Xray physics WK5 Flashcards
cathode does what with e-?
emits them
anode has 2 parts
target face & focal spot
smaller focal spot could not be good due to
heat energy
as the e- cross from the cathode to the anode what is created?
a circuit
the job of the rotor
is to distribute heat over larger surface area
due to the target angle on the anode side what happens to the appearance of the focal spot
it appears smaller
anode heel effect*
anode heel = thins edge of disk
interference of the heel of the anode and the emission of xrays going towards it
when some x-rays are absorbed by the anode heel it is known as what effect?
anode heel
reductions of xray photon intensity toward anode side is due to the
anode heel absorbing it
as the collimated field increases what happens to the effect of the xray photons?
have a greater effect
smaller the focal spots has what affect on the heel effect
greater the intensity change
for a upright tube what position is the anode and cathod
anode is up and cathode is down
tube failure is due to
heat
how is heat generated
using higher voltage and amperage
maximum exposures should not be made in what situation when considering the condition of the anode?
a cold one
what should we do before taking a large xray of the lumbar
pre-heat with small exposure first to avoid anode damage
projectile electrons meaning that the e- are coming from
the cathode
in an xray what is kinetic energy changed to and how?
xray energy and this is done by the cathode e- striking the tungsten atoms of the anode
what % of the kinetic energy is changed to xray?
1
2 different mechanism for xray production
characteristic & bremstrahlung
for tungsten how much kVp in order to move e- out of K shell?
69
ionization by removal of K shell electrons occurs how
BE must be overcome,
the voltage potential between anode and cathode ust be at least 69 kVp in order to deliver projectile e- with 69 kEv
inner shell vacancy is filled by
electron from an outer shell
to figure out kEV you substract what of the shells?
BE of shells
when e- move –> what is produced?
energy as an xray and the energy will be the same and characteristic of tungsten
what is the characteristic pattern of tungsten?
the movement of a e- from a nearby shell into the vacant one –> generating xray energy
photons, where do they go
everywhere
bremstrahlung means
brems = brakes strahlung= ray or radiation
bremstrahlung is the interaction between what kind of e- and atom?
projectile e- which is negatively charged and the the electromagnetic field of the nucleas of the tungsten atom which is positively charged
Bremstrahlung:
as the projectile e- changes course and passed by the nucleus what may occur?
- May lose some or all of its kinetic energy
- ->If enough energy is lost, it is expressed as x-ray photon
Bremstrahlung:
as the projectile e- changes course what occurs?
it released energy
Bremstrahlung:
as the projectile e- moves closer to the nucleus what occurs?
it will release more energy
can 2 projectile e- that are at the same distance have produce different energies?
yes
At a given tube potential (eg, 70 kVp), every projectile electron does/may not have 70 keV energy
..why?
due to voltage ripples
Characteristic spectrum characteristics
shows discrete bands of photons at specific energy levels
Bremstrahlung spectrum characteristics
(bottom) shows continuous range of x-ray photon energies
the peak of the bremstrahlung peak of spectrum graph is what fraction of the maximal value?
1/3
average photon energy
quality of the xray beam
Possible effects on emission spectrum
Beam Quality change
Beam Quantity change
Beam Quality change =
a change in the average photon energy
Recall that it is beam quality that determines the penetrating ability of the beam
Beam Quantity change =
a change in the number of photons in the beam
This is equivalent to “beam intensity”
Variables affecting the x-ray emission spectrum include:
Tube voltage (peak voltage = kVp and voltage ripple)
mA
filtration
as the voltage is high what happens to quality and quantity ?
it is also high
Less voltage ripple results in more
efficient production of useful x-ray
to production of less “soft’ x-ray has what affect on the pt. dose?
reduced
as the voltage ripple decreases emission spectrum does what?
it increases
amperage
number of e- that are moving in circuit
does the quality change when the mA increases?
no
does the quantity change when the mA increases?
yes it increases
as kVp changes what else chages?
both quality and quantity
does bremstrahlung have more energy to lose?
yes
what do higher energy photons do
they go through stuff better = more exposure being high
if the quality of photons increase
more photons get absorbed
kVp rule states that what % is needed to increase the receptor exposure by _____ the amount?
15% rule, by 2
15% rule states that
a 15% increase of kvp will aprox. double image receptor exposure
what two thighs have the same effect on the emission spectrum?
time & mA
mAs is a term to describe
a result of mA and time combined
as long as the kVp is constant what can you rely on?
these exposures make same amount of radiation with same distribution of photon
any equal combination of mA and time will have what kind of effect on exposure together?
they will have exactly the same emission spectrum
Passing an x-ray emission through higher filtration will result in?
Beam hardening
what occurs at the tube when voltage changes?
beam quantity
as you increase the mA does the quantity or quality change of the beam?
quantity
