Beam And Scatter Radiation
Restricting Devices
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DMI 50B
Kyle Thornton
Scatter Radiation
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Compton interaction
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Higher kVp energies in diagnostic range
As scatter increases, radiographs lose
contrast
Radiographs will look dull, blurred, and
fogged
Factors Affecting Scatter
Radiation
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kVp
Field size
Patient or part thickness
kVp
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Compton interaction increases with
increasing kVp
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Scatter radiation increases
Scatter radiation is reduced by using
collimators and grids
Decreasing kVp is not always desirable
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Increases patient dose
Beam Field Size
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As field size is increased, scatter radiation
increases
Restriction of field size improves image
quality
Even more important during fluoroscopy
Patient Or Part Thickness
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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
Compression Used to
Decrease Effects of Scatter
Radiation
Beam-Restricting Devices
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Two types of devices to reduce scatter
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Restricted for two reasons
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Beam restricting devices
Grids
Reduce patient dose
Improve image contrast
Three types of beam-restricting devices
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Aperture diaphragm
Extension cones and cylinders
Variable aperture collimator
Positive beam limitation
Different Types of Beam
Limitation Devices
Aperture Diaphragm
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Simplest of all beam-restricting devices
Lead or lead-lined plate with an opening
Used with older head units
Cannot see a light
Extension Cones And
Cylinders
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Modifications of aperture diaphragms
Primarily used for headwork, L5-S1
Fixed openings
Generally not light localizing
Cones and Cylinders
Comparison of Sinuses W/WOut Use of Cones
Variable-Aperture Collimator
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Light localizing
Most commonly used
A series of shutters and mirrors used
Light field must coincide with x-ray beam
Variable Aperture Device
Schematic Drawing of the
Variable Aperture Device
Positive Beam Limitation
Devices
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Automatically collimates to the size of film
used
Does not relieve technologist of having to
collimate to anatomy of interest