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22 spring: Radiology > Test 1: Lecture 1 and 2 > Flashcards

Test 1: Lecture 1 and 2 Flashcards

1
Q

Xrays have short or long wavelength?

A

short
high energy
high radiation

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2
Q

the shorter the wavelength, the ___ the energy

A

higher

example: xrays short wavelength but high energy

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3
Q

X-rays are able to penetrate materials that ___ visible light

A

absorb or reflect

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4
Q

Xrays can produce ___and cause biological changes in tissue

A

ions

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5
Q

•X-rays are produced through conversion of ___ of accelerated electrons into ___

A

kinetic energy

electromagnetic radiation/energy

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6
Q

•Production, acceleration and deceleration of electrons takes place within the ___

A

X-ray tube

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7
Q

cathode

A

filament with negative charge

heating it results in electrons coming off and moving toward + anode which in turn reflects into Xrays

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8
Q

negative filament inside the Xray machine

A

cathode

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9
Q

what is the positive part of the Xray machine

A

anode

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10
Q

source of electrons in the xray machine

A

cathode

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11
Q

acceleration of electrons inside the xray machine is by

A

potential difference between +(anode) and - (cathode)

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12
Q

deceleration of electrons and conversion into Xrays is at the __

A

anode (+)

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13
Q

of the energy converted from kinetic energy into electromagnetic radiation what % are xrays?

A

less the 1%

99% is lost as heat

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14
Q

•Radiation emitted from the anode mostly by an interaction called ___(braking radiation)

A

Bremsstrahlung

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15
Q

nucleus has what charge and is made of ___

A

protons and neutrons

positive charge

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16
Q

electrons have __ charge

A

negative

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17
Q

outer shell electrons have __ energy then inner shell electrons

A

less

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18
Q

Bremsstrahlung

A

electron is deflected off course as it nears the nucleus, loss of energy is emitted as xrays

the closer to the nucleus the incident electron to the nucleus, the higher the energy of the emitted xray photon

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19
Q

___ is when electron is deflected off course as it nears the nucleus. Loss of energy is emitted as X-rays

A

bremsstrahlung/ braking radiation

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20
Q

label

A

cathode= negative filament

anode= positive

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21
Q

cathode is made of ___

A

tungsten filament that is heated and releases electrons

2 types of filaments (small and long)

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22
Q

mA

A

number of electrons flowing per second from the cathode to the anode

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23
Q

mAs

A

mA x exposure time= number of electrons flowing during the total exposure time from cathode to anode

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24
Q

how to get mAs

A

mA x exposure time

can get the same number with different mA or exposure times

want to use the smallest exposure time possible to reduce artifact from patient moving

500 mA x 0.02 seconds= 10 mAs

10 mA x 1 second= 10 mAs

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25
Q

what happens when you increase mAs

A

increases filament heating and tube current will increase number of electrons moving from cathode to anode= increase number of xrays made

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26
Q

changing mA will do what to the energy of the xrays made

A

max energy will be the same for different mA

xrays with higher mA will have more electrons or more xrays

increase quantity of xray, not quality of xray

(not stronger (not more penetrating), just more)

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27
Q

kVp

A

kilovolt peak

voltage difference between anode and cathode

high potential difference leads to acceleration of the electrons in a vacuum towards the anode

the bigger the kVp, the stronger/more penetrating the xray

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28
Q

what does it mean if 55 kVp on the control panel?

A

Maximum kinetic energy of the electrons: 55 keV (energy from traveling form cathode to anode)

Maximum photon energy: 55 keV (can not be bigger then the max kinetic energy

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29
Q

increasing kVp will do what?

A

will increase the energy/penetrating power of the xray produced

(peak energy and average energy will increase)

will also increase the number of electrons/xrays produced

increases quality and quantity of xray

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30
Q

change in ___ will increase the number of xrays as well as the penetrating power of the xray

A

kVp

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31
Q

why use tungsten for anode

A
  • High atomic number (high conversion efficiency from electrons to X-rays)
  • High melting point
  • Relatively resistant to surface damage

prevents overheating by spinning

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32
Q

which filament size is good for fine detail

A

small

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33
Q

which filament size is good for high heat?

A

large

reduced detain but can use higher exposures

(large electron beam)

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34
Q

collimation

A

making xray beam smaller to decrease unnecessary exposure and improve picture

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35
Q

what does it mean when xray beam is polychromatic

A

has wide range of low to high power xrays

low xrays are not strong enough to get through patient and causes scatter and increases the dose of radiation to the patient

we use filters to reduce low energy xrays

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36
Q

filtration of xray is meant to ___

A

decrease low energy xrays

low energy not strong enough to make xray, just contributing to radiation

37
Q

glass envelope around the xray tube is a form of ___

A

inherent filtration

38
Q

what are some examples of inherent filtration

A

glass envelope, insulating oil, plastic tube window

39
Q

what is an example of added filtration

A

aluminium (1.5-2 mm)

absorbs low energy xrays

40
Q

Attenuation of the beam by the different tissues of the patient reduces its intensity and creates the image: ___

A

‘shadowgram’

41
Q

film not exposed to xray are ___

A

white or light

(xrays where absorbed by material and did not make it to the table)

42
Q

___ is decrease in intensity of an xray beam as it passes through matter

A

attenuation

43
Q

___ is photon removed from a beam

A

absorption

44
Q

___ is when a photon changes direction

A

scatter

45
Q

two types of attenuation

A

absorption and scatter

46
Q

___ is xray passes through matter without interaction

A

transmission

47
Q

photoelectric effect

A

complete absorption of xray photon

xray photon hits inner shell electron, this becomes ionized. not strong enough to leave and gets absorbed

outer shell electron fills empty inner shell space→ create a low energy xray (characteristic radiation)

photoelectron and characteristic radiation: both absorbed, not strong enough to get out of cell

48
Q

what effect is compete absorption?

A

photoelectric effect

photoelectron and characteristic radiation: both absorbed, not strong enough to get out of cell

49
Q

photoelectric effect causes the atom to become ___

A

ionized

(loses an electron- this is where things go wrong and cause cancer from radiation)

50
Q

what is the probability of the photoelectric effect

A

xray totally absorbed

Probability of occurrence: Z3/E3

Proportional to atomic number cubed (Z3)

Inversely proportional to X-ray energy cubed (E3)

In summary: PE reactions are most likely to occur with low energy photons and elements with high atomic numbers

51
Q

when is PE more likely to occur?

A

Photoelectric effect (total absorption) reactions are most likely to occur with low energy photons** and elements with **high atomic numbers

52
Q

___ magnifies differences in tissues composed of different elements such as bone and soft tissue (large difference in atomic number) – good contrast!

A

photoelectric effect

53
Q

compton effect

A

scatter effect

  • Incoming photon ejects free outer shell electron from the tissue atom. The photon is scattered
  • The scattered photon has lower energy, but may produce more ionizations, fog the film and is a radiation safety hazard
  • The ejected orbital electron is absorbed in the patient
54
Q

in the ___ effect, photon will hit outer shell electron

A

compton/ scatter

55
Q

what can happen to the scattered photon

A

ionize other atoms, create fog on the film and can exposure holder to radiation

56
Q

what is the probability of compton effect

A

Increases with electron density, which depends on the tissue density and not the atomic number

Relative proportion of Compton vs PE interaction increases in favor of COMPTON as energy of X-ray beam increases

Compton Effect causes almost all of scatter reaching film

57
Q

as energy increases what effect also increases in probability

A

compton / scatter

58
Q

increases in ___ will increase the probability of the compton effect

A

electron density (tissue density)

59
Q

which of kVp or mAs controls the energy of the xray beam produced in the tube?

A

kVp

higher kVp = more compton effect, less photoelectric

60
Q

which one has more kVp

A

more kVp= more energy= more compton effect

61
Q

•___increases with high atomic number materials and low energy X-rays: GIVES CONTRAST

A

Photoelectric Effect

62
Q

___ increases with higher density tissues and high energy X-rays: REDUCES IMAGE QUALITY (DECREASES CONTRAST) AND EXPOSES PEOPLE AROUND PATIENT TO SCATTERED RADIATION!

A

•Compton Scatter

63
Q

degree of xray attenuation is based on

A
  • Effective atomic number (Z) of each tissue (higher Z = more PE effect)
  • Density or specific gravity of tissue (higher density = more compton)
  • Thickness of tissue
  • Photon energy - kVp (higher kVp= more compton)
64
Q

why is water and muscle a similar color on the xray

A

similar density and atomic number (Z)

65
Q

what are the 5 basic radiopactities

A
66
Q

___ radiation from sources other than the primary x-ray beam

A

scatter radiation

safety hazard

produces reduced detail and film fog

67
Q

factors that influence the amount of scatter

A

tissue thickness

field size

kVp (higher = more energy= more scatter)

68
Q

how to reduce scatter

A

collimation

low kVp

69
Q

how to reduce the effect of scatter

A

grids (alternating lead and aluminum strips

used for tissue thickness greater than 10-12 cm

some primary beams absorbed → must increase mAs

70
Q

the goal of ___ is to obtain maximal diagnostic information with minimal exposure of the patient, radiology personnel and the general public

A

radiation protection

71
Q

ALARA

A

as low as reasonably achievable

use smallest exposure possible

72
Q

damage to tissue from xrays is from:

A
  • Direct interaction with DNA
  • Indirect effect: ionization of water molecules leads to formation of free radicals, which can then alter cellular mechanisms directly or via damage to genetic material
73
Q

what are the three most sensitive tissue to xrays?

A
  • Actively dividing tissues such as bone marrow and epithelial cells of the gastrointestinal tract are more responsive to radiation.
  • Gonadal cells: damage can be amplified (genetic damage)
  • Fetal cells: the younger the fetus the greater the potential for damage (death, congenital malformations, growth defect)
74
Q

stochastic effects

A

•NO threshold dose, BUT probability of damage increases with dose (cancer, genetic effects)

can happen 1st xray or 100th xray

main concern!

75
Q

what is the main concern of xray radiation

A

stochastic effect

•NO threshold dose, BUT probability of damage increases with dose (cancer, genetic effects)

76
Q

deterministic effect

A
  • High radiation exposure
  • Clinical signs appear after a threshold dose
  • Severity increases with the dose (erythema, ulcerations, hematopoietic damage, cataract…)
  • Mainly seen in radiation therapy and nuclear accidents
77
Q

___ effect is seen after a threshold dose

A

deterministic

mainly seen in radiation therapy and nuclear accidents

78
Q

methods of xray protection

A
  • Indication! Is there a need for these radiographs?
  • Good radiographic technique

•Time

•Sedation / anesthesia

•Distance: inverse square law

•Filtration

•Shielding

  • Reduction of scatter: collimation!
  • Personnel monitoring
79
Q

inverse square law

A

•If the distance from the primary source is doubled, the intensity will decrease by a factor of four

80
Q

true or false

protection such as shield works for direct radiation

A

false

protection only helps with reduction of scatter radiation

81
Q

how to measure radiation exposure

A

dosimeter

82
Q

amount of radiation allowed per year

A
  • Whole body: 50 mSv (milli-Sievert) / YEAR
  • Embryo/Fetus of a WORKER: 5 mSv over 9 months
83
Q

natural background exposure in the US

A

3 mSv/year

84
Q

The main type of interaction producing X‐rays in the tube is:

Heat production

Bremmstrahlung

Photoelectric effect

Reflection radiation

Acceleration radiation

A

bremmstrahlung

85
Q

Compared to a 90 kVp setting, a 70 kVp setting (keeping mAs the same)…

A

Decreases intensity, peak energy and average energy of the X‐ray beam

86
Q

What are the two main types of interaction of X‐rays with matter?

A

Photoelectric and Compton effect

87
Q

You are standing 1 m away from the patient while someone is taking a radiograph. If you were standing 2 m away, your exposure to scatter radiations would be:

A

Divided by 4

88
Q

The additional filtration at the outlet of the X‐ray tube:

A

Eliminates low energy photons that would increase exposure and not contribute to the image

22 spring: Radiology (11 decks)

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