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Radiology > Physics of Radiology > Flashcards

Physics of Radiology Flashcards

1
Q

Atomic structure

Atomic number

Atomic Mass

A
  • Nucleus consists
    • Z atomic number
      • number of protons
      • Determines identity of element
    • A Atomic Mass
      • Number of protons and neutrons
      • Determines stability of element
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2
Q

Relation of size of atom, number of protons and neutrons and stability

A
  • Neutrons =Protons Stable
  • More neutrons larger atom, less protons= Unstable
    • Larger atom= more neutrons= unstable
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3
Q

Ionization

A
  • A neutral atom loses an electron
  • Ion pair is formed
    • Positive atom and negative free electron
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4
Q

Electron Binding energy

A
  • Energy that an atom holds onto an electron
  • Larger atoms have higher binding energies
  • Closer orbital shells have higher binding energies
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5
Q

Cathode and anode charges

A
  • Cathode Negative
  • Anode Positive
  • High voltage between cathode and anode
    *
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6
Q

Where are electrons generated from and where do they travel from there

A

Electrons stream from filament to cathode target

The negative cathode send electrons from cathode to anode (+)

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7
Q

Cathode

Filament

Focusing Cup

A
  • Filament
    • Tungsten wire
    • Filament is heated by flow of current from low voltage source and emits electrons proportional to tempurature
    • Electron cloud forms around filament
  • Focusing Cup
    • Molybdenum
    • Negatively charged reflector
    • Focuses electrons from filament into narrow beam directed to anode focal spot
      *
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8
Q

Anode

A
  • Tungsten target
  • Focal spot
    • Heat vs sharpness
    • Smaller= sharper image
    • Smaller= hotter
    • Copper stem- heat sink

The electrons smash onto tungsten target

  • Tungsten target is wrapped in copper to absorb heat
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9
Q

What happens at tungsten target

A

99% of energy converted to HEAT

Radiation is produced

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10
Q

Tungsten Properties

A
  • High atomic number Z
    • Efficient X ray production
  • High melting point
    • Withstand heat generated
  • High thermal conductivity
    • Helps dissipate heat
  • Low vapor pressure
    • Helps maintain vacuum in tube
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11
Q

Radiation definition

A

Transmission of energy though space and matter

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12
Q

Particulate Radiation

A
  • Large atoms= unstable
  • Atoms break up releasing
    • Alpha particles
    • Beta particles
    • Gamma rays
  • Radioactivity: The emission of ionizing radiation or particles by spontaneous disintegration of nucleus
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13
Q

Electromagnetic radiation definition

A

Movement of energy through space as a combination of electric and magnetic fields

Small discrete bundles of energy that are photons

An electron volt is the unit of energy of a photon

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14
Q

Electromagnetic radiation is generated when

A
  • EM radiation is generated when the velocity of an electrically charged particle is altered (accelerated or decelerated)
  • Velocity has magnitude and direction
  • If electron changes direction it releases energy in the form of radiation (X-ray)
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15
Q

Bremsstrahlung Radiation

A
  • The sudden stopping or slowing of electrons produces bremsstrahlung photons
  • Main mechanism to produce radiation produced in X ray beam
  • Direct hit
    • Electron can smash into the nucleus of the tungsten nucleus
    • Then all its mass and energy is converted into a photon (X-ray)
    • Strongest bc all of the energy of the electron is converted into a photon
  • Indirect hit
    • Negatively charged electron nearly misses the nucleus but is attracted to the nucleus
    • Changes direction, and velocity is a vector
    • Energy is released as a photon (xray) deacceleration
  • This is happening at the tungsten plate
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16
Q

Charecteristic Radiation

A
  • Moving electron hits and ejects inner electron
  • Outer orbital electron attracted to void
  • Must lose energy to go to lower energy state
  • Photon is emitted
  • Higher level/ outer shell electron will fall to a lower level shell
  • Called charactereistic bc every atom has its unique electron energy shell, characteristic to the element that it is involving
17
Q

Voltage

Definition

Deteremined by

Greater voltage potential leads to

A
  • Voltage is electromotive force (amplitude)
    • Movement of electrons across wire
  • Amplitude of the force is deteremined by the potential differnce between 2 points
  • Greater the voltage potential the greater
    • Greater push btw 2 plates
    • Higher energy of x ray
    • Electrons move faster
18
Q

Tube voltage

A
  • Between cathode and anode
  • Voltage across the tube
  • Want HIGH voltage kilovolts
  • Alternating current has spectrum of voltages, the highest is the peak, kVp usually 120
19
Q

Filament Voltage

A
  • Voltage across the filament
  • Want LOW voltage ~10 volts
  • Filament is very thin and can burn out easily
  • Thin so electrons can evaporate to make electron cloud
20
Q

Current

A
  • Amperage (Amps)
  • Measure of flow of the electrical charge
    • How many electrons are passing though a particular spot
  • Charge cant flow without voltage
  • Increase of Amps (current) more electrons more photons
21
Q

Filament Current

A
  • Number of electrons through filament
  • Increasing current through filament will increase tube current
22
Q

Tube Current

A
  • Number of electrons from cathode to anode
  • Filament (step down) transformer (low for filament voltage)
  • Reduces voltage of incoming AC current to 10 v
  • Voltage regulated by mA selector
  • System regulates filament temperature and number of electrons emitted by cathode to anode
  • Tube current=Number of electrons=Quantity of beam=Controlled by mA
23
Q

What are the 6 factors that control the X ray beam

A
  • Exposure time
  • Tube current
  • Tube voltage peak kVp
  • Filtration
  • Collimation
  • Inverse Square Law
24
Q

Exposure time

A

Measured in seconds

Number photons (quantity) proportional to number of seconds

Quality styas the same

25
Q

Tube Current in regards to x ray beam control

A
  • The number of photns that reach the film is proportional to the tube current
  • Works with exposure time
  • Quantity of radiation is proportional to product of time and current
  • 10 mA for 1 s= 20 mA for 0.5 s
  • Total number of photons in beam is = to beam quantity or beam intensity

Radiology (8 decks)

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