Ch. 8 X-ray emission Flashcards
What is the intensity of the x-ray beam of an x-ray imaging system measured in in air?
mGy(subscript a) formerly milliroentgen
What is mGy (air) called?
x-ray quantity
x-ray quantity and radiation exposure are both measured in…
mGy (air) or mR
mGy measures what in the air?
the number of ion pairs produced in the air by a quantity of x-rays.
X-ray quantity is the number of…
x-rays in the useful beam
Most general purpose radiographic tubes, when operated at 70 kVp produce x-ray intensities of about…
50 microgray/mAs or 5 mR/mAs at a 100cm SID
x-ray quantity is directly proportional to…
mAs
formula for relationship of mAs to quantity
I(1)/I(2) = mAs(1)/mAs(2)
x-ray quantity is proportional to the square of the ratio of…
kVp
formula for relationship of kVp to quantity..
I(1)/I(2) = (kVp(1)/kVp(2))^2
to maintain constant exposure of the IR, kVp should increase by ___ and mAs should…
15%, decrease by 50%
DESCRIBE inverse square law.
x-ray intensity varies inversely with the square of the distance from the x-ray tube target
Formula for inverse square law?
I(1)/I(2) = (d (2)/d (1))^2
To maintain constant exposure when SID is increased, mAs should be…
increased by SID^2
What is the formula for the square law?
mAs (1)/mAs (2) = SID(1)^2/SID(2)^2
DESCRIBE the square law
When SID is increased, mAs must be increased by SID^2 to maintain constant exposure to the IR
How much filtration is positioned in the useful beam in a metal filter?
1-5 mm of Al
Adding filtration to the useful beam reduces…
patient dose
As the energy of an x-ray beam is increased, the penetrability is…
also increased
What does penetrability refer to?
the ability of x-rays to penetrate deeper in tissue
Penetrability of a beam is also called…
x-ray quality
What do not affect radiation quality?
Distance and mAs
Attenuation is…
the reduction in x-ray intensity that results from absorption and scattering
How is the quality of x-rays measured?
by the HVL.
