean?
 Digital has a higher dynamic range
  than film
 The response is linear v. sigmoidal
 It provides more information at the
  low and high exposure levels
Digital v. Computed v.
Direct Capture Radiography
   Computed Radiography
       Uses a cassette with an imaging plate
   Digital Radiography
       Uses a linear array of radiation
        detectors
        • Similar to Computed Tomography
   Direct Capture
       Uses a solid-state radiation detector
        device
Computed Radiography
   A cassette is used
       Contains a photostimulable phosphor
        imaging plate
        • Looks like an intensifying screen
        • Contains a layer of europium-doped barium
          fluorohalide crystals
        • When struck with x-rays, a new semistable
          state is produced
        • The latent image is stored on this plate
The Imaging Plate
   Made up of multiple layers
       A polyester support layer
       The phosphor layer
       A clear protective layer
       Reflective layer
       Conductive layer
       Support layer
       Backing layer
       Bar code label on the bottom
         • Contains a number assigned to the image plate
The Imaging Plate
 Very flexible
 Can maintain a latent image for
  about 24 hours
     Can be exposed to light
     Some image degradation may occur
      with extended storage time and light
      exposure
The Image Reader
   Converts the analog information from the
    latent image to a digital format
   The image plate is scanned by laser
   The portion of the plate struck by laser
    emits light
   The light is directed to photomultiplier
    tubes that convert it to digital electric
    signals
   Most modern readers can process 110 –
    140 plates per hour
Terminology
   Rotation/inversion
       The ability to change the image presentation,
        or turn the image from a negative to positive
   Anatomic measurements
       The ability to measure certain areas of
        interest
   Short-term database functions
       Allows user to locate images, create lists of
        images, image interpretation, and maintain
        teaching files
More Terminology
   Gradation Processing
       Controls the range of densities used to display
        structures on the image
   Spatial Frequency
       Controls the sharpness of boundaries between
        two structures of different densities
   Dynamic Range Control
       Provides a wide diagnostic field
         • Allows for visualization of bone and soft tissue in a
           single image display
Even More Terminology
   Magnification
       Allows enlargement of a specific area to
        enhance viewing and diagnosis
   Subtraction
       Allows the user to enhance certain
        areas of interest while fading other
        areas from view
        • Enhancing from vascular detail while fading
          superimposing bony detail
Image Storage
 Magnetic tape and optical disk
 Each CR image contains app. 8
  megabytes of data
CR Image Characteristics
   Image resolution
     Dimension of the crystals in the
      imaging plate
     Size of the laser beam in the reader

     The image reading matrix
        • CR images average 2 – 5 lp/mm
        • Standard film demonstrates 3 – 6 lp/mm
Digital Radiography
   X-ray tubes for DR have a high heat
    capacity
       In excess of 1 MHU
   DR does not use cassettes
     A radiation detector array is used
     These detectors are gas-filled

     The more detectors, the better the
      spatial resolution
Direct Capture Radiography
   Image forming x-rays interact with
    cesium iodide phosphors
     Patient dose is less with this approach
     Or

   They interact with a thin layer of
    selenium
       There is no spreading of light and
        spatial resolution is improved
Digital Fluoroscopy
   A computer and two video monitors
    are required
     One video monitor is used to edit
      patient data
     One monitor displays the image

   The operating console is more
    complex
       Allows for the input of patient data
Digital Fluoroscopy
   The video monitor is often a 1000 line
    system as opposed to 525
   The video signal is read in a progressive
    mode
   The electron beam of the of the TV
    camera tube sweeps the target assembly
    continuously from top to bottom in 33
    ms.
   There is no interlace of fields
       The image is sharper with less flicker
Digital Fluoroscopy and
Dose
 Static images are made with a lower
  dose rate than with 105mm spot
  film cameras
 Most DF x-ray beams are pulsed
 The dose to the patient is about half
  that of conventional image
  intensified fluoroscopy
PACS
   Picture Archive and Communication
    System
     Allows for the digitization of
      conventional radiographs
     Allows for acquisition, interpretation,
      and storage of images
The Three Components of a
PACS
 Display System
 Network
 Storage System
Display System
   This is a cathode ray tube monitor
   Provides a workstation for the operator
   Must be very high resolution
       Ranges from 256 X 256 – 1024 X 1024
       This is lower than the spatial resolution of film
         • The operator is able to subtract, use edge
           enhancement, window-level, highlight, pan, scroll
           and zoom on the monitor
The Image Matrix
   A layout of cells in rows and columns
   Each cell is a specific location in the
    matrix
       Each cell is called a pixel
   Each digital image consists of a matrix of
    cells
       The matrix has various brightness levels
       The level of brightness depends upon the
        atomic number and mass density of the tissue
        that has received x-rays
Network
   A number of computers connected to one
    another
   In a PACS, many people have access to
    an image for different purposes
   Data from one unit to another is first
    digitized
   Images can be transferred to another
    workstation for interpretation
       This is known as teleradiology
Storage System
 PACS is able to archive
 Images are not lost
 The file room is replaced by a
  magnetic or optical memory device
 Electronically, images can be
  recalled to any workstation in
  seconds
Pitfalls and Acceptance of
CR and DR
   The acceptance of the system is increasing
      This is the future and in many imaging
       departments, the future is now!
   Department efficiency is increased
   It does not provide a traditional format
   Some resolution is lost
   Edge enhancement artifacts may actually create
    pathology
   Due to the increased latitude in image
    production, the patient may be exposed to too
    much radiation
CR – DR and Patient Dose
   If used correctly patient dose can be
    decreased
     CXR – 5% decrease
     UGI – 5% decrease

     IVP – 10% decrease

     Pediatric examinations – 15 – 30%
      decrease

				
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posted:9/23/2011
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