beam restriction and filtration

what is the relationship between beam restriction and scatter

when BR increase, scatter decreases (inverse)

what is the relationship between beam restriction and IR exposure

when beam restriction increases, IR exposure decreases (inverse)

what is the relationship between bean restriction and contrast

when beam restriction increases, contrast increases (direct)

why is beam restriction important

it helps minimize exposure to the patient and provides the best image while limiting scatter

how can you improve image quality when scatter is created

by using a grid over the IR, which will absorb the scatter preventing it from reaching the IR

what is the relationship between kvp and transmission

when kvp increases, transmission increases as fewer photons undergo interactions with matter (direct)

what is the relationship between kvp and photoelectric absorption

when kvp increases, PE decreases due to the decrease in interactions (inverse)

what is the relationship between kvp and compton scatter

when kvp increase, scatter increase due to less absorption (direct)

what is the relationship between kvp and contrast

when kvp increases, contrast decreases due to scatter increasing (inverse)

what is the photoelectric formula

E_i = E_b + E_ke

what factors contribute to compton scatter

kvp, volume of irradiated material, and collimation

what is scatter caused by irradiated material affected by

the volume and the atomic number of the material

what controls the volume of the irradiated material

the field size and the patient thickness

what is the relationship between the volume of the irradiated material and scatter

when volume increases, scatter increases (direct)

what is the relationship between field size and the volume of the irradiated material

as field size increase, the volume increase (direct)

what is the relationship between patient thickness and the volume of the irradiated material

as patient thickness increases, volume increases (direct)

when are compression devices used

to decrease patient thickness

lower patient dose

decrease OID

uniform thickness

for mammo

what is the relationship between atomic number and scatter

when atomic number increases, scatter decreases due to absorption increases (inverse)

what is a collimator used for

to limit field size and as a light source to see where the CR is

what is inside the collimator

lead shutters

what is the purpose of the lead shutters inside the collimator

to control field size

reduce penumbra

reduce off-focus radiation

what is the positive beam limitation (PBL)

automatically adjust beam to the size of the IR

how does the bottom shutters reduce penumbra

bc they have a greater distance from the focal spot

how does the upper shutters reduce off-focus radiation

absorbs the radiation before it exits teh tube

what is off focus radiation

when electrons bounces off the focal spot and landing randomly

what is an aperture diaphragm

a flat sheet of metal with an opening in the center to attach the x-ray tube port

can also be cylinders and cones

what is the disadvantage of using aperture diaphragms

fixed field size

what are acniilary devices

lead blockers or lead masks used to help absorb scatter especially for large patients

what is another way to call filtration

hardening the beam

why is filtration considered hardening the beam

bc filters remove low energy level photons

what is the purpose of using filters

to reduce patient dose

why is aluminum used for filters

cheap, available, moldable, effective for removing low energy photons

what is Al thickness expressed as (units)

Al/Eq

what is the relationship between filtration and contrast

as filtration increase, contrast decrease due to the lack of absorption as low energy photons get absorbed by the body (inverse)

what is half-value layer (HVL)

the amount of absorbing material that’s reduced by half of the original value

how to find HVL (equation)

R or mR/2

what types of filtration are there

inherent, added, compound, compensation, total

what is inherent filtration

filtration from the composition of the tube and housing

what components of the tube contribute to inherent filtration

thickness of the glass envelope, the oil, glass window

what is the relationship between the tube gassiness and inherent filtration

the gassier the tube, the more inherent filtration due to the tube being coated by vaporized metal that absorb some of the beam (direct)

what is added filtration

filtration outside the tube but before the IR

what is an example of added filtration

the collimator

what is another term for compound filters

k-edge filters, bc each layer absorbs the characteristics photons created by the pervious layer

what are compound filters

filters made of 2 or more materials that help absorption

what is the order based on for compound filter layers

from highest atomic number to the lowest

the highest absorbs most of the low energy photons, but secondary reaction photons can produce but the lower layers absorb them

what is compensation filtration

filters used for unequal subject densities

what types of filters are considered compensation filters

wedges and trough filters

what is the goal for compensation filtration

to compensate for unequal absorption of the beam by making it more equal

what is total filtration

the inherent + the added filtration

what is the recommended total filtration for below 50 kVp

0.5 mm Al

what is the recommended total filtration for 50 - 70 kVp

1.5 mm Al

what is the recommended total filtration for above 70 kVp

2.5 mm Al

what is the relationship between filtration and IR exposure

as filtration increase, IR exposure decrease (inverse)

due to less IR exposure when using a filter, what needs to be done to compensate

increase technical factors to maintain same IR exposure