The ray Imaging System

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					The X-ray Imaging
     System
           Radiographic Tables
• Tilting or Non-tilting
• Free-floating , motorized
  or stationary top
• Adjustable or non-
  adjustable height
            Tilting or Non tilting
• Tilting
  – 90-90 tilting table
     • Can tilt from the horizontal position to a complete
       vertical position in either direction
  – 90-30 tilting table
     • Can tilt from the horizontal position to a complete
       vertical position in one direction and to a 30 degree tilt in
       the other direction
   Free floating or Stationary top
• Free floating
   – Has a locking mechanism that when it is turned off, allows
     the radiographer to move the table top manually
• Motorized
   – Has a switch that drive the table top in the desired direction
• Stationary
   – The table top does not move, the radiographer must move
     the patient
Adjustable or Non-adjustable Height
• Adjustable
  – The height of the table can be adjusted to a
    comfortable level for the patient and technologist
• Non-adjustable
  – The height may not be adjusted
                 Tube Stands
•   Floor mounted
•   Floor to wall mounted
•   Floor to ceiling mounted
•   Table supported
•   Overhead suspension
    Radiographic Room Design
• Radiographic only
  – Will be utilized to produce only over head films
• Radiographic and Fluoroscopic (R/F or R & F)
  – Will be utilized to produce over head films and
    fluoroscopic images
     • Bucky Slot Cover
        – During fluoro the Bucky must be covered so that radiation may
          not be scattered from the x-ray tube toward the radiographer or
          radiologist
       Imaging System Design
• Operating console
• High-voltage generator
• X-ray tube
            Operating Console
• mA control
  – Controls Quantity or the number of x-rays and is
    expressed in mAs
• kVp control
  – Controls Quality or the penetrability of the x-ray
    beam and is expressed in kVp
• Line compensation
• Autotransformer
• Exposure timers
                mA control
• Controls the number of electrons crossing from
  cathode to anode per second and is measured in
  milliampers (mA)
• X-ray tube current is controlled through a
  separate circuit called the filament circuit
              Filament circuit
• Filament
  – Coil of wire that when a current is supplied will heat
    up and actually allow electrons to be emitted from
    the coil
• Operates at between 3 and 6 A
  – Voltage from the autotransformer is stepped down
    so that the appropriate mA can be selected.
      Autotransformer                  HV
                                                     Rectifiers
                                   Transformer




                               Timer                              X-ray Tube



                           kVp
                           Meter


Line
Voltage
                         mA
60 Hz AC                Selector




                                        Filament
The General X-ray Circuit              Transformer
                   kVp Control
• kVp determines the quality or the penetrability
  of the x-ray beam
  – Major kVp
     • Selects the kVp by factors of 10
  – Minor kVp
     • Selects the kVp by factors of 1
     A combination of major and minor kVp gives the
       appropriate kVp readout for an exposure
           Line Compensator
• Compensates the incoming voltage so that a
  constant voltage may be used during exposure
  and not a varying voltage
             Autotransformer
• Designed to supply the precise voltage to the
  filament circuit and to the high voltage circuit of
  the x-ray imaging system.
              Exposure timers
•   Mechanical timers
•   Synchronous timers
•   Electronic timers
•   mAs timers
•   Automatic exposure control timers
             Mechanical Timers
• A preset exposure time is
  dialed by turning a knob
  that winds a spring.
  When the exposure
  button is depressed, the
  spring is released.
   – Used mostly in dental
     units and some portable
   – Not very accurate
   – Very inexpensive
          Synchronous timers
• Driven by a synchronous motor which operates
  at 60 revolutions per second
  – Recognizable because exposure times are in intervals
    of 60 (1/60s, 1/20 s, 1/30 s)
  – Have to be reset after each exposure
            Electronic timers
• The most expensive, most complicated and
  most accurate of the x-ray timers
  – Composed of complex circuitry
  – Allow for a wide range of intervals
  – Can be used to make serial exposures
                 mAs timers
• An electronic timer
  – T he technologist selects the mAs and when the
    desired mAs is reached the exposure is terminated
 Automatic exposure control timers
• The exposure will automatically terminate the
  exposure when sufficient radiation to provide
  the required optical density has reached the
  image receptor.
  – AEC measures the quantity of radiation reaching the
    image receptor
  – Controlled by kVp setting
  – Operates best at high kVp levels
       High Voltage Generator
• Converts the low voltage supplied from the
  power company into high Kilovoltage required
  to produce x-rays and the high Amperage to the
  milliamperage needed to produce current to the
  filament
       High Voltage Generator
• High voltage transformer
   – A step-up transformer
• The filament transformer
   – A step-down transformer
• Rectifiers
   – Converts AC to DC
                   Rectifiers
• Rectification is required to ensure electron flow
  in only one direction in the x-ray tube, from
  cathode to anode.
  – Vacuum tube rectifiers
  – Solid State rectifiers
      Vacuum Tube Rectifiers
• Composed of a cathode and an anode
  – Cathode is negative end
     • Contains a coil of wire that is heated so that it releases
       electrons by thermionic emission
  – Anode is positive end
     • Attracts the electrons so that electrons flow from negative
       to positive.
          Solid-State Rectifiers
• Also called a solid state diode
• Composed of two types of semi-conductors
  – P-type
     • Have electron traps made up of positively charged holes
       that tend to attract and hold electrons
  – N-type
     • Have loosely bound electrons that are relatively free to
       move about inside the material
          Unrectified Voltage
• Voltage at the primary and secondary side of the
  high voltage step-up transformer is Unrectified
• Rectification takes place between the secondary
  side of the step up transformer and the x-ray
  tube.
• Waveform is a sinusoidal wave
       Half-wave Rectification
• The inverse (negative) voltage is removed from
  the wave making all voltage positive
• Only half of the AC waveform appears in the
  output
  – Disadvantage
     • Waste half of the incoming power supply
        Full-wave Rectification
• Converts the negative half of the AC wave form
  into positive wave form that can be used in x-ray
  production
• Must have 4 rectifiers to accomplish full wave
  rectification
           Single-phase Power
• Allows the incoming power to pulsate due to the
  rise and fall of current
• Full voltage ripple
  – 100%
           Three-phase power
• 3 wave forms are provided, so that the resulting
  waveform maintains a nearly constant high
  voltage.
  – Three phase six pulse
     • Characterized by 6 pulses every 1/60 sec
  – Three phase 12 pulse
     • Characterized by 12 pulses every 1/60 sec
• 4% voltage ripple
     High Frequency Generator
• Instead of using 60 pulses per second for
  incoming voltage, it used 500 pulses per second
• The most efficient of all x-ray generators
• 1% voltage ripple
  Capacitor Discharge Generator
• This is a battery type usually portable unit.
• Discharges pre-selected amount of energy from
  a rechargeable battery unit.
               Voltage Ripple
•   Half wave = 100 %
•   Full wave = 100%
•   Three phase six pulse = 13%
•   Three phase twelve pulse = 4 %
•   High frequency = <1 %
           X-ray circuit
• Pg 126
The End

				
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