X-Ray Production & Emission by 8kebkY

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									X-Ray Production &
    Emission
       RTEC 111
   Bushong Ch. 8 & 9
Objectives:
 Reviewx-ray production
 requirements

 X-ray   tube interactions

 X-ray   emission spectrum
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
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
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
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
X-ray Tube Construction
            A




                B
                           D                 F
        C                                G
                                E


                Radiographic Equipment
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
E- traveling from cathode to anode

 Projectilee- interacts with the orbital
 e- of the target atom. This
 interaction results in the conversion
 of e- _______ energy into ________
 energy and ________ energy.
Tube Interactions
   3 possible tube interactions

   Tube interactions are generated from
    _____ slamming into ________?

Heat (99%), EM energy as infrared
radiation (heat) & x-rays (1%)
   X-rays = Characteristic (20%) or
    Bremsstrahlung (80%)
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
Heat is an excitation
rather than an ionization
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
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-
  It is called
characteristic
because it is
characteristic of
the target element
in the energy of
the photon
produced
Only K-characteristic x-rays of tungsten
are useful for imaging
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
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?
Bremsstrahlung

is a german
word meaning
slowed-down
radiation
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
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?

								
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