Beam And Scatter Radiation Restricting Devices

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Beam And Scatter Radiation Restricting Devices

• DMI 50B
• Kyle Thornton

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Scatter Radiation

• Compton interaction
• Higher kVp energies in diagnostic range
• As scatter increases, radiographs lose contrast
• Radiographs will look dull, blurred, and fogged

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Factors Affecting Scatter Radiation

• kVp
• Field size
• Patient or part thickness

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kVp

• Compton interaction increases with increasing kVp
• Scatter radiation increases
• Scatter radiation is reduced by using collimators
  and grids
• Decreasing kVp is not always desirable
• Increases patient dose

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Beam Field Size

• As field size is increased, scatter radiation
  increases
• Restriction of field size improves image quality
• Even more important during fluoroscopy

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Patient Or Part Thickness

• Scatter increases with patient or part thickness
• A chest x-ray will result in more scatter than an
  arm x-ray
• Compression devices reduce patient thickness and
  improve quality

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Beam-Restricting Devices

• Two types of devices to reduce scatter
• Beam restricting devices
• Grids
• Restricted for two reasons
• Reduce patient dose
• Improve image contrast
• Three types of beam-restricting devices
• Aperture diaphragm
• Extension cones and cylinders
• Variable aperture collimator
• Positive beam limitation

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Aperture Diaphragm

• Simplest of all beam-restricting devices
• Lead or lead-lined plate with an opening
• Used with older head units
• Cannot see a light

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Extension Cones And Cylinders

• Modifications of aperture diaphragms
• Primarily used for headwork, L5-S1
• Fixed openings
• Generally not light localizing

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Variable-Aperture Collimator

• Light localizing
• Most commonly used
• A series of shutters and mirrors used
• Light field must coincide with x-ray beam

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Positive Beam Limitation Devices

• Automatically collimates to the size of film used
• Does not relieve of technologist of having to
  collimate to anatomy

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Collimator Filtration

• Some collimator housing units come with
  interchangeable filtration
• Generally, different millimeter thicknesses of
  aluminum is used