Characteristics of X-rays Flashcards
two mechanisms of x-ray production
- bremsstrahlung
- characteristic radiation
what is bremsstrahlung x-ray production?
electron to nucleus interaction
what is characteristic radiation?
electron to electron radiation
bremsstrahlung: x-rays produced when ______ are suddenly _____ when they pass close to the nuclei of a ________
high velocity e-, decelerated, high Z# absorbing material
3 requirements of Bremsstrahlung radiation
electrons, high velocity to electrons, high Z# absorbing material
bremsstrahlung has _____ and ___ interactions
direct hit, near-miss
because not all e- attain the same ___, some move at different ___ than others, ultimately producing _________, or__________
velocity, velocities, radiation of different energies, polychromatic x-ray beam
what percentage of diagnostic beam is bremsstrahlung?
70%
in near-miss bremsstrahlung interactions: the closer the e-, the ________ of the bremsstrahlung photon
closer the electron
characteristic radiation: a number of e- with inner orbital electrons of W, overcome the ______, and cause _____
binding energies, ionization
result of characteristic radiation is a polychromatic x-ray beam but __________ than bremsstrahlung
much narrower energy spectrum
the energy of characteristic radiation is specific to ________
the Z of the producing material
what percentage of diagnostic x-ray beam is characteristic?
30%
incident electron knocks ______ (____); incident electron may continue as a ______
inner electron out (recoil electron), photoelectron
are x-rays electrons?
no
electrons are….
- particulate radiation
- have mass
- and have variable velocity
x-rays are…
-electromagnetic radiation (no mass, fixed velocity)
radiation that originates at focal spot, leaves the tube through window, is useful in image formation
primary (usable) beam
radiation that originates at focal spot, leaves the tube through barriers around the tube
leakage radiation
radiation that originates in tissues, causes image noise
secondary/scatter radiation
what is used to minimize leakage radiation?
glass, oil, and metal enclosures
change in kVp changes ________
potential difference between cathode and anode
increase kVp does what to the number of photons generated (quantity)?
increases quantity
increase kVp does what to the mean energy of the photons (beam quality)?
increases quality
increase kVp does what to maximal energy of photons (beam quality)?
increases quality
increase kVp does what to radiographic contrast?
decreases contrast
For constant receptor exposure, exposure time and kVp are ________
inversely related
when kVp is increased, ____ should be decreased
exposure time
most times, we “set and forget” _____ while we change ____
kVp and mA; exposure time
increase mA, what happens to amount of power applied to filament?
increased
increase mA, what happens to x-ray beam quality?
increasing mA does nothing to beam quality
what happens to receptor exposure when we increase mA?
increase exposure
exposure time does not influence ______
energy of the photons
mAs is a product of ______(__) and _______(_)
tube current (mA), exposure time (s)
what is the control of size/shape of x-ray beam?
collimation
increased collimation leads to…
smaller beam, decreased receptor exposure
- circular, diameter at end of cone = ____
- rectangular end of cone = ____
circular = 2.76" rectangular = 2.0"
a rectangular collimation reduced ______
patient exposure/dose substantially
purpose of filtration
preferentially remove long wavelength photons
lower kVp results in _______, but the longest wavelength are not useful in _______; they increase patient dose/radiation hazards and _____
higher radiographic contrast, image formation; must be removed
_____ + ______ = total filtration
inherent + added
examples of inherent filtration
widow of x-ray tube, insulating/cooling oil, oil seal
examples of added filtration
aluminum discs (1/2mm or 1mm)
beam produced at or below 70kVp = ___mm Al equivalent
1.5mm
beam produced at 90 kVp = ___mm Al equivalent
2.5mm
if filtration increase, mAs should be ____ to ________
increased, maintain similar receptor exposure
the thickness of a material which, when placed in the path of an x-ray beam, will reduce quantity of radiation by 50%
half value layer (HVL)
HVL is an indicator of x-ray beam _____
quality (penetrability)
a beam with higher mean energy (higher penetrability) has a _____
thicker HVL
you need to increase HVL with…
increased kVp, increased filtration
for constant receptor exposure, exposure time should be ____ when SID (source to object distance) increases
increased
based on inverse square law, exposure time is ______ to the square of SID
directly proportional
with inverse square law, if you double the distance, intensity becomes ____ the original
1/4
with inverse square law, if you half the distance, intensity becomes ____ the original
4x
attenuation in which photon ionizes absorber (tissue) atoms, convert their energy to ejected e-, and then cease to exist
absorption attenuation
attenuation in which photons interact with
absorber (tissue) atoms, but is deflected in
another direction
scattering attenuation
3 types of beam attenuation
- coherent scattering
- photoelectronic absorption
- Compton scattering
how many photons undergo coherent scatterin?
7%
how many photons undergo photoelectronic absoprtion?
27%
how many photons undergo Compton scattering?
57%
did you look at the 3 types of beam attenuation photos on the powerpoint?
I hope you did, they sure help!
coherent scattering process
- low energy incident photon interacts with whole photon
- atom momentarily excited; photon momentarily disappears
- excited atom returns to ground state; release photon
- photon absorbed by tissue
coherent scattering has a (contribution/no contribution) to image noise
no contribution
______ and _____ cause secondary and tertiary ionizations
photoelectric absorption and Compton’s scattering
photoelectric radiation process
- Incident x‐ray photon interacts with an inner
orbital electron - Inner electron is ejected; called photoelectron
or recoil electron (atom is ionized) - higher orbital e- falls to fill vacancy
- this “fall” emits electromagnetic energy
Compton’s scattering process
- Incident photon interacts with an outer orbital e-
- Overcomes binding energy, ejects e- (ionization)
- Ejected e- (called Compton’s electron)
acquires part of the energy - Remainder of energy given off as scattered,
weaker energy photon
