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Medical Radiation Sciences 1 > Unit 1 > Flashcards

Unit 1 Flashcards

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USMLE® Step 1 flashcards
1
Q

What is a radiograph?

A

an image generated through the use of X-rays

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2
Q

What is required to make a radiograph?

A

X-rays, object and recording device

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3
Q

What colours are what on a radiograph?

A

Bones are white, soft tissue is gray and everything else is black

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4
Q

What does kVp stand for?

A

kilovolts peak

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5
Q

Why can x-rays be dangerous?

A

they are a form of ionizing radiation

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6
Q

What is the correlation between kVp and contrast?

A

Higher kVp lowers contrast (chest) lower kVp increases contrast (abdomen)W

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7
Q

What factors affect attenuation?

A

atomic number, density, thickness, and energy of the x-ray photons

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8
Q

What is an IR?

A

Image receptor, the device that resolves the image

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9
Q

What is isotropic emission?

A

Release of beams equally in all directions

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10
Q

How do we reduce the effects of beam geometry?

A

smaller source, collimation and less OID (object to image receptor distance) - less space for electrons to diverge

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11
Q

What is the relationship between intensity and distance?

A

Intensity=1/distance^2

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12
Q

What is the charge of an electron?

A

-1.6x10^-19 coulombs

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13
Q

How many electrons in a coulomb?

A

6.24x10^18

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14
Q

What is the charge of a proton?

A

1.6x10^-19 coulombs

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15
Q

What are the 4 laws of electrostatics?

A
  1. opposites attract, likes repel
  2. charge is usually distributed evenly around objects
  3. charges concentrate around sharp corners
  4. coulomb’s law
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16
Q

What is the formula for Coulomb’s law?

A

F=k(q1q2/d^2)

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17
Q

What Is the q in coulombs law?

A

charge in Coulombs

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18
Q

What is the d in coulombs law?

A

distance in meters

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19
Q

What would happen to the electrostatic force between the cathode and the anode if we increased the distance between them by a factor of 5?

A

the force would be reduced by a factor of 25

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20
Q

What is electrical potential?

A

work required to move a positive charge from infinity to its current position, measured in volts (J/C)

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21
Q

What is potential difference?

A

how much energy is transferred moving a charge from one point to another, the negative point isn’t necessarily negative it is just the smaller of the 2 charges

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22
Q

What is electrodynamics?

A

the study of charges in motion

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23
Q

What is a conventional current?

A

what way the +ve charge WOULD move

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24
Q

What is electron current?

A

What way the -ve charge DOES move

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25
Q

What is an ampere?

A

it is a rate, and the unit for currents (C/s)

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26
Q

what is mAs?

A

total amount of charge
(C/s) x s = C

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27
Q

What is the relationship between current and potential difference?

A

Need potential difference for current to flow, however potential difference can exist without current

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28
Q

What is the potential difference in the X-ray tube?

A

the kVp - energy of electrons (eV)

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29
Q

What is mA in the tube?

A

the rate at which charge is flowing across the tube

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30
Q

What is mAs in the tube?

A

the total amount of charge flowing across the tube

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31
Q

What is the difference between direct an alternating current?

A

direct is unidirectional while alternating switches direction

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32
Q

What kind of current do we have running across the X-ray tube during an exposure?

A

Direct current

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33
Q

Why can’t you give an average of an alternating current?

A

peak symmetry

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34
Q

How do you find the Effective (RMS) of an AC?

A

Effective (RMS) = Peak/1.414 OR Peak x 0.707

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35
Q

What is the effective value?

A

The value of a constant DC that would generate the same amount of heat

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36
Q

What does RMS stand for?

A

Root mean squared

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37
Q

What are conductors?

A

Copper, Gold, Silver and Aluminum
- conduction band and valence band overlap

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38
Q

What are insulators?

A

No electron flow in conduction band
- oil, glass, rubber, plastic and ceramics

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39
Q

What are semi-conductors?

A
  • they have small intrinsic currents
  • can be doped into conductors
  • silicon and germanium
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40
Q

What is resistance?

A

impedes the current: caused by interactions of current electrons with the conductor or impurities
Unit: ohm - 1 ohm produced when 1V pushes 1A through a resistor

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41
Q

How do we see energy lost due to resistance?

A

Heat - work must be done to overcome the resistance

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42
Q

What are the factors that affect resistance?

A

Material, Area, Length and temperature

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43
Q

How does Area affect resistance?

A

more space to move through less resistance
- inversely proportional
2xArea = 1/2 resistance

44
Q

How does Length affect resistance?

A

more atoms to pass by, more resistance
- directly proportional
2xLength = 2xResistance

45
Q

How does temperature affect resistance?

A

Affects materials differently
- Increased T of conductor = resistance goes up
- Increased T of insulator/semi-conductor = resistance goes down

46
Q

What is Ohm’s Law?

A

The current flowing through a conductor is directly proportional to the potential difference between its ends, so long as all physical conditions remain constant

I=V/R

47
Q

What do the V I and R stand for in Ohm’s Law?

A

V is voltage measured in Volts
I is current measured in Amps
R is resistance in Ohms

48
Q

What is a series circuit?

A

one current path
CURRENT REMAINS THE SAME
voltage drops across each resistance
Rt = R1 + R2 + R3
It = I1 = I2 = I3
Vt = V1 + V2 + V3

49
Q

What is a parallel circuit?

A

VOLTAGE REMAINS THE SAME
Highest I through the lowest R
1/Rt = 1/R1 + 1/R2 + 1/R3
It = I1 + I2 + I3
Vt = V1 = V2 = V3

50
Q

What is a GFCI?

A

a ground fault circuit interrupter
- super sensitive detection of faults in outlets
- must be reset

51
Q

What is power?

A

the rate at which work is done
Unit: Watt (W) - Joules per second
V=P/I
P=I^2R
P=V^2/R

52
Q

How does a capacitor work?

A

similar to a battery
the potential difference decreases as the capacitor charges
- charging stops when there is no more potential difference
- used in timer circuits, electrical storage and waveform smoothing

53
Q

What are magnetic dipoles?

A

charges in motion creating magnetism, the direction of the motion affects the direction of the dipole

54
Q

What is a magnetic field?

A

perpendicular to the motion of charged particles

55
Q

What are lines of force?

A

amount of lines of force is Flux (Wb)

56
Q

What is flux density?

A

concentration of lines per area (T)

57
Q

What is a magnetic domain?

A

several aligned dipoles - happens spontaneously in some materials

58
Q

What are diamagnetic materials?

A

no inherent dipoles
slightly repelled by magnets
water, wood, plastic

59
Q

What are paramagnetic materials?

A

some inherent dipoles
can be weakly magnetized by an external magnetic field
gadolinium

60
Q

What are ferromagnetic materials?

A

contain many inherent dipoles
can become strong magnets
iron, cobalt

61
Q

What are the ways to create a magnet?

A

Interact with a magnet
hammer
run current through (right hand)

62
Q

What are permanent magnets?

A

hard ferromagnetic material
aligned domains stay aligned

63
Q

How do you destroy magnetism?

A

heat
hammer
reversing the field (left hand)

64
Q

What are temporary magnets?

A

soft ferromagnetic material
only stay aligned in magnetic field
electromagnets

65
Q

What is electromagnetism?

A

creating magnetism from electricity
running a current through a wire
can be turned on and off

66
Q

What type of magnetic force in straight wires?

A

weak

67
Q

Why do you want coiled wire in electromagnetism?

A

lines of force add together
increased flux density

68
Q

What factors affect magnetic field strength?

A

number of turns in coil
size of current
size of iron core

69
Q

What are the uses of electromagnetism?

A

electromagnetic locks
transformers
circuit breakers
motors

70
Q

What kind of current is used to create movement for the motor principle?

A

alternating

71
Q

What magnets does the motor principle use?

A

1 permanent and 1 temporary

72
Q

What is the conversion of energy in electromagnetism?

A

electrical energy - magnetic energy - kinetic energy

73
Q

What is electromagnetic induction?

A

using magnetism to create electricity, opposite of electromagnetism
- basis of power generation
- uses a permanent magnet, conductor and movement
- the conductor must cross magnetic lines of force for a charge to occur

74
Q

What is the conversion of energy in electromagnetic induction?

A

kinetic energy - magnetic energy - kinetic energy

75
Q

How is electromagnetic induction force created through movement?

A

when moving parallel to lines creates 0V, pea voltage when crossing at 90 degrees

76
Q

What are the factors that can affect induced voltage?

A
  • permanent magnet strength
  • armature: # of loops in coil and size of iron core
  • speed of movement
  • angle armature crosses lines of force
77
Q

What are the uses of electromagnetic induction?

A

transformers, induction motors and generators

78
Q

What is a transformer?

A

electromagnetism in the primary wire (pulsating DC OR AC) creates electromagnetic induction in the secondary wire
- both wires have the same amount of volts per turn

79
Q

What is the turns ration and transformer law?

A

Transformers can increase or decrease their voltage in their secondary wire
- turns ratio: Ns/Np
Pp=Ps
Ratio >1 = step-up - V increase I decrease
Ratio <1 = step-down V decrease I increase

80
Q

What is the transformer law?

A

Vp/Np = Vs/Ns
Vs/Vp = Ns/Np
Is/Ip = Np/Ns

81
Q

What is lamination in transformers?

A

layered, not a solid core
- increases efficiency

82
Q

What is an autotransformer?

A

smaller steps up or down
- this is why you have to choose mA in steps on X-ray machine

83
Q

What is a generator?

A
  • supply the energy used to create X-rays
  • different generators create different shaped waveforms
  • different generators produce x-ray beams of different intensities
84
Q

What is the issue with AC in X-ray?

A

generators create AC, but the charge is only effective at creating X-rays through half of the cycle, so wasting half the cycle

85
Q

What is self-rectification?

A

occurs with no rectifiers in place
- current can only run in one direction creating a HALF WAVE
exposures take 2x as long

86
Q

What are rectifiers?

A

the convert AC current to DC
- use 4-6 in X-ray circuitry

87
Q

what is generator rating?

A

Generator rating (kW) = kVp x mA / 1000
kVp will always be 100 kV if not given
- this measures maximum power of the generator
- usually use the max mA a generator can support at 100kVp for 100ms

87
Q

How are generators classified?

A

based on waveform and rating

88
Q

What is a single-phase generator?

A

-1 armature (coil) rotating within magnetic field
- electromagnetic induction creates voltage: usually AC
- 60Hz frequency

89
Q

What is a 3 phase generator?

A
  • rotate 3 armature in a magnetic field or rotate magnet surrounded by 3 coils
  • induction occurs in all 3, creating 3 separate waveforms
  • each are 60 Hz, but 120 degrees out of phase with each other
90
Q

Why are circuits kept separate until after rectification?

A

do not want them to summate
- 6 rectifiers for 3-phase, 6 pulse: 2 forward bias, 4 reverse bias

91
Q

What is a delta connection?

A

each coil end connected to each other in a triangle
- can provide high power and torque
- more prone to distortion and overheating

92
Q

What is the star connection?

A

each coil is connected to a common neutral wire and each other, like spokes on a wheel
- less power and torque
- less distortion and overheating

93
Q

Types of 3 phase generators?

A

6 pulse and 12 pulse
12 pulse uses more rectifiers

94
Q

What are high frequency generators?

A

can be single or 3 phase
0.5-25 kHz
Benefits: small size, very efficient, better beam quality, higher tube ratings

95
Q

What are the 7 steps of high frequency from source to tube?

A
  1. rectification
  2. smoothing
  3. inverter
  4. high tension transformer
  5. rectification
  6. smoothing
  7. create a radiograph
96
Q

What happens in the first rectification?

A

change 60 Hx AC to DC

97
Q

what happens first smoothing?

A

provide constant voltage
usually through capacitors - sometimes batteries

98
Q

inverter?

A

rapidly switches polarity of voltage
from DC back to AC - high frequency

99
Q

High Tension transformer?

A

large steppe transformer
V to kV
high voltage and high frequency

100
Q

2nd rectification?

A

change AC kV to DC kV

101
Q

2nd smoothing?

A

High frequency DC kV to constant kV

102
Q

More efficient generators have what kind of ripples?

A

lower

103
Q

What is a falling load generator?

A

uses shortest exposure time possible without damaging the tube
can cause focal spot blooming

104
Q

when is capacitor discharge used?

A

charge capacitors prior to leaving for portable X-rays
discharge during exposure

105
Q

What is a modular generator?

A

one transformer/generator supplies to 2-3 rooms

Medical Radiation Sciences 1 (4 decks)

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