Filtration (VOCAB)

Added filtration

Any filtration that occurs outside of the X ray tube and housing

Al/eq

Aluminium equivalent- the absorption property of a material is expressed as how well the material absorbs x ray photons as compared to how well aluminum absorbs x ray photons

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 the unequal body part thickness.

E.g. thoracic spine where the body is thinner near the neck than in the abdomen

Compound Filter

Used 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 the 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

The amount of absorbing material that will reduce beam intensity to half its original amount. Code of Federal regualtion’s establishes requirements’s for equipment HVL

Inherent filtration

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

Thoraeus Filter

Compound filter used in radiation therapy which combines tin, copper, and aluminium, in that order

Total Filtration

The sum of inherent and added filtration of the tube. (Does not include compound or compensating filters) National council on radiation protection requires that equipment operating above 70 KVP must have a minimum filtration of 2.5mm Al/eq

Trough Filter

Compensating filter most commonly used to visualize structures of the media strum without overexposing the lungs

Wedge Filter

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

e.g Thoracic spine, thigh, foot, etc

• % attenuation achieved by specific amounts of filtration at various KV levels found on page 153 of Carlton Alder text

• Filtration greater than 3mm is typically not used because the reduction to entrance skin dose does not warrant the tube loading increase (Beneficial effect is diminished)