Zzzz Flashcards
Heart of Xray Machines
Xray Tube
A special type of diode
Xray Tube
electronic component that has 2 electrodes
Diode
Converts electrical energy to electromagnetic energy
Xray Tube
Components
Cathode Assembly
Anode Assembly
Glass/ Metal Enclosure
Glass Housing
negatively charged electrode
Cathode
Small coil of wire made of thoriated tungsten
Filament
Filament Measurement
2mm wide, 1 or 2cm long
Process where a heated material ejects electrons
Thermionic Emission
most common cause of tube failure
Tungsten Vaporization
enhances efficiency of thermionic emission
1-2% Thorium
- metal shroud that surrounds the filament.
- negatively charged to electrostatically confine the electron beam to a small area
- designed to concentrate and direct electrons on a single narrow path toward the target.
- it serves as a grid or exposure switch in a grid- controlled x-ray tube
-adjacent to the filament
Focusing Cup
Factors that affect the focusing cups efficiency
- size and shape
- Charge
- Filament size and shape
- Position of the filament
Dense cloud of electrons that force near the filament
Space Charge
phenomenon that makes it harder for the filament to emit more electrons limiting the electron flow
Space charge effect
the force that pushes object with the same electric charge, pushes each other because like charges repel
Electrostatic Repulsion
- positively charged electrode
- conducts electricity, radiates heat and contains the target
Anode Assembly
2 types of anode assembly:
Stationary n Rotating
3 main functions of anode
- Electrical Conductor
- Support for the target
- Thermal/ Heat Dissipator
Common materials used in anode assembly
Copper 29
Molybdenum 42
Graphite
Target is fixed. It is used when high tube current and power are not required
Stationary Anode
Rotating Anode
- allows electron beam to interact with a larger target area
- used in general radiography
roating anode rotates at about
3600-10000rpm
- Shaft between anode and rotor
- Composition Mo
Anode Stem
The area of the cathode that heats and produces x-ray
Target
Tungsten preferred target material
- High Atomic No.
- Thermal Conductivity
- High Melting Point
gives enhanced mechanical strength- mechanical stress caused by high speed rotation, and also reduces brittleness
Tungsten with Rhenium
Mammographic targets
Mo z=42 and Rh z=45
- the actual Xray source - where the xrays are produced/ emitted
- A region among the anode target where the accelerated electrons from the cathode bombard or strike
Focal Spot
Helps improve sharpness and clarity of the images
High resolution magnification radiography and mammography
Round Focal Spot
Associated with small filament.
Used when high detail and clarity are needed.
Small Focal Spot
associated with large filament
used when imaging larger body parts as it can handle higher amounts of energy
Large Focal Spot
- is used to rotate the anode in an xray tube
Electromagnetic Induction Motor
located outside the enclosure- stationary coil windings contain electromagnets
Consists of series of electromagnets arranged evenly
Stator
inside the glass enclosure
Composition: copper and soft iron bars fused together into a single ??
Rotor
External components
Support structures,
protective housing,
glass and metal enclosure
made of Pyrex or borosilicate glass able to withstand the tremendous heat generated.
Glass Enclosure
the natural capacity of the glass to filter or to block some of the low energy xrays
Inherent Filtration
a segment of glass that is thinner than the rest
Tube Window
- helps keep electric potential between the electrons of the tube current and the enclosure
- Advantage: less likely to fail and has longer tube life
Metal Enclosure
insulator protective housing that prevents electric shock
Diala Oil
- protect it from damage from rough handling
- is usually the one being handled
Protective Housing
