Radiographic Imaging Image Production

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Radiographic ImagingImage Production
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Terms Related to Image Production

• Primary Radiation
• Refers to the x-ray beam after it exits the x-ray
  tube and before it interacts with the patients
  body
• Remnant Radiation
• The remainder of radiation after it passes
  through the patients body.
• This is what produces the image on the
  radiographic film
• Secondary Scatter Radiation
• Radiation that may not be able to reach the film
  but does not carry any useful information

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Terms Related to Image Production

• Attenuation
• The process by which primary radiation is changed
  or absorbed as it travels through the patient
• Radiolucent
• Material that allow x-ray photons to pass through
  easily (air)
• Radiopaque
• Materials that do not allow x-ray photons to pass
  through easily (bone)

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Film / Screen RadiographyThe Imaging Chain

• Latent Image
• The image that is invisible on the radiographic
  film until processing occurs
• In order to release that image the film must be
  developed.

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Film / Screen RadiographyThe Imaging Chain

• Radiograph
• Image that is produced by x-ray photons on a
  piece of radiographic film

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Film / Screen RadiographyThe Imaging Chain

• Intensifying Screens
• Thin layers of cardboard or polyester coated with
  layers of luminescent phosphor crystals that are
  sensitive to x-rays.
• In order to take full advantage of
  intensification process, an intensifying screen
  was placed in the front and back of the x-ray
  film.

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Film / Screen RadiographyThe Imaging Chain

• Double or Duplized emulsion film
• A special film that utilizes two intensifying
  screens, one in the front and one in the back of
  the film to enhance the intensification process.

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Technical Exposure Factors

• Exposure Factors directly under the influence of
  the radiographer
• mAs
• kVp
• SID

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mAs

• Milliampere seconds
• Controls the amount of radiation coming from the
  x-ray tube and time the x-rays are being produced
• Controls the quantity or number of x-ray photons
  produced

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kVp

• Kilovoltage peak or potential
• Measures the potential difference forcing the
  current through the x-ray tube
• It affects the energy or quality or power of the
  x-ray photons

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SID

• Source to image distance
• The distance between the point of x-ray emission
  and the image receptor
• Also known as focal film distance (FFD) or target
  film distance (TFD)

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Factors Affecting Radiographic Quality

• Density
• The overall blackening of the film

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Variables That Affect Density

• Patient size and tissue composition
• The density of the tissues affect the visible
  density on the radiographic film
• The denser the tissue, the lighter the
  corresponding film
• mAs
• The chief controlling factor of exposure and
  density
• Increasing mA or time increases the radiographic
  density

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Variables That Affect Density

• kVp
• kVp affects density differently than mAs. In
  order for there to be a significant increase in
  density a 15 change in kVp must be made.
• There is a peak or optimal kVp for each body part
• Distance
• Distance is inversely related to density
• A decrease of distance of the source of x-rays to
  film increases the density and vice versa
• Known as the Inverse Square Law

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Factors Affecting Radiographic Quality

• Beam Modification
• Anything that changes the nature of the radiation
  beam.
• The beam may be modified before it enters the
  patient (primary beam modification) or before it
  interacts with the film (scatter control)

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Factors Affecting Beam Modification

• Filtration
• The use of attenuating or absorbing material
  between the x-ray tube and the patient that
  filters out non-diagnostic, low energy, x-ray
  photons.
• Half value layer
• The amount of attenuating material that it takes
  to reduce the primary x-ray beam to one half of
  its original value.
• Beam limitation devices
• Anything that will change the size of the primary
  x-ray beam

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Factors Affecting Radiographic Quality

• Grids
• A device that is designed to remove as many
  scattered photons exiting the patient as possible
  before they reach the film.
• Consist of thin lead strips interspersed with
  spacing material
• Placed between the patient and the film to
  intercept scattered photons leaving the patient.

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Factors Affecting Grids

• Grid Ratio
• The ratio of the height of the lead strips to the
  distance between them.
• Grid ratios range from 51 to 161
• The higher the grid ratio the less density that
  reaches the film

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Factors Affecting Radiographic Quality

• Film / screen combinations
• Intensifying screens are fluorescent screens that
  glow when exposed to x-radiation.. They are used
  to enhance the radiation so that fewer x-ray
  photons are used to create a radiographic image.
  
• The color of the glow of the intensifying screen
  must match the color sensitivity of the film
  (spectral matching)

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Factors Affecting Radiographic Quality

• Relative speed of the film screen system
• The speed of an x-ray film system range from 50
  to 1200.
• The faster the speed of the system, the greater
  the density on the radiographic film it creates
  and the fewer x-ray photons it takes to create an
  image.

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Factors Affecting Radiographic Quality

• Processing
• Chemicals used to process or develop the
  radiographic film may affect the density
• Most common change in density is temperature
• Temperature to hot, increases radiographic
  density
• Temperature to cold, decreases radiographic
  density

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Contrast

• The visible difference between adjacent
  radiographic densities.
• The black and white and all shades of gray of the
  x-ray film

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Factors Affecting Radiographic Quality

• Patient Factors
• Because tissues in the body attenuate x-rays
  differently, tissues with similar attenuation
  will have similar density as well as contrast.

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Factors Affecting Radiographic Contrast

• kVp
• The chief controlling factor of contrast
• The higher the kVp, the lower the contrast
• The lower the kVp, the higher the contrast

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Factors Affecting Radiographic Contrast

• mAs
• A secondary factor for contrast. No change in
  mAs can make up for inadequate penetration (kVp)

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Factors Affecting Radiographic Contrast

• Beam Modification
• Anything that decreases scatter, increases
  contrast.

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Factors Affecting Radiographic Contrast

• Film / screen combination
• Imaging systems are complementary to the body
  structures or areas of the body
• In theory, the faster the system, the higher the
  contrast

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Factors Affecting Radiographic Contrast

• Contrast media
• Substances that attenuates the beam to a
  different degree than the surrounding tissue
• Used to enhance areas of the body that have the
  same attenuation of surrounding tissue
• Contrast media increases contrast on film

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Factors Affecting Radiographic Contrast

• Processing
• Inadequate processing degrades the radiographic
  contrast

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Recorded Detail

• The distinct representation of an objects true
  borders or edges
• It is often called sharpness of detail,
  definition or resolution

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Factors Affecting Radiographic Recorded Detail

• Motion
• Voluntary motion
• Motion caused by the movement of the patient.
• Best controlled by good patient instructions
• Involuntary motion
• Motion caused by uncontrolled motion of the body
  such as the heart beat or peristalsis
• Best controlled by short exposure times

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Factors Affecting Radiographic Recorded Detail

• Object unsharpness
• The inherent unsharpness of an object due to its
  shape and location

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Factors Affecting Radiographic Recorded Detail

• Focal spot size
• A small focal spot is used when fine detail is
  needed
• A large focal spot is used all other times

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Factors Affecting Radiographic Recorded Detail

• Source to image distance (SID)
• As SID increases detail increase
• Penumbra
• A fuzzy border of an object that is obscure
• Umbra
• The true boarder

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Factors Affecting Radiographic Recorded Detail

• Object to Image Distance (OID)
• The smaller the OID, the better the recorded
  detail

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Factors Affecting Radiographic Recorded Detail

• Material Unsharpness
• Faster systems produce greater unsharpness of
  detail

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Factors Affecting Radiographic Recorded Detail

• Distortion
• The misrepresentation of the true size or shape
  of an object
• Most commonly known as magnification

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Types of Distortion

• Size distortion
• Magnification
• The best image is produced by the smallest OID
  and the largest SID
• Shape distortion
• The misrepresentation of the shape of a
  radiographic image
• Images in the direct path of the central ray are
  the most accurately represented

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THE END