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Medical Radiation Sciences 1 > Unit 3 > Flashcards

Unit 3 Flashcards

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USMLE® Step 1 flashcards
1
Q

What is radiation?

A

the transmission of energy through waves or particles
can be ionizing or nonionizing

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2
Q

What are the 4 types of radiation?

A

Electromagnetic (EMR)
Particulate
Acoustic
Gravitational

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3
Q

What is electromagnetic radiation and how is it created?

A

charges have an electric field around them
moving charges create a magnetic field
disturbances in a charge create electromagnetic waves

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4
Q

How does electromagnetic radiation travel?

A

energy in a sinusoidal wave
the waves have no weight
EMR waves can interact with object as if they are particles

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5
Q

What is wave particle duality?

A

acts like a wave and a particle

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6
Q

What is the wave theory?

A

EMR affects both electrical and magnetic fields
fields are perpendicular to the direction of energy

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7
Q

What is amplitude?

A

maximum field strength
- higher amplitude = higher intensity

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8
Q

What is wavelength?

A

has the symbol lambda
distance between same points in the wave
- shorter wavelength = higher intensity

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9
Q

What is frequency?

A

cycles per second
measured in Hz
- higher frequency = higher intensity

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10
Q

what is a period?

A

how long each cycle takes
1/f

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11
Q

What is the formula for EMR waves in a vacuum?

A

c=f(lambda)

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12
Q

What is c?

A

the speed of light
c= 3 x 10^8 m/s

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13
Q

Memorize EMR spectrum

A

slide 11

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14
Q

What are the 4 types of wavelike interactions?

A

reflection
refraction
diffraction
interference

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15
Q

what is reflection?

A

bouncing off of an interface

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16
Q

what is refraction?

A

change in direction from change of speed

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17
Q

what is diffraction?

A

wave bounds around borders to create a pattern

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18
Q

what is interference?

A

waves can add together or cancel out

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19
Q

which wavelike interactions do x-rays do?

A

diffraction

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20
Q

what is quantum?

A

smallest unit of something

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21
Q

what is quantum of X-rays?

A

photons
we think of x-rays as distinct photons not as continuous waves
- particle like unit, but travels as a wave

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22
Q

Quantum theory equation?

A

each photon has a different amount of energy calculated by
E=hf
E = energy
f= frequency
h = Planck’s constant

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23
Q

What is ionization?

A

when radiation knocks e- of an atom making it a positive ion

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24
Q

what is excitation?

A

when an e- gains energy to go up a valance level

25
Q

what are the particle like interactions?

A

ionization
excitation
flourescence

26
Q

what is fluorescence?

A

immediate release of energy when electrons fill the lower shell again after an x-ray makes a space either by excitation or ionization

27
Q

What are the properties of a low energy EMR vs high energy EMR?

A

Lower energy EMR tends to have more wave-like properties
Higher energy EMR tends to have more particle like properties

28
Q

In the x-ray beam are the wavelengths of photons uniform?

A

no, beam is comprised ion many different wavelengths

29
Q

The majority of the x-ray beam are _________ energy photons?

A

low

30
Q

Max energy of a photon is determined by?

A

kVp

31
Q

All photons have the same?

A

speed

32
Q

For heat generation, where do most interactions occur?

A

between tube current electrons and outer shell electrons of Tungsten

33
Q

What type of radiation is released in heat generation in the tube?

A

Infrared

34
Q

What is the relationship between atomic number and binding energies?

A

proportional

35
Q

Shells and binding energies of Tungsten?

A

Shell - # e- - Binding E (keV)
K - 2 - 69
L - 8 - 12
M - 18 - 3
N - 32 - 1
O - 12 - 0.1
P - 2 - negligible

36
Q

What is characteristic radiation?

A

the ionization of Tungsten
Flourescence release the characteristic radiation - specifically talking about the K shell when talking about X-rays
This creates 0-10% of beam intensity

37
Q

What is the Characteristic energy and how is it calculated? What is the characteristic energy of P to K of Tungsten?

A

difference in binding energies
69 - negligle = 69 keV

38
Q

How much energy must an electron have to dislodge a tungsten electron?

A

at least 69.5 keV
under this would mean 0% of beam is characteristic (useful) radiation

39
Q

Line graphs

A

also referred to as: discrete spectrum, line spectrum, homogenous spectrum, mono energetic spectrum
characteristic radiation only exits at certain levels
graphs show lines at each energy level

40
Q

what kVp gives unto 10% useful radiation?

A

70 - 150 kVp

41
Q

What does Bremen mean?

A

to brake/decelerate

42
Q

What does Strahlung mean?

A

radiation

43
Q

what is Bremsstrahlung radiation?

A

deceleration of electrons releases X-rays

44
Q

How does Bremsstrahlung radiation occur?

A

electrons pass by positively charged nucleus and changes trajectory and slows down.

45
Q

How do you create a max E photon Bremsstrahlung radiation?

A

needs to collide with nucleus and lose all kE in one go and all E become Xray photons
- rare interaction

46
Q

Tungsten with Bremsstrahlung

A

high z
- very positive nucleus
attracts and slows electrons more
- increase KE lost
- increased E of photons

47
Q

What are the different photon energies in a Bremsstrahlung beam?

A

Heterogenous
Continuous
Polyenergetic

48
Q

where do most of the X-ray photons come from on the X-ray curve?

A

1/3 to 1/2 - more lower E photons

49
Q

How is the intensity of the the beam calculated?

A

intensity = Energy/area/time
it is the area under the curve/line of the graph

50
Q

What is intensity of the beam affected by?

A

energy of photons (quality)
photons per second (quantity)

51
Q

what affects the quality of the characteristic radiation?

A

characteristic radiation only exists at set values
changing z changes energy levels
- the only thing that changes the energy of the photons is the element that they are made from via atomic number

52
Q

what changes the quantity of characteristic radiation intensity?

A

increased kVp: increases amount of energy available to create photons
decreased ripple: more electrons have peak energy to make more photons
increased mA: more electrons to make photons
increased z: depends on k-shell binding energy kVp

53
Q

what changes the quality of Bremsstrahlung radiation intensity?

A

increased kVp: increases peak energy of photons - increases average energy
decreased ripple: more electrons have peak energy and more E lost (good thing)
increased z: increases deceleration of electrons (good thing)

54
Q

what is max energy?

A

highest energy photons possible
Depends on kVp
as far right as the Xray curve goes

55
Q

What is low energy?

A

lowest energy photons
filtration
mostly Bremsstrahlung radiation
most likely to be filtered out - more filtration = less photons
L characteristic radiation would be low energy as well

56
Q

average beam energy

A

effective beam energy
- affected by waveform, filtration, z
1/3 to 1/2 of peak
for average kVp multiply by 1/3 if crappy generator
1/2 is a better generator

57
Q

line spectra

A

constant (distinct) energy levels
determined by z
height might change but not spot because it is fixed due to atomic number

58
Q

study the emission spectra graphs

A

Slides 63-67

Medical Radiation Sciences 1 (4 decks)

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