X-RAY PRODUCTION & X-RAY EMISSIONS by U03fK3Mu

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									X-RAY PRODUCTION &
  X-RAY EMISSIONS
    RADIATION PHYSICS
        TUBE INTERACTIONS
• Electron- Anode Interaction
  • Imagine the energy needed to propel electron
    from 0 to half the speed of light in one to three
    centimeters.
  • The electrons that travel from the cathode to the
    anode are called projectile electrons.
          X-RAY PRODUCTION

• Electron- Anode Interaction
  • When they strike the heavy metal atoms of the
    anode they interact with the atoms and transfer
    their kinetic energy to the target.
  • These interactions happen at a very small depth
    of penetration into the target.
    ELECTRON INTERACTION WITH
              TARGET
• The electrons
  interact with either
  the orbital electrons
  or nucleus of the
  target atoms.
• Interaction with the
  outer shell electrons
  produce heat
    ELECTRON INTERACTION WITH
              TARGET
• There is no
  ionization but there
  is excitation.
• More than 99% of
  the kinetic energy
  of the projectile
  electron is
  converted to
  thermal energy.
    ELECTRON INTERACTION WITH
              TARGET
• The production of
  heat increases
  directly with tube
  current.
• Through the
  diagnostic range,
  heat production
  increases directly
  with the increase of
  kVp.
   CHARACTERISTIC RADIATION

• When the projectile
  electron interacts
  with an inner shell
  electron of the
  target atom rather
  than with the outer
  shell electron,
  Characteristic X-
  radiation can be
  produced.
   CHARACTERISTIC RADIATION

• The interaction is
  sufficiently violent to
  Ionize the target
  atom by removing
  a K shell electron.
• A outer shell
  electron falls down
  to replace the lost
  electron.
   CHARACTERISTIC RADIATION

• The translation from
  outer shell electron
  to fill the hole in the
  K shell is
  accompanied by
  the emission of an x-
  ray photon.
• The K shell has an
  average energy of
  69 keV.
   CHARACTERISTIC RADIATION

• Only the K-
  characteristic x-rays
  are useful and
  contribute greatly
  to diagnostic
  radiographs.
   CHARACTERISTIC RADIATION

• Characteristic x-
  rays are produced
  by transitions of
  orbital electrons
  from the outer shell
  to the inner shell
  and is characteristic
  of the target
  element.
BREMSSTRAHLUNG RADIATION

            • Heat and
              Characteristic x-rays
              are the product of
              interaction with the
              electrons of the
              target atom.
            • There is a third type
              of interaction.
BREMSSTRAHLUNG RADIATION

            • The projectile
              electron can also
              interact with the
              nucleus of the target
              atom.
            • The nucleus has a
              strong positive
              charge.
            • The projectile
              electron misses all of
              the orbital electrons.
BREMSSTRAHLUNG RADIATION

            • And comes close to
              the nucleus.
            • The strong positive
              charge of the
              nucleus causes it to
              slow, lose kinetic
              energy and change
              direction.
BREMSSTRAHLUNG RADIATION

            • The lose of kinetic
              results in a low
              energy x-ray
              photon.
            • This type of x-rays
              are called
              Bremsstrahlung X-
              rays.
BREMSSTRAHLUNG RADIATION

            • Bremsstrahlung is a
              German word for
              braking.
            • This energy of x-ray
              is dependent upon
              the amount of
              kinetic energy in the
              interaction.
BREMSSTRAHLUNG RADIATION

            • A 70 keV electron
              can lose all, none or
              any intermediate
              level of kinetic
              energy.
            • The x-ray can have
              an energy range of
              0 to 70 keV.
BREMSSTRAHLUNG RADIATION

            • This is different from
              Characteristic X-ray
              that have a
              specified energy.
            • Low energy
              Bremsstrahlung x-
              ray result from slight
              interaction with the
              nucleus.
BREMSSTRAHLUNG RADIATION

            • Maximum strength
              Bremsstrahlung X-
              ray happen when
              the projectile
              electron loses all of
              it’s kinetic energy.
          CHARACTERISTIC VS.
       BREMSSTRAHLUNG X-RAYS.
• Characteristic X-ray require 70 kVp or higher. Based
  upon the energy of the k-shell electron.
• Bremsstrahlung X-rays can be produced at any
  projectile electron energy. In diagnostic
  radiography most of the x-rays are bremsstrahlung
  x-rays.
     X-RAY EMISSION SPECTRUM

• If a relative number of x-ray photons were plotted
  as a function of their energies we can analyze the
  x-ray emission spectrum.
• Understanding the x-ray emission spectra is key to
  understanding how changes in kVp, mA, time and
  filtration affects the optical density and contrast of
  the radiograph.
     DISCRETE X-RAY SPECTRUM

• Characteristic x-rays have a precisely fixed or
  discrete energies.
• These energies are characteristic of the differences
  between electron binding energies of a particular
  element.
• For tungsten you can have one of 15 energies .
     DISCRETE X-RAY SPECTRUM

• There are 15 energies
• There are 5 vertical
  line representing K x-
  rays.
• 4 representing L x-
  rays.
• Remaining represent
  lower energy outer
  shell electrons.
     DISCRETE X-RAY SPECTRUM

• K x-rays are the only
  characteristic x-rays
  of tungsten that
  have sufficient
  energy to be of
  value in
  radiography.
CONTINUOUS X-RAY SPECTRUM

             • The Bremsstrahlung
               x-ray energies
               range from zero to
               a peak and back to
               zero.
             • This is referred to as
               the Continuous X-
               ray Spectrum.
CONTINUOUS X-RAY SPECTRUM

             • The majority of the
               useful x-rays are in
               the continuous
               spectrum.
             • The maximum
               energy will be equal
               to the kVp of
               operation.
             • This is why it is called
               kVp (peak).
  FOUR FACTORS INFLUENCING THE
    X-RAY EMISSION SPECTRUM
• 1. The electrons accelerated from the cathode do
  not all have the peak kinetic energy. Depending
  upon the type of rectification and high voltage
  circuits, many electrons will have very low energy
  that produces low energy x-rays.
  FOUR FACTORS INFLUENCING THE
    X-RAY EMISSION SPECTRUM
• 2. The target is relatively thick. Many of the
  bremsstrahlung x-ray emitted result from multiple
  interactions of the projectile electrons.
• Each successive interaction results in less energy.
  FOUR FACTORS INFLUENCING THE
    X-RAY EMISSION SPECTRUM
• 3. Low energy x-rays are more likely absorbed by
  the target.
• 4. External filtration is always added to the tube
  assembly. This added filtration serves to selectively
  remove the lower energy photon.
      MINIMUM WAVELENGTH

• As a photon wavelength increases, the photon
  energy decreases. Therefore the maximum x-ray
  energy is associated with the minimum x-ray
  wavelength.
• Since the minimum wavelength of x-ray emissions
  corresponds to the maximum photon energy, the
  maximum photon energy is equal to the kVp.
               INTEGRATION

• The total number of x-rays emitted from an x-ray
  tube could be determined by adding the number
  of x-rays emitted at each energy level over the
  entire spectrum.
• This is referred to as integration.
FACTORS AFFECTING THE SIZE AND RELATIVE
 POSITION OF THE X-RAY EMISSION SPECTRA.



 • Tube Current (mA) effects the amplitude
 • Tube Voltage effects the amplitude and position.
 • Added Filtration effects Amplitude most effective at
   low energies.
FACTORS AFFECTING THE SIZE AND RELATIVE
 POSITION OF THE X-RAY EMISSION SPECTRA



• Target material effects spectrum and position of the
  line spectrum.
• Voltage waveform effects the amplitude, most
  effective at high energies
  INFLUENCE OF TUBE CURRENT

• A change in mA or
  mAs results in a
  proportional
  change in the
  amplitude of the x-
  ray emission
  spectrum at all
  energies and the
  intensity of the
  output.
 INFLUENCE OF TUBE POTENTIAL

• Unlike tube current,
  a change in kVp
  affects both the
  amplitude and the
  position of the x-ray
  emission spectrum.
 INFLUENCE OF TUBE POTENTIAL

• When kVp increases
  the relative
  distribution of
  emitted photons
  shifts to the right or
  to higher energies.
• 15% increase in kVp
  is equivalent to
  doubling the mAs.
INFLUENCE OF ADDED FILTRATION

               • Adding filtration to
                 an x-ray machine
                 has an effect on
                 the relative shape
                 of the spectrum
                 similar to that of
                 increasing the kVp.
INFLUENCE OF ADDED FILTRATION

               • Added filtration
                 effectively absorbs
                 more low energy x-
                 ray than high
                 energy x-rays,
                 therefore the
                 spectrum is
                 reduced more to
                 the left.
             X-RAY FILTRATION

• Filtration of the x-ray
  beam has two
  components:
  • Inherent Filtration
  • Added Filtration
• Filtration is required
  by law.
• Aluminum is most
  common material.
 FILTRATION AFFECTS THE BEAM
          SPECTRUM
• Filtration removes
  the lower energy
  photons that do not
  contribute to image
  production.
• Added filtration
  results in an
  increased half
  value layer or
  higher quality
  beam.
INFLUENCE OF ADDED FILTRATION

               • The overall result is
                 an increase in the
                 effective energy of
                 the beam
               • The discrete and
                 maximum energy of
                 the x-ray spectrum
                 is not effected.
INFLUENCE OF TARGET MATERIAL

• As the atomic number of the target material
  increases, the efficiency of the continuous spectrum
  x-rays increase.
• The discrete spectrum also shifts to the right
  representing higher energy characteristic radiation.
• Tungsten is used for general radiography.
INFLUENCE OF TARGET MATERIAL

• Some specialty tube use gold.
• Molybdenum is used for mammography. It has a
  lower atomic number so the discrete spectrum is of
  a lower energy. This is ideal for soft tissue studies
  such as mammography.
INFLUENCE OF VOLTAGE WAVEFORM

• As the voltage
  across the x-ray
  tube increases for
  zero to its peak, the
  intensity and energy
  increase slowly at
  first and then rapidly
  as the peak voltage
  is obtained.
INFLUENCE OF VOLTAGE WAVEFORM

• The x-ray intensity is
  not proportional to
  the voltage.
• The intensity is much
  higher at peak
  voltage than at
  lower voltages.
TYPE OF X-RAY VOLTAGE

           • High frequency or
             three phase
             voltage waveforms
             will result in
             considerably more
             intense x-ray
             emission.
TYPE OF X-RAY VOLTAGE

           • Operation on three
             phase equipment is
             equivalent to a 12%
             increase over single
             phase equipment.
           • High Frequency is a
             16% increase.
SINGLE-PHASE TO HIGH FREQUENCY

• With the spectrum shifted to the right or higher
  intensity, the change in mAs for this conversion is to
  reduce mAs by 50%.
• 30 mAs single phase = 15 mAs High Frequency or
  Three Phase.
              X-RAY EMISSION

• The output intensity is measured in roentgens ( R) or
  milliroentgens (mR) and is termed the X-ray
  Quantity.
• Radiation Exposure is often used instead of x-ray
  intensity or X-ray Quality.
• The number of x-rays in the useful beam is the
  Radiation Quantity.
  ESTIMATING X-RAY INTENSITY

• Using a nomogram,
  we can estimate
  the exposure
  output over a wide
  range of technical
  factors.
• Important factors
  are:
• Filtration
• kVp
   ESTIMATING X-RAY INTENSITY

• Exposure is
  expressed as
  mR/mAs.
• With 3mm of Al
  filtration at 70 kVp
  the output is about
  5 mR/mAs
• At 100 mAs, the
  exposure would be
  500 mR.
FACTORS AFFECTING X-RAY QUANTITY

• A number of factors affect X-ray Quantity. Theses
  same factors also control radiographic film density:
• Milliamperage- Seconds
• kVp
• Distance
• Filtration
           MA X TIME (S)= MAS

• The X-ray quantity is directly proportional to the
  mAs. If we double the mAs, the number of electrons
  striking the target is doubled.
• 300 mA @ 1/30 second = 10 mAs
• 200 mA @ 1/20 second = 10 mAs
• 100 mA @ 1/10 second = 10 mAs
               KILOVOLTAGE

• X-ray quantity varies rapidly with changes in kVp.
• The change in quantity is proportional to the square
  of the ratio of the change.
• If the kVp is doubled, the intensity would increase
  by a factor of four.
               KILOVOLTAGE

• What really happens when the kVp is increased?
• When kVp is increased, the penetrability of the x-
  rays is increased and relatively fewer x-rays are
  absorbed in the patient.
• More rays pass through the patients to interact with
  the film.
              KILOVOLTAGE

• To maintain a constant exposure of the film, an
  increase of 15% in kVp should be accompanied by
  a reduction of one half the mAs.
                    DISTANCE

• Radiation intensity from an x-ray tube varies
  inversely with the square of the distance from the
  target. This is referred to as the inverse square law.
• It is the same for any type of electromagnetic
  energy.
              FILTRATION

• X-ray machines
  have metal filters
  inserted into the
  useful beam.
• The primary purpose
  is the remove the
  low energy beam
  that reach the
  patient and are
  absorbed
  superficially.
              FILTRATION

• These low energy
  photons contribute
  nothing to the
  formation of the
  radiographic
  image.
• Filters therefore
  reduce patient
  exposure.
               FILTRATION

• Calculation of the
  amount of exposure
  reduction requires a
  knowledge of the
  Half-Value Layer.
              X-RAY QUALITY

• As the effective energy of the beam is increases,
  the penetrability is also increased.
• Penetrability refers to the range of beam in matter;
  high energy beams are able to penetrate matter
  farther than low energy beams.
• Beams with high penetrability are referred to as
  hard.
            X-RAY QUALITY

• Beams of low quality are called soft beams.
• X-ray quality is identified numerically by HVL.
• The HVL is affected by the kVp of operation and
  the amount of filtration in the useful beam.
• X-ray quality is influenced by the kVp and
  filtration.
      HALF-VALUE LAYER (HVL)

• Half-value layer is the thickness of absorbing
  material needed to reduce the intensity to one half
  of its original value.
• HVL is a characteristic of the x-ray beam.
• A Diagnostic x-ray beam usually has an HVL of 3 to
  5 mm Al.
        DETERMINING THE HVL

• An exposure is
  made without
  filtration and the
  intensity is
  measured.
• Different thickness
  of filtration is added
  and intensity is
  measured.
• Results are
  graphed.
        DETERMINING THE HVL

• From the graph, the
  HVL can be
  determined.
• The established
  standard for
  filtration is 2.5 mm Al
  for tube operated
  above 70 kVp.
           HALF-VALUE LAYER

• HVL is the best method for specifying x-ray quality.
• Variations of kVp and filtration are not simple
  relationships. A tube with 2mm Al operated at 90
  kVp may have the same HVL as when operated at
  70 kVp with 5 mm AL.
           HALF-VALUE LAYER

• The penetrability remains constant as does the HVL.
FACTORS AFFECTING X-RAY QUALITY

• Kilovoltage. As the kVp is increased, so is beam
  quality and therefore HVL.
• An increase in kVp results in a shift of the x-ray
  emission spectrum towards the higher energy side.
• This increases the effective energy of the beam,
  making it more penetrating.
 RELATIONSHIP BETWEEN KVP AND
       HVL WITH 2.5 MM AL
• kVp           • HVL ( mm AL)
• 50            • 1.9
• 75            • 2.8
• 100           • 3.7
• 125           • 4.6
FACTORS AFFECTING X-RAY QUALITY

• Filtration. The
  primary purpose of
  adding filtration to
  the x-ray beam is to
  remove low energy
  x-rays that have no
  chance of getting
  to the film.
FACTORS AFFECTING X-RAY QUALITY

• As filtration is
  increased, so is the
  beam quality, but
  quantity is
  decreased.
         TYPES OF FILTRATION

• There are three types of filtration:
• Inherent Filtration: Glass envelope window equals
  about 0.5mm Al
• Added Filtration: Added in collimator
• Compensating Filtration: Used to improve image
  quality or radiation reduction
         INHERENT FILTRATION

• The glass envelope of the tube filters the emerging
  beam. In diagnostic x-ray tubes the glass is equal to
  about 0.5 mm Al.
• As tube ages and more tungsten is vaporized,
  tungsten will build up on the inside of the tube that
  will add more filtration.
           ADDED FILTRATION

• One or two mm of aluminum is added filtration
  placed in the collimator. This filtration is generally
  placed on the mirror of the collimator.
• This filtration attenuates x-rays of all energies
  emitted from the tube. This shifts the spectrum to the
  high side.
           ADDED FILTRATION

• This shift in the emission spectrum results in a beam
  with higher effective energy, greater penetrability
  and higher quality.
• This results in an increased half value layer.
• The minimum filtration for tube operated above 70
  kVp is 2.5 mm Al equivalence.
       COMPENSATING FILTERS

• Compensating
  filters are added to
  the beam by the
  operator to
  compensate for
  differences in
  subject tissue
  density or type.
        COMPENSATING FILTERS

• In areas of the body where there are great
  differences in tissue density, compensating filters are
  used to reduce exposure in the area of less density.
• This reduced patient exposure and improves image
  quality. The thoracic spine and full spine x-rays need
  filtration.
      COMPENSATING FILTERS

• This is the 40”
  Cervicothoracic
  Compensating
  Filter.
• It may be called the
  thyroid filter as it
  reduces the
  exposure to the
  upper thorax.
COMPENSATING FILTERS

           • This heart shaped
             filter is used to
             reduce exposure to
             the ovaries of
             females of child
             bearing age.
           • It reduces exposure
             by about 85%.

								
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