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physics > Ch. 7 X-Ray Interactions with Matter > Flashcards

Ch. 7 X-Ray Interactions with Matter Flashcards

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1
Q

classical interactions are also commonly known as what

A

coherent scattering or Thomson scattering

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2
Q

incident photon interacts with an orbital electron of a tissue atom and the atom absorbs the energy and then releases it in a new direction

A

classical interactions

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3
Q

what energy levels does classical interactions take place in

A

low energy x-ray photons usually less than10 keV

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4
Q

do classical interactions ionize the atom

A

No

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5
Q

what is the released energy during the classical interaction called after it is reemitted in a new direction

A

scatter photon

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6
Q

what happens to most classical scatter photons

A

get absorbed in the body, adding slightly to patient dose not the image

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7
Q

how much energy does the reemitted classical photon have

A

same energy when the incident photon energy, just in a new direction

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8
Q

what energy levels does Compton scattering involve

A

moderate energy x-ray photons usually between 20-40 keV

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9
Q

incident photon interacts with an orbital electron of a tissue atom and removes it from its shell, incident photon loses up to 1/3 original energy and gets deflected in new direction

A

Compton scattering

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10
Q

In Compton interaction the incident photon can interact with one of the middle orbital electrons, knocking it out and then causing the cascade effect. What are the cascade released photons called

A

secondary photons - they are low energy photons contributing to patient dose

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11
Q

what is the ejected electron in the Compton Scattering called

A

Compton electron or secondary electron - enough energy to go on to interact with other atoms

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12
Q

what is the incident photon called after it is deflected in a new direction

A

Compton scatter photon - enough energy to interact with another atom or contribute to image receptor

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13
Q

what is the most prevalent/common interactions between x-ray photons and the human body

A

Compton Interactions

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14
Q

What is responsible for most of the scatter/fog on the image

A

Compton Scatter

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15
Q

What does Compton scattering depend on

A

Photons energy - more energy the less likely to interact and more likely it is to penetrate through the body, but more energy more common the chance of Compton interactions related to photoelectric interactions (with k-shell electron)

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16
Q

what does a deflection of 0 degrees in the Compton scattering indicate

A

no energy transfer

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17
Q

what does a deflection of a photon180 degrees indicate in a Compton scatter interaction

A

max energy transfer and deflection

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18
Q

how much energy does the scattered photon in a Compton scatter interaction usually keep

A

2/3 it’s original energy, only loses 1/3 energy

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19
Q

what is a major source of occupational exposre

A

Compton scatter photon - the incident photon that interacts and gets ejected in a new direction

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20
Q

this interaction involves inner-shell orbital electrons of the tissue atom; incident photon removes one of these inner-shell electrons from orbit, but expends all of it’s energy in doing so and gets totally absorbed

A

photoelectric interaction

21
Q

what is the resultant ejected electron called in the photoelectric interaction

A

photoelectron

22
Q

how much energy does the photoelectron leave with

A

incident photons energy minus the binding energy energy

23
Q

which photoelectron will have more energy, one coming from bone or from soft tissue

A

soft tissue because the binding energy of soft tissue is much less; both will still have enough energy to go on to interact on their own though

24
Q

what contributes significantly to patient dose

A

photoelectric interaction due to total absorption of the incident photon

25
Q

Photoelectric interactions also create a cascade event since the k-shell electron is being ejected; just like the Compton interaction, what does this cascade produce

A

low energy Secondary photons which contribute primarily to patient dose

26
Q

what energy level does the photoelectric interaction usually take place in

A

throughout the diagnostic range, usually between 20-120 kVp

27
Q

what does a photoelectric interaction depend on

A

energy of incident photon and the atomic number of the tissue atom it would interact with

28
Q

the greatest number of photoelectric interactions occurs when

A

incident photon energy is equal or only slightly greater than the binding energy of the inner-shell electron, as the incident photons energy increase, it’s chances of penetrating increase and therefore interaction decreases

29
Q

what is the relationship between photoelectric interaction and the incident x-rays energy

A

inverse cubic relationship - probability of photoelectric interaction is inverse to the 3rd power of the x-rays energy

30
Q

what is the relationship between photoelectric interaction and atomic number of atom being interacted with

A

direct cubic relationship - chance of photoelectric interaction is direct to the 3rd power of the atomic number of the absorbing material

31
Q

what is used to increase photoelectric effects in tissues with low atomic numbers

A

barium or iodine - have high atomic numbers to increase photoelectric events
Shielding is also used to increase photoelectric effects to reduce scatter

32
Q

What are the two photon interactions not in the diagnostic realm

A

pair production and photodisintegration

33
Q

a positively charged electron

A

positron

34
Q

what is another name for electron

A

negatron

35
Q

for each particle in a pair production interaction exist, how much energy must they have

A

0.51 MeV each

36
Q

what is the energy of an electron

A

0.51 MeV

37
Q

the difference between x-ray photons that are absorbed photoelectrically and those that penetrate the body

A

differential absorption

38
Q

x-rays photons that pass through the body and reach the image receptor

A

transmission

39
Q

photons that are attenuated by the body and do not reach the image receptor

A

absorption

40
Q

body structures that readily absorb x-rays

A

radiopaque

41
Q

less dense structures that have a lower probability of absorption are

A

radiolucent

42
Q

where is radiation dose and damage more more apparent

A

macrolevel

43
Q

large molecules made up of thousands of atoms

A

macromolecules

44
Q

three most common effects of energy transfer in photon interactions

A

main-chain scission, cross-linking, point lesions

45
Q

most sensitive of moleucles

A

DNA

46
Q

x-ray photons interacting with water molecules within the body; ionizes the water molecule, creating an ion pair - positive water molecule and negative free electron and both unstable and undergo interactions to regain stability

A

radiolysis of water

47
Q

radiolysis of water can create these which that can indirectly damage molecules and cells

A

harmful free radicals

48
Q

positive contrast media is administered to increase what type of interactions

A

photoelectric

physics (9 decks)

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