chapter 3 EXAM 2 Flashcards Preview

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Flashcards in chapter 3 EXAM 2 Deck (55):
1

milliampere seconds mAs

quantity
product of exposure time and tube current
a measure of the total number of electrons that travel from the cathode to the anode

2

peak kilovoltage kVp

quality
controls the quality or penetrating power of the photons in xray beam

3

when radiation interacts with matter (the body) some photons are....

some photons are absorbed
some are scattered and some pass through without interacting at all

4

absorption

transference of electromagnetic energy from an xray beam to the atoms or molecules of the matter through which it passes

5

scatter

a change in direction of travel of an xray photon that may also involve a potential loss of radiation energy

6

absorption + scatter =

attenuation

7

direct transmission

when photons pass through the patient without interacting and reach the IR

8

primary radiation

emerging xray photon beam

9

indirect transmission

primary photons that undergo compton and or coherent interactions and are scattered or deflected after they go through an object

10

an optimal xray image is formed only when

direct transmission xrays reach the IR

11

a radiographic image is formed from

directly transmitted photons and indirectly transmitted (scattered) photons

12

attenuation

refers to any process decreasing the intensity of the primary photon beam

13

radiographic fog

undesirable additional density on a radiographic image caused by scatter reaching the IR

14

true or false
photon interaction is random

true

15

an xray image results from the difference between

the xrays absorbed photoelectrically by the patient and those transmitted to the IR

16

differential absorption

different degrees of absorption in different tissues that result in image contrast and formation of the image

17

what are the 4 factors that influence probability of interactions of photons

1. photon energy
2. atomic number
3. mass density
4. tissue thickness

18

as photon energy increases,

kvp increases and absorption is reduced

19

as atomic number increases,

it increases the chances that the xray photon will be absorbed to the 3rd power

20

as xray energy increases

fewer compton interactions
fewer photoelectric interactions
more passing through without interacting

21

as tissue atomic number increases

no change in compton interactions
more photoelectric interactions
less passing through without interacting

22

as tissue mass density increases

proportional increasie in compton interactions
proportional increase in photoelectric interactions
proportional reduction in passing through without interacting

23

5 types of interaction between x radiation and matter

1. coherent scattering
2. compton scattering
3. photoelectric absorption
4. pair production
5. photodisintegration

24

coherent scattering is also called

classic, elastic or unmodified scattering

25

coherent scattering

involves low energy photons below 10 KeV
when the low energy photon interacts with tissue, it does not loose energy. It just changes direction and becomes excited.
no ionization occurs here.

26

photoelectric absorption is the most important

mode of interaction between xray photons and the atoms of the pts. body for producing useful images

27

photoelectric absorption

interaction between the dray photon and an inner shell electron (k shell)

28

to dislodge an inner shell electron from its orbit, the xray photon must

be able to transfer a quantity of energy equal to or greater than the electron binding energy

29

on interacting with the inner shell electron, the xray photon surrenders

all of its energy to the orbital electron and ceases to exist
it gets absorbed

30

the ejected electron is called a

photoelectron

31

auger effect

process that can occur as a result of photoelectric interactions
occurs when an inner shell electron is removed from an atom causing an inner shell vacancy

32

what are the byproducts of photoelectric absorption

photoelectrons
characteristic xray photons

33

probability of occurrence of photoelectric absorption depends on

the energy of the xray photons and the atominc number of the atoms it interacts with

34

photoelectric absorption increases to the 3rd power dramatically as the

energy of the incident photon decreases.

35

the probability of photoelectric absorption increases dramatically when

the atomic number of the atoms increases

36

when mass density is doubled, the chance for xray interaction is doubled because

twice as many electrons are available for interaction

37

the interaction of xrays with tissues is proportional to the

mass density of the tissue

38

T or F
if 2 structures have the same mass density and atomic number, but one is twice as thick, the thicker structure will absorb twice as many photons

True

39

T or F
the less a given structure attenuates xrays, the darker its radiographic appearance

true

40

the greater the difference in the amount of photoelectric absorption, the greater the

contrast will be between adjacent structures of differing atomic numbers.

41

as absorption increases, so does

the patient dose :(

42

compton scattering is also called

incoherent scattering
inelastic scattering
modified scattering

43

what is compton scattering

the interaction of xrays with matter that is responsible for most of the scattered radiation produced during radiologic procedures

44

process of compton scattering

incoming photon interacts with loosely bound outer shell electron. it surrenders part of its energy to dislodge the electron ionizing the atom

45

the ejected electron in compton scattering is called

compton scattered electron
secondary electron
recoil electron

46

what can happen to the compton scattered photon

it can interact with other atoms
it may emerge from the pt. and reach the IR causing fog
it could emerge from the pt. and expose personnel

47

compton scattering is the source of

most of the occupational radiation exposure that radiographers receive

48

the probability of the compton scattering effect does not depend on

the atomic number of the atom
doesn't matter what it hits. it will effect an atom of soft tissue the same way as an atom of bone

49

compton scattering provides no useful info on the radiograph. it results in

reduced image contrast

50

Pair production does not occur unless

energy of the incoming xray photon is at least 1.022 mega electron volts
this is far above the energy used in diagnostic radiology

51

pair production process

incoming photon interacts with the nucleus of an atom of biologic tissue and disappears
in the process energy of the photon is transformed into 2 new particles

52

what are the 2 new particles the photon is transformed into in pair production

negatron (ordinary electron)
positron (positively charged electron)

53

annihilation event

the positron and the electron it interacted with are destroyed and their energy is converted into 2 xray photons that radiate out of the atom

54

photodisintegration

energy above 10 Megaelectron volts
energy too high for diagnostic radiation

55

process of photodisintegration

high energy photon collides with the nucleus of an atom and the nucleus emits a neutron
this makes the nucleus radioactive