X-ray Tube Ch 7 Flashcards
It converts electrical energy to
electromagnetic energy
X-ray Tube
Any tube with two electrodes
Diode
External Structures if X-ray tube
Support Structure, Protective Housing &
Glass/Metal Enclosure
It consists of two perpendicular sets of
ceiling-mounted rails
Ceiling-Support System
When x-ray tube is centered above the
examination table at the standard SID
Preferred Detent Position
It consists a single column with rollers at
each end
Floor-To-Ceiling Support System
It provides for very flexible x-ray tube
positioning
C-Arm Support System
Lead-lined metal container into which the xray tube is fitted
Protective Housing
Emission with equal intensity in all
directions
Isotropic Emission
A thin section of a glass/metal envelope
through which useful beam emerges
Window
X-rays emitted through the window
Useful Beam/Primary Radiation
X-rays that escape through protective
housing
Leakage Radiation
It contains the x-ray tube & its components
Glass/Metal Enclosure
Glass Enclosure
Pyrex glass
o Able to withstand tremendous heat
generated
Maintain constant electric potential between
the electrons of the tube current & the
enclosure
Metal Enclosure
The negative side of the x-ray tube
Cathode
2 primary parts of Cathode
filament & focusing cup
A coil of wire that emits electrons when it is
heated
Filament
Metal shroud that surrounds the filament
Focusing Cup
most common cause of tube failure
Tungsten vaporization with deposition on the
inside of the glass enclosure
Cloud of electrons
Space Charge
A phenomenon of the space charge that
makes it difficult for subsequent electrons to
be emitted by filament because of
electrostatic repulsion
Space Charge Effect
The x-ray tube current is adjusted by
controlling…
the filament current
Filament current that has risen to its
maximum value because all available
electrons have been used
Saturation Current
A region of the anode target in which
electrons interact to produce x-rays, actual x-ray source
Focal Spot
Important for high resolution magnification
radiography & mammography
Round Focal Spot
It is used when small body parts are image
& when better spatial resolution is required
Small Focal Spot
It is used when large body parts are imaged
Large Focal Spot
The positive side of the x-ray tube
Anode
3 Most Common Anode Materials
Copper (Cu-29), Molybdenum (Mo-
42) & Graphite
It is used when high tube current & power
are not required
Stationary Anode
The area of the anode struck by the electrons
from the cathode
Target
The material of choice for the target
Tungsten (Z=74)
3 Main Reasons why Tungsten is the material of choice
High Atomic Number
Thermal Conductivity
High Melting Point
It allows the electron beam to interact with a
much larger target area
Rotating Anode
Higher tube currents and shorter exposure
times are possible with…
the rotating anode
The shaft between the anode & the rotor
Anode Stem
It is used to turn the anode
Electromagnetic Induction Motor
2 principal parts of Electromagnetic Induction Motor
stator & rotor
Located outside the enclosure
Stator
Located inside the glass envelope
Rotor
Time it takes the rotor to rest after use (60s)
Coast Time
the ability of the cone of xrays produced to adequately cover the largest field size used
Line Focus Principle
The area projected onto the patient & image
receptor
Effective Focal Spot/Effective Target Area
Consequence of line focus principle
Anode Heel Effect
The imaginary line generated by the
centermost x-ray in the beam
Central Ray
X-rays produced in the anode but not at the
focal spot
Off-Focus Radiation/Extrafocal X-rays
Three Ways of Heat Dissipation
Radiation, Conduction & Convection
The transfer of heat by the emission of
infrared radiation
Radiation
The transfer of energy from one area of an
object to another
Convection
The transfer of heat by the movement of a
heated substance from one place to another
Convection
It guides & aids the radiographer in using xray tubes & acceptable exposure levels to
maximize x-ray tube life
X-ray Tube Rating Chart
Three Types of Rating Charts
- Radiographic Rating Chart
- Anode Cooling Chart
- Housing Cooling Chart
It conveys which radiographic techniques
are safe & unsafe for x-ray tube operation
Radiographic Rating Charts