Rad Tech 265

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Rad Tech 265

• More Digital Imaging

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Digital Fluoroscopy

• Radiation dose
• Patient dose for DF is significantly less than
  conventional fluoro
• At 7.5 pulses/second DF has a 75 drop in
  exposure
• At 3 pulses/sec a 90 reduction in dose
• The lower dose is obviously advantageous for
  pediatric work.

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Types of DF

• The most common methodology is to add a CCD to
  the video chain.
• A truly digital system can be either indirect or
  direct.
• Pulse progressive fluoroscopy
• Uses a high frequency generator with regular mA
  values

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Digital Fluoroscopy Room
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Flat panel vs. Image Intensifier
Flat panel
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Field coverage / size advantage to flat panel
Image distortion advantage to flat panel
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Flat vs. Fat
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Direct DF

• In direct capture or direct to digital systems,
  x-ray energy is not converted to light. Instead,
  it is captured by a thin film transistor matrix
  of a material such as amorphous selenium that
  changes it into electronic signals. No
  intensifying screen is required, and none of the
  energy is lost through scatter, as happens when
  x-ray energy is converted to light on its way to
  display of an image.

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Indirect DF

• The indirect capture systems, including some flat
  panel displays that can be integrated into analog
  systems, are similar conceptually to the
  traditional film-screen technology. In one
  version, a cesium iodide scintillator captures
  the x-rays as they exit the patient and converts
  them to light. This light is turned into
  electronic signals by a matrix of amorphous
  silicon sensors. Each sensor corresponds to a
  single pixel of the image and is connected to a
  readout line. The signals from each cell in the
  matrix are read out in sequence row by row to
  obtain the image. High information transfer rates
  permit the display of moving images.

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Indirect v. Direct

• Notice, that the comparison of direct v. indirect
  digital fluoroscopy is the same as direct v.
  indirect digital radiography.
• In the indirect systems, the photons are
  converted to a light image first before being
  digitized.

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Direct v. Indirect
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Direct v. Indirect Resolution
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Digital v Conventional Film
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Digital v. Analog
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Acquisition steps
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Image Manipulation with DF

• Pan/zoom, background noise reduction, adjustable
  contrast and brightness, edge enhancement,
  quantitative analysis of vessel diameter and
  stenosis severity, subtraction capabilities,
  roadmapping, and bolus chase are common.

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Pixels (matrix)
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Matrix size
32 x 32
128 x 128
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Matrix size
128 x 128
512 x 512
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Edge enhancement
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Bits (gray scale)
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Bits
4 bits
8 bits
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Temporal averaging
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Last image hold (lih)
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DSA
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DSA
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DSA
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Digital Tomosynthesis reduce structured noise

• 3 cm above detector
• 9 views, to - 30
• 1.4 x dose

Tomographic ramp
Niklason, L.T. et.al. Radiology 205399-406