Download Chapter 5 - RadTherapy

Chapter 5
X-ray Equipment
Diagnostic x-ray units:
 10 – 1200 mA
 10 second exposures
 25 – 150 kVp
Therapeutic x-ray units:
 20 mA
 1 – 60 minute exposures
 4 – 40 meV
Radiographic table: (bakelite / carbon fiber)
 Radiolucent: permits x-ray to travel through
 Flat or curved
 Easy to clean
 Space for film cassette and grid
 Bucky tray
 Tables move and/or float and lock
 Compression bands: uniform density, restraint
 Fixed or tilting
o Foot boards
o Shoulder supports / hand grips
Tube supports: move the tube around easily different directions
 Overhead – telescoping
 Floor to ceiling
 Mobile
 Floor mounted
 C – arm: mobile units, fluoroscopy
 Head units: floor to ceiling mounted
 Upright units: chest x-ray – fluid levels in chest, shoulder separation, cervical
spine x-rays, free air in abdomen
Special diagnostic equipment:
 Mammography units
 Dental panoramic units
 Pediatric unit: holds babies in position
 Tomography units: rotating mechanism, center is more clearly visualized, axial
scans (CT, PET CT)
 RTH simulator: similar to diagnostic, movement like treatment machine to
duplicate treatment
 Urology unit
Single-phase power: power supply that allows the potential difference to drop to zero
with every change in the direction of current flow. No potential difference and thus no xray production 120 times each second.
Three –phase power: power supply generated as each wave peak drops toward zero.
The overall potential difference is boosted back to peak by the next phase wave; the sum
of the phasing power never drops to zero.
Automatic exposure control: a device programmed to terminate the radiographic
exposure after a desired exposure has been reached. (photo-timer, ionization chamber)
 Allows tech to set kV only
 Back up law: 150%
o Generators must terminate at 600 mAs if ste above 50 kVp
o Generators must terminate at 2000 mAs if set below 50 kVp
Main circuit: supplies the x-ray tube with properly modified power to get the speed
necessary to make x-rays.
 Main switch: the switch that generates the power to the x-ray tube, contains power
box and circuit breakers.
 Exposure switch: a remote control device that permits current to flow by closing
the circuit and beginning the exposure; switch is depressed through duration,
activates rotating anode which is necessary for heat to be evenly distributed. Unit
can not make exposure until anode at the proper speed, dead mans switch is a
safety device;
 Autotransformer: a transformer that automatically sets by adjustments allows tech
to choose number of turns to increase / decrease voltage.
 Timer-circuit: device used to end the exposure at an accurately measured preset
time.
 Step-up transformer: a device used to increase the voltage from the primary to
secondary coil.
 Four-diode rectifier: electrons are permitted to flow in only one direction, turning
AC to DC.
Filament circuit: supplies the filament of the x-ray tube with properly supplied power to
produce an e-cloud by thermionic emission, an increase in voltage will then drive the
electrons to hit the anode target.
 Filament circuit variable resistance: allows change in voltage amount, incoming
voltage in decreased.
 Filament step-sown transformer: 3 – 5 A, 6 – 12 volts
X-ray tube:
Cathode: the negative side of the x-ray tube; produces a thermionic cloud, (Thermionic
emission: the ejection of electrons from the surface of the wire due to increased heat,
causing an electron cloud; also called the space charge cloud).
 Conducts the high voltage to the gap between the cathode and anode, and focuses
the electron stream as it heads for the anode.
 Anode: the positive side of the x-ray tube; serves as a target surface for high
voltage electrons from the filament, conducts high voltage from the cathode back
into the x-ray generator circuitry, and serves as the primary thermal conductor.
 Rotor: a hollow cylinder or cuff that is attached to the anode disk by a
molybdenum shaft.
 Stator: induction motor electromagnets that turn the anode.
Power rating of x-ray generators: determined by the greatest load the generator is
capable of sending to the tube and serves as a guide for the comparison of generators.