Attenuation of X-rays Flashcards
(45 cards)
what happens to X-rays when they hit the patient
- Scattered and contribute to fogging
- absorbed completely in patient
- pass through without interacting with the tissue atoms
what is light and dark on an X-ray
Light: photons absorbed
Dark: photons pass through
In the diagnostic X-ray energy range, the interactions are what types
Coherent scattering
Photoelectric absorption
Compton scattering
what happens to X-rays in a beam path
Either absorbed or scattered
what do photons do in absorption interactions
Photons ionize absorber aoms
what do photons do in scattering interactiosn
interact with absorber atoms but then are scattered in another direction
what allows us to see differences in a radiograph
The differential exposure due to scattering and absorption
what are the means of beam attenuation
Photoelectric absorption
coherent scattering
Compton scattering
what percent of primary photons do what when in a patient
No interaction: 9%
Coherent scattering: 7%
Photoelectric absorption: 27%
Compton scattering:57%
what is the interaction in coherent scattering
- Low energy photons interact with outer electons causing the outer shell to vibrate momentarily at the same freqeuncy of incoming photon
- incident photon ceases to exist
- entire energy given off as scattered photon to be absorbed by tissue
what does the Coherent scattering ultimately do to the incident X-ray photon
Direction is altered
what happens in Photoelectric Absorption
- Incident photon interacts with an inner electrons (K)
- overcomes binding energy of electron and electron is is ejected (ionization)
- ejected electron acquires the remainder KE from the photon
what is the elctron called after it is ejected
Photoelectron or recoil electron
what happens to the elctron deficiency from photoelectric absoprtion
K shell electron deficiency is instantly filled with an L or M shell electron with release of charcteristic radition
what is the strength of the radtion due to filling of K shel electrons from L and M shell electrons
Low energy that does not fog image
what is the frequency of the photoelectric related to concerning to the photon energy
inversely proportional to the cube of photon energy (higher energy photons are less likely to undergo absorption
how does the frequency of photoelectric interactions relate to atomic number
directly with the thrid power of the atomic number of the absorber (as z increases, more photoelectric absorption)
how much more likely is bone to absorb by photoelectric interaction compared to soft tissue
6.5 times greater
what is the importance of different photoelectric interactions
different density in radiographic images
what happens to recoil electrons released via the photoelectric effect
travel short distace in the absorbed before they give up energy (absorbed by patient)
how does the absorption of recoil electrons due to the photoelectric effect by the absorber help produce high-quality radiographs
No scattered raditation fog in the recepor
how does the absorption of recoil electrons from the photoelectric affect affect the patietn
Bad for patients due to increased radition absorption
How does Compton’s Scattering occur
- Incident photons interact with an outer electron
- electronic is ejected (compton’s electron) aquiring part of KE
- remaineder of energy given off as a scattered photon
what does the compton’s electron do
Causes secondary and tertiary ionization
