Exposures: chapter 11

filtration

the elimination of undesirable, low energy x-ray photons, by the insertion of absorbing materials into the beam

increase

if low energy x-ray photons were in the beam they would be absorbed by patient and ___ patient dose

decrease patient dose

purpose of filtration?

higher, less

During filtration, we have ___ average energy beam and ___ # of photons in the beam 

filtration

hardens the beam

soft photons

low-energy x-ray photons, which means hardening

filter

material that is designed to selectively absorb x-ray photons

aluminum

what is the standard filtering material?

millimeters (mm Al/Eq)

all filtration is expressed in ___ of aluminum equivalency

half value layer

what does HVL stand for?

HVL

the amount of absorbing material that will reduce the intensity of the beam to one half of its original value

Intensity/exposure/output

# of x-ray photons (3 terms mean this)

Inherent filtration

the filtration that is the result of the composition of the tube and housing (ex: thickness of the glass, oil in the tube, metal of the housing, etc.)

increases

As the tube ages, the inherent filtration ___

added filtration

filtration that is outside the tube and housing, but before the IR (image receptor), filtration that we contribute to the collimator

comes from the silver that is on the mirror in the collimator

where does added filtration come from?

total filtration

inherent + added

smaller

As kVp increases, a ___ percent of the beam or x-ray photons is absorbed through filtration

useful beam

Filtration also removes a percent of the ___

increase mAs

When we add filtration, we have to ___ to put more photons back into the beam

ancillary devices

additional tools

compound

uses 2 or more materials that compliment each other in absorbing materials

compound

composed of layers of materials with different atomic numbers, designed to absorb characteristic photons

radiation therapy

we use compound filter in ___

Thoraeus filter

has 3 materials: tin (highest 50), copper (29), and aluminum (made of different layers and different materials, highest atomic # faces toward x-ray tube)

compensating

filter that has differences in thickness, evens out body parts that are different in thickness or subject density, different absorbing abilities, match thin part of filter to thick part of anatomy and vice versa (improves image quality)

x-ray

We use compensating filter in ___

trough filters

designed for chest x-ray, thick part of filter matched with lungs, thin is matched to mediastinum, because air doesn’t absorb a lot

Boomerang filter

used for shoulder, compensating filter