Rad 121 Chapter 7: The X-Ray Beam
Terms in this set (45)
ceiling support system
most common, has 2 sets of rails that allow for lateral and longitudinal movement, lock and raise and lower to obtain the correct distances
floor to ceiling support system
Has a single column with rollers at each end, one attached to the ceiling-mounted rail and the other attached to a floor-mounted rail.
when xray tube is aligned with the grid in the table
• most commonly used in angio-interventional system.
• so called because the system is shaped
like the letter "C".
• ceiling mounted and very flexible.
• image receptor is attached to the other end of the C-arm from the x-ray tube.
• other variations are the L-arm and the U-arm.
x-rays emitted through the window in an x-ray tube.
x-ray tube window
the rays used only go through this.
a material such as glass or porcelain with negligible electrical or thermal conductivity
oil absorbs much of the heat produced by X-ray production
glass or metal envelope
Encloses the entire cathode and anode assembly except the stator
support structure, protective housing, and glass or metal enclosure
What are the three parts of the external part of the x-ray tube?
cathode and anode
What are the internal parts of the x-ray tube?
a negatively charged electrode that is the source of electrons in an electrical device
a positively charged electrode by which electrons leave an electrical device. It conducts electricity and radiates heat and contains the target.
a coil of wire similar to that in a kitchen toaster.
is the giving off of electrons from the surface of a hot metal.
tungsten alloyed with thorium
a recessed area where the filament lies, directing the electrons toward the anode
filament and focusing cup
What are the primary parts of a cathode?
by controlling the filament current
How is the x-ray tube adjusted?
space charge limited
Themonic emission at low kVp and high mA can be _________________
space charge effect
Tendency of space charge electron cloud around cathode filament to limit further emission of electrons from filament.
filament current that has risen to its maximum value because all available electrons have been used
stationary and rotating
What are the two types of anodes?
a nonmoving anode, usually found in dental & small portable radiography units
an anode that turns on an axis to increase x-ray production while dissipating heat
electrical conductor, mechanical support, thermal dissipator, x-ray production
What are four primary functions of the anode?
materials that allow the flow of electrons emitted by the cathode and conducts them through the tube to the connecting cables and back to the high-voltage generator
copper, molybdeneum, and graphite
What are the most common anode materials?
area of the anode struck by the electrons from the cathode.
the target in the stationary anode consists of tungsten alloy embedded in the copper anode and the rotating anode tubes, the entire rotating disc is the target.
What is the difference between the target in a stationary anode and a target in a rotating anode?
atomic number, thermal conductivity, and high melting point
Why is tungsten the main material for the target for general radiography?
Allows the anode to rotate inside a glass envelope with no mechanical connection to the outside. Works on electromagnetic induction similar to that for a transformer and on Lenz' law of induced currents.
mechanical device consisting of the stationary part of a motor or generator in or around which the rotor revolves
electromagnetic induction motor
What powers the rotating anode?
In a new x-ray tube, the __________ is approximately 60s.
results in an effective focal spot size much less than the actual focal spot size.
ceiling support, floor to ceiling support, and c-arm support
List three methods used to support the x-ray tube.
in cathodes to provide more electrons, in anodes for physical strength and stability
Where in an x-ray imaging system is thoriated tungsten used?
the actual x-ray source
the smaller the anode angle, the larger. Also results in smaller effective focal spot and less radiation intensity on the anode side of the x-ray beam.
theoretical center of a beam of radiation
off focus radiation
xrays produced in anode but not at focal spot
electron arcing from filament to enclosure due to vaporized tungsten
What is the most frequent cause of abrupt tube failure?
A broken filament... As the filament becomes thinner, it eventually breaks
anode cooling chart
Conveys the capacity of the anode and its heat dissipation characteristics