ch.11 filtration

Filtration

The process of eliminating undesirable low-energy X-ray photons by insertion of absorbing materials into the primary beam, with the primary purpose of lowering patient dose

Inherent filtration

Any material that filters X-rays that must be present for the tube to work including the glass envelope, dielectric oil bath, and glass window of housing

Added filtration

Any filtration outside the tube housing and before the image receptor that the tube can operate without, such as the collimator and aluminum sheets

Half-value layer

The thickness of material needed to reduce an X-ray beam to half of its original intensity used in quality control to measure total X-ray beam quality

Total filtration

The sum of inherent filtration plus added filtration, which, most be at least 2.5mm aluminum equivalent for machines operating above 70 kVp

Beam hardening

The process of increasing the average energy of the X-ray beam by removing low-energy soft photons through filtration

Compound filtration

Filtration using two or more materials with different k-edge properties, typically copper and aluminum where each layer absorbs characteristic photons created in the previous layer

Compensating filtration

Filters designed to even radiographic density with parts that have uneven tissue thickness or densities, such as wedge fifers for feet or t-spine

Photoelectric effect

The interaction where low-energy photons are completely absorbed by tissue contributing to patient dose without adding diagnostic value to the image

Aluminum equivalency

The standard measurement unit for expressing filtration, based on the thickness of aluminum that would provide equivalent filtering effect

K-edge

The property of a filter material where its k-shell binding energy is close to the strength of the photons it's designed to absorb 'ensuring photoelectric interaction and effective filtration

Soft photons

Low-energy X-ray photons with longer wavelengths and lower frequencies that cannot penetrate tissue effectively and only contribute to patient dose without diagnostic value

Hard photons

High-energy X-ray photons with shorter wavelengths and higher frequencies that have greater penetrating power and contribute to the diagnostic image

Sunburning

The natural increase in inherent fitration that occurs as an X-ray tube ages due to tungsten deposits from vaporization forming on the inside of the tube

Copper filtration

A type of added filtration gaining popularity that can reduce entrance surface exposure by 25%.44% when coupled with aluminum to take advantage of the k-edge properties of both materials

30-40 keV

Soft tissue penetration threshold

Effect of filtration on image contrast

Makes the scale of contrast longer by removing low - energy photons resulting in a more uniform and homogeneous primary beam that produces more consistent image qualify

Effect of filtration on intensity

Decreases the number of photons (intensity) in the primary beam while increasing the average strength of remaining photons

Effect of filtration on penetrability

Increases the average penetrating power of the xray beam by removing low-energy photons and allowing higher-energy photons to pass through

Mirror in collimator

Considered inherent filtration due to the silver backing, which cannot be removed

Grids vs. Filters

Grids are not considered filters because they are positioned behind the patient and serve to clean up scatter radiation rather than harden the primary beam

Direct

KVP and half-value layer have a — ______ relationship because higher energy beams require more material to be reduced by half

Characteristic Cascade X-rays

Secondary radiation produced when electrons fall into vacated Shells during the X-ray production process, which filtration helps eliminate

Relationship between filtration and photoelectric effect

Filtration reduces photoelectric interactions in the patient by removing low- energy photons that would otherwise be completely absorbed by tissue