radi 462 filtration & filters lecture + first 5 slides from interactions & attentuation

reduction in the intensity (quantity or number) of photons as xrays transverse matter

attenuation

which type of photons are attenuated

absorbed or scattered, NOT transmitted

since the percentage the photon intensity decreases is constant, this results in _

exponential decrease in the intensity

transmitted intensity =

initial intensity x e^-coefficient(thickness of material)

constant percentage decrease in energy, no change in average energy with which type of beam

monoenergetic

for monoenergetic attenuation curve, if you double thickness of material, intensity/quantity is reduced by ?

half

thickness of material it takes to reduce the beams intensity by half

HVL (half value layer)

2nd layer needs to be _ due to beam hardening

thicker/larger/greater than 1st layer

purpose of filtration/filter

reduce ESE (entrance skin exposure)

filtration recommendations from who

NCRP (national council on radiation protection)

filtration regulations from who

CFR (code of federal regulations) —> FDA

which components are inherent filters

tube window, oil, tube port cover, collimator mirror

filtering mechanisms added to the beam to meet regulatory requirements

added filtration

examples of added filtration

aluminum (most common), compound filter (k-edge, stack, composite); goes between collimator and protective housing

compound filter has metals stacked in _ atomic number order, with the _ atomic number towards the top/tube

decreasing, highest; usually copper than aluminum

1.5 mm Al Eq

inherent filtration; tube window, oil, tube port cover, collimator mirror

1.0 mm Al

added filtration; aluminum usually, sometimes compound

2.5 mm Al

minimum total filtration

NCRP minimum tube filtration kVp below 50

0.5 mm Al

NCRP minimum tube filtration kVp 50-70

1.5 mm Al

NCRP minimum tube filtration kVp above 70

2.5 mm Al

tube filtration (can/cannot) be directly measured

cannot; beam penetrability provides way to assess adequate filtration

_ used to quantify beams ability to penetrate material and verify adequate filtration

HVL

only filter that doesnt attach to collimator is ?

boomerang; goes underneath pt, shoulder image

name the 5 compensating filters

wedge, trough, mediastinal, ferlic, boomerang

most likely to use which compensating filter

ferlic; cross table hips, cervical spines

K shell is the _ shell

innermost

x-rays that exit the tube

primary radiation

pass thru body without interacting

transmitted xrays

photoelectric are

absorbed

compton and coherent are

scattered

create the low or dark areas of luminance; useful information

transmitted xrays

create the high or light areas of luminance; allows structures to be visualized; attenuated via photoelectric; useful information

absorbed xrays

decrease image contrast and quality; attenuated via compton; useless information, can’t prevent but can minimize; greyness on an image

scattered xrays

which type of xray has no impact on the image

coherent/classical

difference between xrays that are absorbed and those that are transmitted, thus creating the image

differential absorption/attenuation