Physics Chapter 7 Flashcards
Know what classical interactions is also commonly called:
Coherent scattering or Thomson Scattering
Be able to describe what low energy atom does in classical scattering:
the incident x-ray photon interacts with an orbital electron of a tissue atom & change direction
KNow what happens when the energy from an atom in classical scattering is reemitted in a new direction
becomes a scatter photon
Be able to describe what the low energy causes in classical scattering
most classical scatter photons are absorbed in the body through other interactions & do no contribute significantly to the image, but do add slightly to patient dose
Know when Compton scattering commonly occurs in the diagnostic range
moderate energy x-ray photons (20-40 keV)
Know the 3 things a Compton interaction does
- Ionizes the atom making it unstable
- Ejected electron (Compton Electron/Secondary electron) leaves the atom with enough energy to go through interactions of its own in adjacent places
- The incident photon is deflected in a new direction and is now a Compton scatter
Know what the problem is with a Compton scatter interacting with the IR
it is not following its original path through the body & strikes the IR in the wrong direction **creates fog
Know what the most prevalent interaction between x-ray photons and the human body is
Compton scattering
Know what is responsible for most of the scatter that fogs an image
Compton scattering/interactions
Know what Compton scattering does NOT depend on
Atomic number
Know what the probability of Compton scattering is related to
Energy of the photon
Know what happens in Compton interactions as the x-ray photon energy increases
the probability of that photon penetrating a given tissue without interaction increases
Know in which direction Compton scatter photons can travel
any direction
Know what a deflection of zero degrees means with Compton interactions
means no energy transferred
Know what it represents with a 180 degree scatter deflection
maximum deflection and energy transfer
Know how much energy a scattered photon retains
Two thirds of its energy
Know where a Compton scattered photon can end up after exiting the patient
Near the patient/could expose the radiographer
Know where the major source of occupational exposure comes from
Compton scattering
Know the diagnostic range that photoelectric interactions occur
20-120 kVp
Know how photoelectric events occur
- Photoelectric interactions occur throughout the diagnostic range (20-120 kVp) & involve inner-shell orbital electrons of tissue atoms
- the incident x-ray photon energy must be equal to or greater than the orbital shell binding energy
Know what the x-ray photon does in photoelectric interactions
interacts with the inner-shell electron of a tissue atom & removes it from orbit
–The incident photon expends all its energy & is totally absorbed
Know what the absorption if the photoelectric interaction contributes to
Patient dose
Know what is necessary to create an x-ray
Although some absorption is necessary to create an x-ray image, it is the radiographers responsibility to select technical factors that strike a balance between image quality (needed absorption & transmission of x-ray photons to produce a good image) & patient dose
know the importance of the inner shell vacancy in photoelectric interactions
what makes the atom unstable
know what the source of secondary photons contributes to
patient dose
Know what the probability of photoelectric interaction depends on
the energy of the incident photons & the atomic number of the tissue atoms with which it interacts
Know what has to happen for photoelectric interactions to occur
the incident x-ray photon energy must be greater than or equal to the inner-shell binding energy of the tissue atoms involved
Know what happens in photoelectric interactions when the kVp is to high
less absorption takes place & some absorption is necessary for image formation
Know what the probability of photoelectric events is directly proportional to
the third power of the atomic number of the absorber
Know what the cubic relationship means to you the radiographer
when he or she makes small changes in the kVp setting or there are small changes in the atomic number of the tissue( anatomic variations or a pathologic condition) large changes in the probability of photoelectric events will result
In regards to photoelectric events what happens to tissues with higher atomic numbers
the greater the number of photoelectric events
In regards to photoelectric interaction photons what does bone do
more photons are absorbed, which means fewer photons are exposing the IR, resulting in the lighter shades on an image
Know what must be done in regards to photoelectric events if a structure isn’t visualized well on an image
contrast agents are added
Know when pair production occurs
only with very high energy photons of 1.02 MeV or greater
Know what happens in a pair production interaction
the interaction occurs when the incident x-ray photon has enough energy to escape interaction with the orbital electrons & interact with the nucleus of the tissue atom
Know why differential absorption is called “differential:
different body structures absorb x-ray photons to different extents
Know what absorption depends on
the density of body tissue in which photons are passing
