chapter 3 EXAM 2 Flashcards
milliampere seconds mAs
quantity
product of exposure time and tube current
a measure of the total number of electrons that travel from the cathode to the anode
peak kilovoltage kVp
quality
controls the quality or penetrating power of the photons in xray beam
when radiation interacts with matter (the body) some photons are….
some photons are absorbed
some are scattered and some pass through without interacting at all
absorption
transference of electromagnetic energy from an xray beam to the atoms or molecules of the matter through which it passes
scatter
a change in direction of travel of an xray photon that may also involve a potential loss of radiation energy
absorption + scatter =
attenuation
direct transmission
when photons pass through the patient without interacting and reach the IR
primary radiation
emerging xray photon beam
indirect transmission
primary photons that undergo compton and or coherent interactions and are scattered or deflected after they go through an object
an optimal xray image is formed only when
direct transmission xrays reach the IR
a radiographic image is formed from
directly transmitted photons and indirectly transmitted (scattered) photons
attenuation
refers to any process decreasing the intensity of the primary photon beam
radiographic fog
undesirable additional density on a radiographic image caused by scatter reaching the IR
true or false
photon interaction is random
true
an xray image results from the difference between
the xrays absorbed photoelectrically by the patient and those transmitted to the IR
differential absorption
different degrees of absorption in different tissues that result in image contrast and formation of the image
what are the 4 factors that influence probability of interactions of photons
- photon energy
- atomic number
- mass density
- tissue thickness
as photon energy increases,
kvp increases and absorption is reduced
as atomic number increases,
it increases the chances that the xray photon will be absorbed to the 3rd power
as xray energy increases
fewer compton interactions
fewer photoelectric interactions
more passing through without interacting
as tissue atomic number increases
no change in compton interactions
more photoelectric interactions
less passing through without interacting
as tissue mass density increases
proportional increasie in compton interactions
proportional increase in photoelectric interactions
proportional reduction in passing through without interacting
5 types of interaction between x radiation and matter
- coherent scattering
- compton scattering
- photoelectric absorption
- pair production
- photodisintegration
coherent scattering is also called
classic, elastic or unmodified scattering
coherent scattering
involves low energy photons below 10 KeV
when the low energy photon interacts with tissue, it does not loose energy. It just changes direction and becomes excited.
no ionization occurs here.
photoelectric absorption is the most important
mode of interaction between xray photons and the atoms of the pts. body for producing useful images
photoelectric absorption
interaction between the dray photon and an inner shell electron (k shell)
to dislodge an inner shell electron from its orbit, the xray photon must
be able to transfer a quantity of energy equal to or greater than the electron binding energy
on interacting with the inner shell electron, the xray photon surrenders
all of its energy to the orbital electron and ceases to exist
it gets absorbed
the ejected electron is called a
photoelectron
auger effect
process that can occur as a result of photoelectric interactions
occurs when an inner shell electron is removed from an atom causing an inner shell vacancy
what are the byproducts of photoelectric absorption
photoelectrons
characteristic xray photons
probability of occurrence of photoelectric absorption depends on
the energy of the xray photons and the atominc number of the atoms it interacts with
photoelectric absorption increases to the 3rd power dramatically as the
energy of the incident photon decreases.
the probability of photoelectric absorption increases dramatically when
the atomic number of the atoms increases
when mass density is doubled, the chance for xray interaction is doubled because
twice as many electrons are available for interaction
the interaction of xrays with tissues is proportional to the
mass density of the tissue
T or F
if 2 structures have the same mass density and atomic number, but one is twice as thick, the thicker structure will absorb twice as many photons
True
T or F
the less a given structure attenuates xrays, the darker its radiographic appearance
true
the greater the difference in the amount of photoelectric absorption, the greater the
contrast will be between adjacent structures of differing atomic numbers.
as absorption increases, so does
the patient dose :(
compton scattering is also called
incoherent scattering
inelastic scattering
modified scattering
what is compton scattering
the interaction of xrays with matter that is responsible for most of the scattered radiation produced during radiologic procedures
process of compton scattering
incoming photon interacts with loosely bound outer shell electron. it surrenders part of its energy to dislodge the electron ionizing the atom
the ejected electron in compton scattering is called
compton scattered electron
secondary electron
recoil electron
what can happen to the compton scattered photon
it can interact with other atoms
it may emerge from the pt. and reach the IR causing fog
it could emerge from the pt. and expose personnel
compton scattering is the source of
most of the occupational radiation exposure that radiographers receive
the probability of the compton scattering effect does not depend on
the atomic number of the atom
doesn’t matter what it hits. it will effect an atom of soft tissue the same way as an atom of bone
compton scattering provides no useful info on the radiograph. it results in
reduced image contrast
Pair production does not occur unless
energy of the incoming xray photon is at least 1.022 mega electron volts
this is far above the energy used in diagnostic radiology
pair production process
incoming photon interacts with the nucleus of an atom of biologic tissue and disappears
in the process energy of the photon is transformed into 2 new particles
what are the 2 new particles the photon is transformed into in pair production
negatron (ordinary electron)
positron (positively charged electron)
annihilation event
the positron and the electron it interacted with are destroyed and their energy is converted into 2 xray photons that radiate out of the atom
photodisintegration
energy above 10 Megaelectron volts
energy too high for diagnostic radiation
process of photodisintegration
high energy photon collides with the nucleus of an atom and the nucleus emits a neutron
this makes the nucleus radioactive
