week 6 Xray physics up too chapter 10 Flashcards
higher energy photons are produced by increasing what?
KVp
as you increase filtration what is affected?
‘beam hardening’
decreases the xray energy keV by absorbing the lower energy photons
inherent filtration
is built into the machine to remove the low energy photons
added filtration is done when you need?
to balance the intensity of x-ray exposure over an area of anatomy that is not uniform in density and/or thickness
what portion of the wedge is over the thin part of the thoracic spine?
the thick part
collimator is set to go straight through?
the dense part of the anatomy of the pt.
Penetrability =
ability of x-ray beam to penetrate
Attenuation =.
reduction of beam intensity due to absorption and scattering
of photons not quality
Half-value layer (HVL) =
that thickness of absorbing material that will cause the exiting beam intensity to be one-half of the entering (ie, incident) beam intensity
uniform attenuation is not seen in what kind of imaging?
diagnostic xray beam
For a beam NOT composed of monoenergetic photons, what actually happens to the half-value layer as the beam passes thru matter?
becomes thicker as the beam passes through matter
what do you think a tenth-value layer would be?
reduce it too a 10th of that value
Five basic interactions may occur betweeen matter and xray
Coherent scattering Photoelectric interaction Compton interaction Pair production Photodisintigration
photons of electromagnetic radiation tend to interact with structures similar in size to their ________?
wavelength
Low energy photons (longer wavelength) tend to interact with
atoms
Moderate energy photons tend to interact with
electrons
Higher energy photons tend to interact with
nuclei
“classical scattering” or “Thompson scattering”
occurs at what energy levels?
photon energy levels below 10keV
coherent scattering affects what amount of xray photons?
small amount
during coherent scattering the xray energy is ______ and ________ from the atom
- absorbed
2. re-emitted
pair production?
Photon disappears and 2 oppositely charged pieces of matter (one electron and one positron) are formed
what is the Photodisintigration energy level
& this is between what two structures?
(>10MeV) photon and nucleus
pair production energy level between what two structures?
Interaction of high energy (>1.02MeV) photon and electromagnetic field of nucleus
in photodisintigration what happens to the photon?
Photon disappears a nuclear fragment is emitted
Photoelectric interaction?
Interaction of lower energy photons in the diagnostic x-ray beam
does ionization occur during Photoelectric interaction?
yes, the photoelectron is ejected
Photoelectric interaction involves electron from where atomic orbit?
inner shell
what absorbs the energy of the xray?
inner shell electron due to
KE + BE is equal to what?
the energy of the xray
the photon that is produced in the photoelectric interaction?
secondary xray photon produced by xray not inside the tube (tungsten)
is all of the energy absorbed in photoelectric interaction?
yes
probability of photoelectric interaction is dependent on?
energy of the xray and the atomic number of the atom involved
relationship of the xray energy and PE event?
inversely proportional to the 3rd power of the xray energy
atomic number and PE relationship?
directly proportionally to the 3rd power of the atomic number (z#)
compton interaction involves?
photons within the diagnostic spectrum that have intermediate to high energy
in compton interaction the incident photon interacts with the
outer shell e-
does ionization occur in compton?
yes
what is the characteristic of incident photon in comptone?
scattered
scattered photon means?
redirected from their original vecter and contains 2/3 or more of the incident photon NRG;
with minimal direction change of a e- what happens to the energy loss
it will be minimally loss
are scattered photons useful in image production?
no
what is the caution of scattered photons?
potential to have othoer ionizing events to go on so they are hazardous
Atomic number of the involved atom _____ affect Compton interaction probability
does not
as compton interactions decrease what happens to the photon energy?
it will increase
why are compton interactions more predominant when the average beam energy increases?
because photoelectric energy decreases more in xray energy; in turn increasing chance of compton interaction
how do you control photon energies?
with kVp
at about 80 kVp what is happening in regards to compton vs photoelectric?
about equal to eachother
which one predominates at higher kVp in comparison to compton and photoelectric?
comptom
differential absorption defintion?
difference in the absorbing ability between 2 different materials
what influences the differential absorption (photoelectric interactions)?
the atomic energy
as you from fat > soft tissue > lung > bone what happens to the atomic number?
it increases
* little difference between fat and other soft tissue
how can you use contrast materials?
use the ones with greater atomic number to give an outline.
what is the difference between compton interaction and photoelectric interactions in reagards to diagnostic imaging?
compton: does not contribute
Photoelectric: does contribute
photoelectric interactions effect attenuation in what way?
they play a big role in it by decresing the number of photons as it goes through tissues
how does scatter e- effect the attenuation?
decreases the # of photons in the beam with some backscatter
mass density?
how many atoms are present per unit volume of material
