Filtration Vocabulary

Added Filtration

any filtration that occurs outside of the x ray tube and housing

Al/eq

aluminum equivalent, the absorption property of a material is expressed as how well the material absorbs xray photons as compared to how well aluminum absorbs xray

Collimator

the mirror of the collimator provides approximately 1 mm Al/eq filtration

Compensating Filter

an absorber that compensates for unequal absorption of the subject - used to even out unequal densities resulting from uneal body part thickness

Compound Filter

uses two or more materials that complement one another in their absorbing abilities. Each layer absorbs the characteristic photons created by the previous layer

Filter

any material designed to effectively absorb photons from x-ray beam (purpose is to reduce low energies and reduce patient dose)

Filtration

the process of eliminating undesirable low energy x-ray photons by inserting an absorbing material into the primary beam

Half-Value Layer

that amount of absorbing material that will reduce beam intensity to half its original amount. Code of federal regulations establishes requirements for equipment HVL

Inherent Filtration

filtration as a result of composition of the tube and housing - typically amounts to 0.5 to 1.0 mm of Al/eq with most coming from the tube window itself

Thoraeus Filter

compound filter used in radiation therapy which combines tin, copper and aluminum, in that order

Total Filtration

the sum of inherent and added filtration of the tube. (Does not include compound compensating filters).

National council of radiation protection requires that equipment operating above 70 kVp must have a minimum filtration of 2.5 mm Al/eq

Trough Filter

compensating filter most commonly used to visualize structures of the mediastinum without overexposing the lungs

Wedge Filter

compensating filter shaped in a wedge, used to compensate for unequal thickness of the anatomy of interest