X-Ray Production

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X-Ray Production Emission
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PRODUCTION OF X RAYS

• Requirements
• a source of fast moving electrons
• must be a sudden stop of the electrons motion
• in stopping the electron motion, kinetic energy
  (KE) is converted to EMS energies
• Infrared (heat), light x-ray energies

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How X-rays are created

• Power is sent to x-ray tube via cables
• mA (milliamperage) is sent to filament on cathode
  side.
• Filament heats up electrons boil off
• Negative charge

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How X-rays are created

• Positive voltage (kVp) is applied to ANODE
• Negative electrons attracted across the tube to
  the positive ANODE.
• Electrons slam into anode suddenly stopped.
• X-RAY PHOTONS ARE CREATED

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How X-rays are created

• Electron beam is focused from the cathode to the
  anode target by the focusing cup
• Electrons interact with the electrons on the
  tungsten atoms of target material
• PHOTONS sent through the window PORT towards
  the patient

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Principle Parts of the X-ray Imaging System

• Operating Console
• High-voltage generator
• X-ray tube
• The system is designed to provide a large number
  of e- with high kinetic energy focused to a small
  target

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E- traveling from cathode to anode

• Projectile e- interacts with the orbital e- of
  the target atom. This interaction results in the
  conversion of e- _______ energy into ________
  energy and ________ energy.

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Heat

• Most kinetic energy of projectile e- is converted
  into heat 99
• Projectile e- interact with the outer-shell e- of
  the target atoms but do not transfer enough
  energy to the outer-shell e- to ionize

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Heat is an excitation rather than an ionization
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Heat production

• Production of heat in the anode increases
  directly with increasing x-ray tube current kVp
• Doubling the x-ray tube current doubles the heat
  produced
• Increasing kVp will also increase heat production

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Characteristic Radiation 2 steps

• Projectile e- with high enough energy to totally
  remove an inner-shell electron of the tungsten
  target
• Characteristic x-rays are produced when
  outer-shell e- fills an inner-shell void
• All tube interactions result in a loss of kinetic
  energy from the projectile e-

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• It is called
• characteristic
• because it is
• characteristic of
• the target element
• in the energy of
• the photon
• produced

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Only K-characteristic x-rays of tungsten are
useful for imaging
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Bremsstrahlung Radiation

• Heat Characteristic produces EM energy by e-
  interacting with tungsten atoms e- of the target
  material
• Bremsstrahlung is produced by e- interacting with
  the nucleus of a target tungsten atom

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Bremsstrahlung Radiation

• A projectile e- that completely avoids the
  orbital e- as it passes through a target atom may
  pass close enough to the nucleus of the atom to
  convert some of the projectile e- kinetic energy
  to EM energy
• Because of the electrostatic force?

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Bremsstrahlung

• is a german
• word meaning
• slowed-down
• radiation

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X-ray energy

• Characteristic x-rays have very specific
  energies. K-characteristic x-rays require a tube
  potential of a least 70 kVp
• Bremsstrahlung x-rays that are produced can have
  any energy level up to the set kVp value. Brems
  can be produced at any projectile e- value

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Discrete spectrum

• Contains only specific values

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Continuous Spectrum

• Contains all possible values

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Characteristic X-ray Spectrum

• Characteristic has discrete energies based on the
  e- binding energies of tungsten
• Characteristic x-ray photons can have 1 of 15
  different energies and no others

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Characteristic x-ray emission spectrum
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Bremsstrahlung X-ray Spectrum

• Brems x-rays have a range of energies and form a
  continuous emission spectrum

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Factors Affecting the x-ray emission spectrum

• Tube current, Tube voltage, Added filtration,
  Target material, Voltage waveform
• The general shape of an emission spectrum is
  always the same, but the position along the
  energy axis can change

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Quality

• The farther to the right the higher the effective
  energy or quality

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Quantity

• The more values in the curve, the higher the
  x-ray intensity or quantity

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mAs

• A change in mA or s or both results in the
  amplitude change of the x-ray emission spectrum
  at all energies
• The shape of the curve will remain the same

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mA increase from 200 to 400
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kVp

• A change in voltage peak affects both the
  amplitude and the position of the x-ray emission
  spectrum

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Filtration

• Adding filtration is called hardening the x-ray
  beam because of the increase in average energy
• Characteristic spectrum is not affected the
  maximum energy of x-ray emission is not affected

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Filtration

• Adding filtration to the useful beam reduces the
  x-ray beam intensity while increasing the average
  energy
• Added filtration is an increase in the average
  energy of the x-ray beam (higher quality) with a
  reduction in x-ray quantity
• Lowering the amplitude and shifting to the right

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What kVp does this graph indicate?
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Target Material

• The atomic number of the target affects both the
  quantity and quality of x-rays
• Increasing the target atomic number increases the
  efficiency of x-ray production and the energy of
  characteristic and bremsstrhlung x-rays

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Target material
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Voltage Waveform

• 5 voltage waveforms half-wave rectification,
  full-wave rectification, 3-phase/6-pulse,
  3-phase/12-pulse, and high-frequency.
• Maintaining high voltage potential

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Voltage generators
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X-ray Quantity or Intensity

• What units of measurement is used for radiation
  exposure or exposure in air?
• Milliampere-seconds (mAs) x-ray quantity is
  proportional to mAs
• Kilovolt Peak (kVp) If kVp were doubled the
  x-ray intensity would increase by a factor of
  four or kVp2

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X-ray Quantity or Intensity

• Distance x-ray intensity varies inversely with
  the square of the distance from the x-ray target
• When SID is increased, mAs must be increased by
  SID2 to maintain constant OD

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Filtration

• 1 to 3 mm of aluminum (Al) added to the primary
  beam to reduce the number of low-energy x-rays
  that reach the patient, reducing patient dose
• Filtration reduces the quantity of x-rays in the
  low-energy range

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Reducing low-energy photons
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X-ray Quality or Penetrability

• As the energy of an x-ray beam is increased, the
  penetrability is also increased
• High-energy photons are able to penetrate tissue
  farther than low-energy photons
• High-quality high-penetrability
• Low-quality low-penetrability

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HVL Half-Value Layer

• What is the HVL
• HVL is affected by the kVp and added filtration
  in the useful beam
• Photon quality is also influenced by kVp
  filtration
• HVL is affected by kVp

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HVL

• In radiography, the quality of the x-rays is
  measured by the HVL
• The HVL is a characteristic of the useful x-ray
  beam
• A diagnostic x-ray beam usually has an HVL of 3
  to 5 mm Al

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HVL

• 3 to 5 mm Al to 3 to 6 cm of soft tissue
• HVL is determined experimentally and a design
  specification of the equipment

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X-ray Quality

• Kilovolt Peak (kVp) increasing the kVp
  increased photon quality and the HVL

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Types of Filtration

• Diagnostic x-ray beams have two filtration
  components inherent filtration and added
  filtration
• Inherent filtration The glass enclosure of the
  tube (the window) approximately 0.5 mm Al
  equivalent

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Added Filtration

• 1 or 2 mm sheet of aluminum between the tube
  housing and the collimator
• The collimator contributes an additional 1mm Al
  equivalent added filtration

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Compensating filter

• A filter usually made of Al, but plastic can be
  used to maintain OD when patient anatomy varies
  greatly in thickness
• Are useful in maintaining image quality. They are
  not radiation protection devices