Chapter 7 Exam Flashcards
Radiographic density refers to overall _______ on image receptor
blackness
Classical interactions has 3 names:
classical, coherent scattering, Thompson scattering
What interactions and effects do we deal with the most?
classical interactions, Compton scattering, and photoelectric effect
Classical interactions result in:
scatter x-rays
high-energy photons interact with random electron and gets deflected in new direction
- Ionizes the atom (makes it unstable)
- Electron leaves the atom with enough energy to have an interaction with another atom close to it
- Results in image fog (also called noise)
- Happens a lot, not good
compton scattering interaction
x-ray photons are totally absorbed
photoelectric interaction
Increased tissue density _______ radiographic density
decreases
Decrease tissue density (ex: adding air) ________ radiographic densities because x-rays can get through easier
increases
Increasing tissue density ________ radiopaque
increases
Decreasing tissue density ________ radiolucency
increases
produces two particles-positron & electron, happens outside of diagnostic imaging
Pair production
Incident photon =
1.022 MeV (very big)
does not occur in radiography (10 MeV or more)
photodisintegration
gives us the ability to have different tissue densities and contrast in an image
The higher the Z number the more dense the atom is and the more likely it is to absorbs
differential absorption
____ creates more radiographic density
Air
_____ creates less radiographic density
Metal
Which of the following is a major source of occupational exposure?
Compton interactions
Which interaction, within the diagnostic range, does not involve the removal of an orbital electron?
Classical scattering
Which interaction requires 1.02 MeV of energy?
Pair production
A photon of 10 MeV colliding with a nucleus will likely result in what type of interaction?
Photodisintegration
Which technique will produce the greatest number of photodisintegration events in an average abdomen? 120 kV and 5 mAs, 108 kV and 10 mAs, 98 kV and 20 mAs, none of the above
None of the above
Which of the following events will not occur in the diagnostic range of x-ray energies? Classical, compton, photoelectric, photodisintegration
Photodisintegration
Positive contrast media is administered to increase what type of interactions?
Photoelectric
Which of the following contributes most to image fog? Classical, photoelectric, pair production, compton
Compton
Which interaction in the diagnostic range involves the total absorption of the incident photon?
Photoelectric effect
When the kV selected is equal to or slightly greater than the inner-shell binding energy of a target tissue atom, which interaction predominates?
photoelectric
- Also called coherent or
Thomson scattering - The incident x-ray
photon interacts with
an orbital electron of a
tissue atom and
changes direction - Incident wavelength
equal to scattered
wavelength - Energy below 10keV
(little importance to
diagnostic x-ray)
classical interactions
An incident x-ray photon
enters a tissue atom,
interacts with an orbital
electron, and removes it
from its shell; it loses up to
one third of its energy and
is usually deflected in a new
direction
compton interaction
compton interaction formula
Ei = Es + (Eb + Eke)
Ei = incident photon energy
Es = scatter photon energy
Eb = electron binding energy
Eke = photoelectron kinetic energy
ionizes the atom making it unstable
the ejected electron leaves the atom with enough energy to go through interactions of its own adjacent atoms
the incident photon is deflected in a new direction and is now a compton scatter photon with enough energy to go through other interactions in the tissues or exit the patient and interact with the image receptor
compton interactions
Is one of the most prevalent interactions between x-ray
photons and the human body in general diagnostic
imaging
compton scatter
Probability NOT dependent on the atomic number of
atoms involved but is related to the energy of the
photon
compton scatter
The incident x-ray photon interacts with the inner-shell electron of a tissue atom and removes it from orbit
photoelectric interactions
The tissue atom is ionized and the inner-shell vacancy makes the
atom unstable
To regain stability, a ________________ occurs, producing secondary x-ray photons
These secondary photons are of low energy, are absorbed by the body in other photoelectric events, and contribute to patient dose
characteristic cascade
photoelectric interactions
photoelectric interaction equation
Ei = Eb + Eke
Ei = Incident photon energy
Eb = Electron binding energy
Eke = Photoelectron kinetic
energy
The probability of photoelectric interaction
depends on the following:
The atomic number of the tissue atoms with which they interact
The incident x-ray photon energy
factors affecting the photoelectric-compton ratio
Z# of the material
Photon energy
Occurs when the incident x-ray photon has enough energy to escape interaction with the orbital electrons and interact with the nucleus of the tissue atom
pair production
Produces two
particles: a positron
and an electron
pair production
For these particles to exist, they must each
have energy of 0.51 MeV.
Both particles travel out of the atom.
The electron undergoes many interactions
before coming to rest in another atom.
The positron travels until it strikes an electron,
causing an annihilation event.
Does not occur in
radiography
pair production
Occurs when photons with extremely high energies strike the nucleus of the atom and make it unstable
The nucleus of the atom involved regains stability by ejecting a nuclear particle
Does not occur in radiography (10 MeV or more)
photodisintegration
The difference between x-ray photons that are absorbed photo-electrically versus those that penetrate the body
Different body structures absorb x-ray photons to different extents
differential absorption
those photons
that are attenuated by the
body and do not reach the
image receptor
absorption
those x-ray photons that pass through the body and reach the image receptor
transmission
factors affecting differential absorption:
higher atomic number (Z), increased kVp, increased mass density
what are the three most common effects in radiobiology:
main-chain scission
cross-linking
point lesions
which of the following is NOT one of the five basic x-ray interactions with matter?
bremsstralung
after compton scattering, the scattered x-ray has:
longer wavelength
the probability that an x-ray will interact with an outer-shell electron is influenced principally by:
the energy of the incident x-ray
the compton effect is:
independent of Z
which term describes how different body structures absorb x-ray photons to different extents?
differential absorption
how does a higher atomic number (Z) affect PE absorption?
increases PE absorption
how does a higher atomic number (Z) affect compton scatter?
compton scatter is unaffected
how does a higher atomic number (Z) affect transmitted x-rays?
decreased transmitted x-rays
how does higher kVp affect PE absorption?
decreases PE absorption
how does higher kVp affect compton scatter?
relatively increases compton scatter
how does higher mass density affect PE absorption?
increases PE absorption
how does higher kVp affect transmitted x-rays?
increases transmitted x-rays
how does higher mass density affect compton scatter?
increases compton scatter
how does higher mass density affect transmitted x-rays?
decreases transmitted x-rays
