Unit 2: Interaction with Matter

Question 1

What are the five types of interactions with matter?

Answer 1

coherent scatter
compton scatter
photoelectric effect
pair production
photodisintegration

Question 2

Coherent scatter can also be called:

Answer 2

Thompson scatter or Unmodified scatter

Question 3

describe Coherent scatter:

Answer 3

Interaction between the incident x-ray and a target atom that becomes excited. The atom releases this excess energy as a scattered x-ray photon that changes in direction

no energy transfer and no ionization occur

Question 4

What scatter is of little importance to diagnostic radiology?

Answer 4

coherent scatter

Question 5

describe Compton scatter:

Answer 5

interaction between incident x-rays and outer-shell electrons and ejects electron and ionizes atom

photon changes direction with a reduction in its energy

Question 6

What is the ejected electron called?

Answer 6

Compton/recoil electron

Question 7

In the energy transfer of Compton scatter, what retains most of the energy?

Answer 7

the scattered x-ray

Question 8

define absorbed dose:

Answer 8

amount of energy that ionizing radiation gives to a given mass of matter (radiation absorbed by an object)

Question 9

What are the three types of Compton scatter?

Answer 9

back
side
forward

Question 10

describe back scatter:

Answer 10

photon scattered 180° perp. to beam, strikes the IR/pt and travels back toward the tube

Question 11

What causes back scatter?

Answer 11

photon strikes an outer shell electron with a head on collision

Question 12

Back scatter can contribute to:

Answer 12

additional patient dose

Question 13

describe side scatter:

Answer 13

photon scatters straight off to the side

Question 14

What causes side scatter?

Answer 14

photon strikes an outer shell electron on its outer edge

Question 15

What is side scatter the main source of?

Answer 15

occupational dose in radiography and fluoro

Question 16

describe forward scatter:

Answer 16

photon travels in a forward direction and strikes the IR

provides no diagnostic information (no anatomy represented)

Question 17

What causes forward scatter?

Answer 17

photon grazes an orbital electron by hitting side of atom and changes in a different forward direction

barely gives up any of its energy

Question 18

What is the type of scatter that reduces image contrast/noise?

Answer 18

forward

Question 19

List the factors that affect production of Compton scatter radiation:

Answer 19

field size (collimation)
body part thickness
body part density
body part electron density
photon energy
?kVp

Question 20

What is the relationship between Compton scatter and field size?

Answer 20

larger field size = more Compton scatter (more noise and lower image contrast)

Question 21

what is the most effective way of reducing pt dose?

Answer 21

collimation

Question 22

What is the relationship between Compton scatter and body part thickness?

Answer 22

thicker part = more Compton scatter

compress thicker body parts

Question 23

What is the relationship between Compton scatter and body part density?

Answer 23

greater the density = greater the Compton scatter production

Question 24

T/F: atomic number of tissue does not effect the likelihood of Compton scatter.

Answer 24

true

Question 25

Why do more denser parts increase scatter?

Answer 25

atoms are packed more tightly, meaning more electrons leading to increase in scatter

Question 26

The greater amount of water present in tissue will produce a _________ amount of Compton.

Answer 26

greater

Question 27

What is the relationship between Compton scatter and kVp?

Answer 27

increasing kVp will increase Compton scatter

Question 28

Why do we use grids?

Answer 28

higher body parts require higher kVp settings, which will produce more scatter

Question 29

What do grids do?

Answer 29

clean up forward Compton scatter

Question 30

list the ways to reduce Compton scatter lowering image contrast:

Answer 30

lowest possible kVp grids smaller field size air gap technique compression

Question 31

describe the Photoelectric effect:

Answer 31

x-rays undergo ionizing interactions with inner-shell electrons that become totally absorbed by the K-shell electron pt dose and absorption

Question 32

Photoelectric interaction produce secondary radiation through what?

Answer 32

cascading effect

Question 33

What must happen in order for the photoelectric interaction to happen?

Answer 33

incident x-ray energy must be equal to or slightly greater than the electron binding energy

Question 34

What are the factors that affect photoelectric effect?

Answer 34

kVp body part thickness body part density atomic number tissue

Question 35

What is the relationship between the photoelectric effect and kVp?

Answer 35

increasing kVp -> increases photoelectric interaction due to increase in quantity

Question 36

increasing kVp will:

Answer 36

decrease diff. absorption

Question 37

What is the relationship between the photoelectric effect and body part thickness and density?

Answer 37

thicker and denser body parts -> increases chances of photoelectric interactions

Question 38

What is the relationship between the photoelectric effect and the atomic number of tissue?

Answer 38

atomic number increases -> photoelectric effect increases greatly

Question 39

increasing x-ray beam energy will result in:

Answer 39

overall increase all interactions fewer avg. Compton interactions much fewer avg. photoelectric interactions more transmission through pt

Question 40

describe pair production:

Answer 40

photon escapes influence w/ orbital electrons and interacts w/ the nucleus

Question 41

what happens to the photon during pair production?

Answer 41

it disappears and is replaced with two electrons (positron and negatron)

Question 42

pair production requires a photon energy that is:

Answer 42

greater than 1.02 MeV

Question 43

describe photodisintegration:

Answer 43

photon escapes interaction w orbital electrons and becomes absorbed by nucleus

Question 44

What happens to the nucleus during photodisintegration?

Answer 44

nucleus enters an excited state and emits a nucleon or other nuclear fragment

Question 45

photodisintegration requires a photon energy that is:

Answer 45

10 MeV or greater