Beam And Scatter Radiation Restricting Devices

DMI 50B Kyle Thornton

Scatter Radiation

Compton interaction Higher kVp energies in diagnostic range

As scatter increases, radiographs lose contrast

Radiographs will look dull, blurred, and fogged

Factors Affecting Scatter Radiation

kVp Field size Patient or part thickness

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

Beam Field Size

As field size is increased, scatter radiation increases

Restriction of field size improves image quality

Even more important during fluoroscopy

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

Compression Used to Decrease Effects of Scatter Radiation

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

Different Types of Beam Limitation Devices

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

Extension Cones And Cylinders

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

Cones and Cylinders

Comparison of Sinuses W/W-Out Use of Cones

Variable-Aperture Collimator

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

Automatically collimates to the size of film used

Does not relieve technologist of having to collimate to anatomy of interest