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Imaging1 chap12

Imaging1. x-ray interactions

QuestionAnswer
What is attenuation? Reduction in the number of photon in the beam, and a subsequent loss of energy as the beam passes through matter. -is the result of x-ray photons interacting with matter and losing energy from these interactions
In the diagnostic x-ray range, most commonly the interactions are with ? orbital electrons/intermediate-energy photons
The farther an electron is from the nucleus, the ___ the total energy of the electron will be. higher
The k-shell electrons have the _____ energy total, with the ___ binding energy. lowest energy, highest binding energy.
When a photon is absorbed, what happens to all of the energy of the photon? It is transferred to the matter and the photon no longer exists.
Coherent scatter is most predominant in what energy range? Low
When does photoelectric absorption result? When an x-ray photon interacts with an inner-shell electron.
PE. Incident photon ejects inner shell electron and is totally absorbed, what is the ejected electron called? photoelectron
What is the equation for PE? Ei= Eb+ Eke Ei= energy of incident photon, Eb= binding energy of electron, Eke= kinetic energy of photoelectron
PE. unstable ionized atom fills the vacancy of its shell where the photoelectron was, the energy released from the electron transfer is in the form of a _______, known as _______. characteristic photon, secondary radiation.
Radiation created at the x-ray target is considered what kind of radiation? primary
When characteristic radiation is produced in irradiated matter outside of the x-ray target it is termed what? Secondary radiation
What are the 3 basic rules that govern the possibility of a photoelectric interaction? *Incident x-ray photon energy greater than the be of the inner shell electron. *PE is more likely to occur when the x-ray photon energy and the electron binding energy are nearer to 1another (Ei and Eb are close). *e- is more tightly bound in its orbit.
First rule of a PE interaction? Incident x-ray photon energy must be greater than the binding energy of the inner-shell electron. (30keV photon cannot remove K-shell e- that has a binding energy of 33keV..)
2nd rule of a PE interaction? PE interaction is more likely to occur when the x-ray photon energy and the e- binding energy are nearer to one another. (a 40keV photon is more likely to interact by way of PE with a barium atom *k-shell Eb is 37.4 keV* than a 100 keV photon would)
..Along with 2nd rule of PE.. As photon energy/kVp increases, the chance of a photoelectric interaction ______. decreases.
3rd rule of a PE interaction? PE interaction more likely to occur w/ an e- that is more tightly bound in its orbit. -ex) K-shell BE for lead is 88keV, x-ray photons below 88 are incapable of removing 1 of those e-, but can be absorbed through PE interactions w/ L or M shell e-s.
Probability of a PE interaction _______ dramatically as the atomic number increases. increases. (bone has a Z# higher than soft tissue, so PE interactions are more likely to occur in bone than soft tissue and that is why x-rays are great for demonstrating bones)
PE = Subject contrast
10 keV or less results in what interaction Coherent scattering
Coherent scatter is AKA? Classical or unmodified (because nothing changes.. leaves w/same energy as entering and no ionizing of atom)
Two types of coherent scatter? Thomson and Rayleigh
Thomson scattering involves what? Rayleigh involves what? single electron of atom, rayleigh involves all the electrons of an atom
How does coherent scatter produce scatter? photon interacts & causes e-s of atom to vibrate at the SAME frequency as that incident e-. Vibrating/excited atom releases excess energy by producing secondary photon that has same energy & wavelength & frequency as incident but travels in diff direction
When does compton scatter occur? when an incident photon interacts with a loosely bound outer shell e- , removes it, and proceeds in a diff direction as a scattered photon.
Compton. The dislodged electron is called a ____ or _____ electron. compton or recoil electron
Compton. The original photon that exits the atom in a different direction is called what? Compton scattered photon
Unlike coherent scattering, the Compton scattered photon posses ____ energy than the incident photon and therefore has a ____ frequency and ____ wavelength. posses less energy, lower frequency and longer wavelength (because part of the energy of the incident photon was used/lost to dislodge the e-)
Equation of Compton effect? Ei= Es+ Eb + Eke Ei= energy of incident photon Es=energy of compton scat photon Eb= binding of compton electron Eke= kinetic energy given to the compton electron
Compton. The amount of energy retained by the scattered photon (original incident photon) is dependent on what two things? The initial energy of the photon, and its angle of deflection from the recoil electron (electron that was ejected)
Compton. At a deflection of 0 degrees what happens? As the angle of deflection increases to 180 what happens? 0= no energy is transferred because the photon is proceeding in its original direction. 180= more energy is transferred to the recoil e- so less energy remains with the scattered photon
Unwanted exposures caused predominantly by scattered photons and less commonly by secondary photons, are called what? Radiation fog
In a pair production interaction the energy of the x-ray photon is…. converted to matter in the form of two electrons.
For a pair production interaction to occur, a very high photon with energy of at least _____ MeV is required. 1.02 MeV
Pair production interaction. How is the pair of electrons created? Incident photon comes close to the nuclear field and loses all its energy, this energy is used to create the Negation and Positron.
Pair production. Annihilation reaction is what? Positron and electron combine, they disappear and give rise to two photons that move in opposite directions and each have energies of .51 MeV. (matter is being converted back to energy)
Photodisintigration requires energy above approximately what? 10 MeV
what is Photodisinigration interaction? High energy photon strikes the nucleus and all of its energy is absorbed by the nucleus.
In the diagnostic range, the majority of the x-ray beam is ______, and only a small percentage of photons exit to create the image. attenuated
As kVp increases, the total number of photons that are transmitted without interaction _____. increases.
As kVp increases, the total number of photons that are transmitted without interaction increases. This means that the probability of photoelectric and compton interactions ________ with increasing kVp. Decreases.
(PE vs Compton) % of photoelectric interactions _____ with increased kVp, % of compton interactions _____with increased kVp. Decreases, increases. ( there is an increased % of scatter and a decreased % of absorption of the attenuated beam)
Attenuation is the REDUCTION in the total number of photons REMAINING IN the BEAM after passing through material. (the thicker the body part, the greater the attenuation will be)
In the human body, what interaction is predominant through most of the diagnostic x-ray range? Compton scattering
In the human body diagnostic x--ray range, photoelectric interactions would predominate in what two circumstances? in lower energy ranges (25-45 keV produced by 40-70 kVp), and when high atomic number elements are introduced, such as contrast because they absorb a greater percentage of the photons.
when Photoelectric is more prevalent, image will possess ____ contrast. high contrast. Because incident photons are absorbed and aren't added fog. PE increases patient dose.
Low kVp/ high mAs or high kVp/low mAs. Which is better for pt? High kVp and low mAs is less pt dose.
Created by: Zoest35
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