Basic Concepts of Other Imaging Modalities

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Basic Concepts of Other Imaging Modalities

• Dent 5101

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Body-section Radiography

• A special radiographic technique that blurs out
  the shadows of superimposed structures
• Object of interest less blurred
• Does not improve the sharpness

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Tube and Film Move in Opposite Direction
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• Tube and film move in opposite direction, and
  rotate about a fulcrum
• The level of the fulcrum is the focal plain

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Blurring

• Determined by
• Distance of the tube travel
• Distance from the focal plain
• Distance from the film
• Orientation of tube travel

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Types of Tomographic Motions
Linear
Circular
Elliptical
Trispiral
Hypocycloidal
Figure 8
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Panoramic Radiography
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Panoramic Radiography

• Obtained by rotating a narrow beam of radiation
  in the horizontal plane
• The film is rotated in the opposite direction
  while the object (jaws) is stationary

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Focal Trough

• A 3-dimensional curved zone or image layer in
  which structures are reasonably well defined.

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Types of Panoramic Machines

• Panorex Two centers of rotation. Interruption
  of exposure in the midline
• Orthopantomogram Three centers of rotation.
  Continuous image

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Panorex Image
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Orthopantpmograph
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Image Intensification
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Early Fluoroscopy

• Early fluoroscopy done by direct observation
• Screen was poorly illuminated - image perception
  inadequate

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Image Intensification

• Image intensifier improved viewing of fluoroscopy

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Intensifier Tube

• Four parts
• Input phosphor and photocathode
• Electrostatic focusing lens
• Accelerating anode
• Output phosphor

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Intensifier Tube (Cont.)

• Input phosphor cesium iodide (CsI) or
  zinc-cadmium-sulfide.
• Photocathode A photo-emissive metal.
• Electrostatic focusing lens series of
  negatively charged electrodesfocuses the
  electron beam.
• Output phosphor Provides thousand-fold more
  light photons.

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Intensifier Tube

• Used in
• Sialography
• Arthrography

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Digital Imaging
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Digital Imaging

• Conventional film-intensifying screen radiograph
  - analog image.
• Digital radiographfilm-less.
• Conventional films can be digitized, with a
  likelihood of loss of information.

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Photostimulable Phosphor (PSP)

• Storage phosphor
• Indirect Digital Radiography
• Similar to the intensifying screen phosphors
• Difference - PSP traps a significant number of
  electrons in its phosphor, which is later read by
  a laser beam

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Photostimulable Phosphor (PSP)
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Charge-coupled Devices

• An amorphous silicon wafer containing an array of
  pixels (picture elements)
• Each pixel acts as a capacitor storing charge
• On radiation exposure, electric charge is
  deposited in the pixels proportional to the
  intensity of the beam
• The variation in charge deposition can be
  digitally converted to an image

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Pixels

• Each square (pixel) has its own color (numerical
  value)

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Pixel Array
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CMOS

• Complimentary Metal Oxide Semiconductor
• Principle similar to CCD
• Simpler circuit design

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CCD, CMOS
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Resolution

• Ability to identify two different objects that
  are close to each other
• D-speed films gt10 line pair/mm
• Digital images7-10 line pair/mm
• Eyes 4-6 line pair/mm

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Digital Subtraction

• Shows changes in an area over time
• Requires two films exposed with similar geometry
  

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Digital Subtraction

• Two radiographs are obtained
• Identical position
• One superimposed over another
• Differences in two images identified digitally
• Allows identifying changes in hard tissue that
  occurred between the two examinations

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Radiation Dose
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Image Processing/Reconstruction

• To improve diagnostic accuracy
• May improve the diagnosis of one disease, while
  obscure another
• Fraud

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Digital Radiography Advantages

• Instant images
• Consistent quality
• High signal/noise ratio
• Image Manipulation
• Lower radiation dose

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Disadvantages

• Lower resolution
• Quality depends on monitor and printer
• Print quality often not optimal
• Higher initial cost
• Unwanted manipulation of images