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					X-ray production

  Noreen Marwat
    SS PAEC
      X-ray Tube Rating Charts
• With careful use, the x-
  ray tube can provide long
  periods of service.
• Inconsiderate or careless
  operation can lead to
  shortened life or abrupt
  failure.
• X-ray tubes are very
  expensive. Cost varies
  from $2,000 to $20,000.
    X-ray Tube Rating Charts
• Tube life is extended by :
• Use of minimum mAs & kVp appropriate
  for the exam.
• Use of faster images receptors require
  lower mAs and kVp. They extend tube life.
 Causes of X-ray Tube Failure
• All causes of tube failure relate to the
  thermal characteristics of the tube.
• When the temperature of the anode during
  a single exposure is excessive, localized
  melting and pitting occurs.
• These surface irregularities lead to
  variable and reduced radiation output.
  Causes of X-ray Tube Failure
• If the melting is severe, the tungsten
  vaporizes and can plate the port. This can
  cause added filtering or interference with
  the flow of electrons.
• If the temperature of the anode increases
  to rapidly,the anode can crack and then
  become unstable in rotation.
  Causes of X-ray Tube Failure
• Maximum
  radiographic
  techniques must
  never be applied to
  a cold anode.
• These images show
  damage to the anode,
  Causes of X-ray Tube Failure
• During long
  exposures (1 to 3
  seconds) the anode
  may actually glow like
  a light bulb.
• The heat may cause
  a failure of the
  bearing for the anode
  or a crack in the glass
  envelope.
            Filament failure
• Because of the high heat of the filament,
  tungsten atoms are slowly vaporized and
  plate the inside of the glass envelope. This
  will eventually lead to arcing and tube
  failure.
• Continuous high mA radiography will
  actually lead to the filament breakage.
   Tube Warm-up Procedures
• By warming the anode through a series of
  exposures and increasing kVp settings,
  the anode will build up heat that is needed
  to avoid fracture of the anode.
• This process takes a little over one minute
  put will add to the life of the tube.
• Close shutters of collimator.
     Tube Warm-up Procedures
•   Make exposure of 12 mAs @ 70 kVp
•   Wait 15 seconds
•   Make exposure of 12 mAs @ 80 kVp
•   Wait 15 seconds
•   Make exposure of 12 mAs @ 90 kVp
•   Tube warm up is now complete.
    X-ray Tube Rating Charts
• It is essential for the x-ray operator to
  understand how to use tube rating charts.
• There are three types of charts:
  – Radiographic Rating Chart
  – Anode Cooling Chart
  – Tube Housing Cooling Chart
   Radiographic Rating Charts
• A tube may be used
  in many ways with
  many variables. Such
  as:
  – Large or Small Focal
    spot
  – 10,000 RPM or 3,400
    RPM Rotor Speed
  – Single-phase or high
    frequency power.
   Radiographic Rating Charts
• Even the angle of the
  anode is important.
• Always look at the
  correct chart.
• The x-axis and y-axis
  are graduated in kVp
  and time.
   Radiographic Rating Charts
• The mA is graphed as
  a curved line.
• Any combination of
  kVp and Time below
  the line should be
  safe for a single
  exposure.
   Radiographic Rating Charts
• Most machine has
  built-in protection to
  help you avoid tube
  overload.
• Microprocessor
  controlled generator
  way display the
  percent of tube load.
Anode Cooling Chart
          • The anode has a
            limited capacity for
            storing heat.
          • Heat is continuously
            dissipated to the oil
            bath and tube
            housing by
            conduction and
            radiation.
Anode Cooling Chart
          • It’s possible through
            prolonged use of
            multiple exposures to
            exceed the heat
            storage capacity of
            the anode.
          • Thermal energy in x-
            ray is measured in
            Heat Units (HU)
Anode Cooling Chart
         • HU= kVp x mA x time (s)
         • This chart is not dependent
           upon the filament size or
           speed of anode rotation
         • The cooling is rapid at first
           but slows as the anode
           cools. It is not uncommon
           for it to take 15 minutes to
           cool the tube.
     Housing Cooling Charts
• The tube housing cooling chart is very
  similar to the anode cooling chart.
• The tube housing will generally have a
  capacity of about 1 to 1.5 million HU.
• Complete cooling may take 1 to 2 hours.
X-Ray production
X-ray Production
the internal components
of the x-ray tube, the cathode and anode,
within the evacuated glass metal enclosure.
ELECTRON TARGET
  INTERACTIONS
kVp   KINETIC ENERGY OF ELECTRONS
  ELECTRON TARGET INTERACTIONS

The three principal parts of an x-ray imaging
 system the operating console, the high-
 voltage generator, and the x-ray tube-are
 all designed to provide a large number
of electrons with high kinetic energy
 focused to a small spot on the anode
         Production of X-rays

• X-rays are produced when rapidly moving
  electrons that have been accelerated through a
  potential difference of order 1 kV to 1 MV strikes
  a metal target.
     Evacuated
     glass tube




          Target

                                    Filament
           Production of X-rays
• Electrons from a hot element are accelerated
  onto a target anode.
• When the electrons are suddenly decelerated on
  impact, some of the kinetic energy is converted
  into EM energy, as X-rays.
• Less than 1 % of the energy supplied is
  converted into X-radiation during this process.
  The rest is converted into the internal energy of
  the target.
The modern x-ray imaging system is
remarkable. It conveys to the x-ray tube
target an enormous number of electrons at
a precisely controlled kinetic energy. At
100 mA, for example, 6 X 1017 electrons
travel from the cathode to the anode of the
x-ray tube every second
In an x-ray imaging system operating at 70
  kVp, each electron arrives at the target
  with a maximum kinetic energy of 70 keV.
  Because there are 1.6 X 10-16 J per
1 keV, this energy is equivalent to the
  following:
The electrons traveling from cathode to
 anode constitute the x-ray tube current
 and are sometimes called projectile
 electrons. When these projectile electrons
 hit the heavy metal atoms of the x-ray tube
 target, they transfer their kinetic energy to
 the target atoms.
    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.
The efficiency of x-ray production
increases with increasing kVp. At 60 kVp,
only 0.5% of the electron kinetic energy is
converted to x-rays. At 100 kVp,
approximately 1% is converted to x-rays,
and at 20 MV, 70% is converted.
Characteristic Radiation
            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 CASCADE
TUNGSTEN-74
            BINDING ENERGIES
      OF DIFFERENT SHELL ELECTRONS




                K-70 KEV
                L-12 KEV
                M-2.8 KEV
    CHARACTERISTIC X-RAYS




L           K               70-12 = 58 keV



M           K               70-3 = 67 keV



M
            L               12-3 = 9 keV
TRANSFER OF ELECTRONS
 BETWEEN OUTER SHELLS
      RESULTS IN:



     HEAT PRODUCTION !
             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
BREMS
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.
DIFFERENT DEGREES OF
    DECCELERATION
             X-RAYS




      HEAT
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.
             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
         Discrete spectrum
• Contains only specific values
       Continuous Spectrum
• Contains all possible values
 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
Characteristic x-ray emission
         spectrum
Bremsstrahlung X-ray Spectrum
• Brems x-rays have a range of energies
  and form a continuous emission spectrum
          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
                  Quality
• The farther to the right the higher the
  effective energy or quality
                Quantity
• The more values in the curve, the higher
  the x-ray intensity or quantity
                   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
mA increase from 200 to 400
                   kVp
• A change in voltage peak affects both the
  amplitude and the position of the x-ray
  emission spectrum
                 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
                 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
What kVp does this graph
       indicate?
            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
    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
Target material
          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
Voltage generators
    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
    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
                 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
Reducing low-energy photons
  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
      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
                    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
                    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
             X-ray Quality
• Kilovolt Peak (kVp) = increasing the kVp
  increased photon quality and the HVL
          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
           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
         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
Wedge filter
        Compensating Filter
• What is an aspect of the tube design that
  works as a compensating filter?

• What causes this?
Questions?
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
   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
    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
     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
      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
            FILTRATION
• These low
  energy photons
  contribute
  nothing to the
  formation of the
  radiographic
  image.
• Filters therefore
  reduce patient
           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.
   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
•50          AL)
•75         •1.9
•100        •2.8
•125        •3.7
            •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
 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

				
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