Ch. 7 X-Ray Interactions with Matter

Question 1

classical interactions are also commonly known as what

Answer 1

coherent scattering or Thomson scattering

Question 2

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

Answer 2

classical interactions

Question 3

what energy levels does classical interactions take place in

Answer 3

low energy x-ray photons usually less than10 keV

Question 4

do classical interactions ionize the atom

Answer 4

No

Question 5

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

Answer 5

scatter photon

Question 6

what happens to most classical scatter photons

Answer 6

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

Question 7

how much energy does the reemitted classical photon have

Answer 7

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

Question 8

what energy levels does Compton scattering involve

Answer 8

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

Question 9

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

Answer 9

Compton scattering

Question 10

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

Answer 10

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

Question 11

what is the ejected electron in the Compton Scattering called

Answer 11

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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

Compton Interactions

Question 14

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

Answer 14

Compton Scatter

Question 15

What does Compton scattering depend on

Answer 15

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)

Question 16

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

Answer 16

no energy transfer

Question 17

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

Answer 17

max energy transfer and deflection

Question 18

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

Answer 18

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

Question 19

what is a major source of occupational exposre

Answer 19

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

Question 20

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

Answer 20

photoelectric interaction

Question 21

what is the resultant ejected electron called in the photoelectric interaction

Answer 21

photoelectron

Question 22

how much energy does the photoelectron leave with

Answer 22

incident photons energy minus the binding energy energy

Question 23

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

Answer 23

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

Question 24

what contributes significantly to patient dose

Answer 24

photoelectric interaction due to total absorption of the incident photon

Question 25

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

Answer 25

low energy Secondary photons which contribute primarily to patient dose

Question 26

what energy level does the photoelectric interaction usually take place in

Answer 26

throughout the diagnostic range, usually between 20-120 kVp

Question 27

what does a photoelectric interaction depend on

Answer 27

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

Question 28

the greatest number of photoelectric interactions occurs when

Answer 28

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

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

What are the two photon interactions not in the diagnostic realm

Answer 32

pair production and photodisintegration

Question 33

a positively charged electron

Answer 33

positron

Question 34

what is another name for electron

Answer 34

negatron

Question 35

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

Answer 35

0.51 MeV each

Question 36

what is the energy of an electron

Answer 36

0.51 MeV

Question 37

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

Answer 37

differential absorption

Question 38

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

Answer 38

transmission

Question 39

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

Answer 39

absorption

Question 40

body structures that readily absorb x-rays

Answer 40

radiopaque

Question 41

less dense structures that have a lower probability of absorption are

Answer 41

radiolucent

Question 42

where is radiation dose and damage more more apparent

Answer 42

macrolevel

Question 43

large molecules made up of thousands of atoms

Answer 43

macromolecules

Question 44

three most common effects of energy transfer in photon interactions

Answer 44

main-chain scission, cross-linking, point lesions

Question 45

most sensitive of moleucles

Answer 45

DNA

Question 46

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

Answer 46

radiolysis of water

Question 47

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

Answer 47

harmful free radicals

Question 48

positive contrast media is administered to increase what type of interactions

Answer 48

photoelectric