RADT 142 Module 14: Filtration and Ionization in Radiology

x-ray quantity is the amount of radiation reaching an

IR (image receptor)

radiation coming out of the x-ray tube is measured in

R or mR

radiation exposure or radiation intensity is the

primary beam coming out of the x-ray tube

primary controlling factor of quantity

mAs

secondary controlling factor of quantity

- kV

- distance

- filtration

mA relationship to quantity (DIRECT)

when we increase the number of electrons being boiled off, we increase the number of x-ray photons

kV relationship to quantity (DIRECT)

when we increase kV, we increase the speed at which electrons are being boiled off, therefore we increase the number of x-ray photons

distance relationship to quantity (INVERSE)

as distance increases, the number of x-ray photons hitting the IR decreases by the square of the distance

filtration relationship to quantity (INVERSE)

as filtration increases, the number of x-ray photons decreases

a 15% increase in kV is the same as _____ the mAs

doubling

a 15% decrease in kV is the same as ______ the mAs

halving

when we increase the kV by 15% we have to _____ the mAs to _____ the density

- 1/2

- maintain

when we decrease the kV by 15% we have to _____ the mAs to _____ the density

- double

- maintain

underexposed means we need to ... to increase the density

increase the kV by 15% or double the mAs

(remember both of these are the same thing)

overexposed means we need to ... to decrease the density

decrease the kV or 1/2 the mAs

if we want to maintain the same density we have to change ______ factor(s)

BOTH

remember

when we want to increase or decrease the density we only have to alter one factor bc changing one will alter the density

if the kV is increased by 15% the mAs is _______ to maintain the same density

1/2

if the kV is decreased by 15% the mAs is ______ to maintain the same density

doubled

as the quality increases the penetrating quality

increases

primary factor of quality

kV

secondary factor of quality

filtration hardens the beam therefore the quality of the beam increases (increases the average kV of the beam)

HVL (half value layer)

amount of absorbing material necessary to reduce the beam to 50%

as HVL increases

the quality increases

types of filtration

inherent and added

inherent filtration

in the x-ray tube and absorbs lower energy photons with the oil or x-ray housing

inherent filtration aluminum

0.5 mm Al equivalent

added filtration

filtration that is added to the port/window of the x-ray tube

added filtration aluminum

2.0 mm Al equivalent

total of inherent added filtration / total of filtration in the x-ray tube

2.5 mm Al equivalent

compensating filters types

wedge, trough

compensating filters

compensate for different tissue size types (chest) (ankle)

ionization chambers

used to measure ionization in the air

3 types of ionization chambers

- victoreen R meter

- cutie pie

- geiger-muller

victoreen R meter and where is it used in

under the x-ray beam and tells the R or mR in the air

diagnostic radiography

cutie pie

geiger-muller

detects radiation in nuclear medicine

grenz rays

extremely low x-ray photons that do not penetrate

grenz rays kV

10-15 kV