Ch 8 X-ray Emission Flashcards
intensity of the beam is measured in _____ aka _____
mGya (mR) aka quantity or radiation exposure
mGya (mR) is a measure of:
the number of ion pairs produced in air by a quantity of x-rays
radiation exposure rate is expressed in ____ and can also be used to express ______
mGya/s, mGya/min, mGya/mAs and can also be used to express x-ray intensity
*x-ray quantity is the ____
number of x-rays in the useful beam
x-ray quantity is _____ to mAs
directly proportional
the change in x-ray quantity is proportional to the _____
square of the ratio of the kVp
if kVp were doubled the x-ray intensity would:
increase by a factor of 4
*x-ray quantity is proportional to:
the kVp squared
doubling the x-ray intensity by kVp alone requires:
an increase of 40% in kVp
an increase of 15% in kVp will _____ the mAs and should be accompanied with _____
double the mAs, a reduction of one half the mAs
by increasing kVp and reducing mAs so that IR exposure remains constant, the patient dose ______; the disadvantage when the film is the IR is _______
is reduced significantly; reduced image contrast
x-ray intensity varies inversely with the _____
square of the distance from the x-ray tube
*x-ray quantity is inversely proportional to the _____
square of the distance from the source
*when SID is increased, ___ must be increased by ____ to maintain constant exposure to the IR
mAs must be increased by SID^2
the purpose of filters is to:
reduce the number of low-energy x-rays
*adding filtration to the useful beam reduces:
patient dose because fewer low-energy x-rays are found in the useful beam
x-ray beam hardening increases:
the number of high energy x-rays in the beam by removing the lower energy non penetrating x-rays
penetrability aka ____
quality
*penetrability is the ability:
of an x-ray beam to pass through tissue
______ and _____ do not affect radiation quality; they do affect radiation quantity
distance and mAs
x-rays of any given energy are more penetrating in _______
material of low atomic number
*attenuation is:
the reduction in the x-ray intensity that results from absorption and scattering
quality of x-rays is measured by the ____
HVL
HVL is a characteristic of the:
useful beam
HVL ranges from:
3-5 mm Al or 3-6 cm soft tissue
*the HVL of an x-ray beam is the:
thickness of absorbing material necessary to reduce the x-ray intensity to half its original value
*HVL is the best method for:
specifying x-ray quality
*x-ray beam quality can be identified by ___ or ____, but ____ is most appropriate
kVp or filtration, but HVL is the most appropriate
*increasing kVp increases:
the quality of the beam
an increase in mAs:
increases quantity alone
an increase in kVp:
increases both quantity and quality
an increase in distance:
reduces the quantity and does nothing to the quality
an increase in filtration:
reduces the quantity and increases the quality
*increasing filtration increases:
the quality of the beam
filtration of diagnostic x-ray beams has 2 components:
inherent and added filtration
inherent filtration:
is approximately ____ equivalent
the glass or metal enclosure of the x-ray tube filters the emitted beam
is approximately 0.5 mm Al equivalent
added filtration:
a thin sheet of Al positioned b/w the protective x-ray tube housing and the x-ray beam collimator
*added filtration results in:
increased HVL
the addition of a filter to an x-ray beam:
attenuates x-rays of all energies emitted, but it attenuates a greater number of low-energy rays
compensating filters:
are useful for:
compensate for differences in subject radiopacity (body parts that vary greatly in thickness or tissue composition)
are useful for maintaining image quality
*SID changes will affect _____ not _____
quantity NOT quality
*the higher the mm filter it is, the _____ the penetration of the beam (higher HVL)
greater
*when operating on <50 keV you need ____ total filtration
.5 mm Al
*when operating on 50-70 keV you need ___ total filtration
1.5 mm Al
*when operating on 70+ keV you need _____ total filtration
2.5 mm Al
*less filtration is necessary at ____ energy
less
*the mirror of the collimator is _____ Al and a part of _____ filtration
1 mm Al and a part of added filtration
*the tube proper is ____ Al and a part of ______ filtration
.5 mm Al and a part of inherent filtration
*with filter wedges you want the _____ mm at the ____ part
thinner mm at the thicker part
*total filtration = ______+______
added + inherent
*photoelectric effect has the _____ B/W/Grays
Compton scatter has the ____ B/W/Grays
photoelectric good B/W/Grays
Compton bad B/W/Grays
*the higher the Z the _____ the absorption
higher
*the _____ the gray the more absorption
lighter gray
*the _____ the mAs density the more absorption
greater
*as energy increases ____ is more common than _____
Compton is more common than photoelectric
