Two Internal Structures of the X -RayTube Flashcards
electrical device used to generate x-rays
converts electrical energy to x-radiation
X-Ray Tube
Most important component of the radiographic system because it is where the x ray is produced
X-Ray Tube
Size of X-Ray Tube
30 to 50 cm long; 20 cm in diameter
Two Internal Structures of X-ray Tube
Cathode and Anode
Two parts of Cathode and their material
o Filament (small coil made up of thoriated tungsten)
o Focusing Cup (made up of NICKEL)
Location of the Filament
Inside the focusing cup
Filament is controlled by ——, which is ——
- Controlled by mAs
- mAs is directly proportional
The area where high-speed electrons are produced
Filament
Modern x-ray tubes contain two filaments, what are they?
Small Filament & Large Filament
Size of Filament
o Usually about 2 mm in diamter
o 1 cm long: Small Filament
o 2 cm long: Large Filament
Once the filament is heated, it will release electrons which produce an ——?
electron cloud or space charged electron
repulsion of the space charge or electrostatic repulsion
Space Charge Effect
As the space charge becomes more negative by boiling off more electrons, it makes it difficult for the electron to be emitted
Space Charge Effect
the outer shell electrons of the filament is “boiled off”
Thermionic Emission
3 Characteristics of Tungsten
- makes up the Filament
- Provides higher thermionic emission than other metals (thermal conductivity)
- Has a very HIGH MELTING POINT
High Melting Point of Tungsten
3410 C
metal cup where the filament is embedded
o Focusing Cup
Designed to condensed electron beam to small area on focal track
o Focusing Cup
4 FACTORS THAT DETERMINES THE EFFECTIVENESS OF THE CUP
i. Size and Shape
ii. Charge
iii. Filament Size
iv. Position of Filament within the Cup
Three Characteristics of Anode
- Mechanical support for the target
- Dissipates heat
- Electrical conductor
Two parts of an Anode and their material
- Target (made up from an alloy of TUNGSTEN AND RHENIUM)
- Focal Spot [GRACOMO (Graphite, Copper, Molybdenum)]
the area of the anode struck by the projectile electrons
Target
actual source of radiation
Focal Spot
The Focal Spot is controlled through the ——?
Operating Console
The smaller the focal spot, the ——?
the better the resolution of the resultant image (higher spatial resolution and radiographic detail)
Sizes of Focal Spot and their measurements
- Small Focal Spot (range of 0.1 mm to 0.5 mm)
- Large Focal Spot (0.4 mm to 1.2 mm)
For small extremities and is used when better spatial resolution is required
Small Focal Spot
Used when technical factors that produce high heat are required (High exposure)
Large Focal Spot
Two types of Anode
- Rotating Anode
- Stationary Anode
- shaped like a beveled disc
- Used in general purpose x-ray tubes
- Provides greater target area and heat dissipation
- Has the ability to attain greater exposure loads by providing a larger area for the electron beam to interact with the target
Rotating Anode
Characteristics of Rotating Anode
- Complex Design;
- High Heat Capacity;
- Used for High Exposures
- Made up of a tungsten target, embedded with a large copper bar
- Used in other specialized units in which high tube current and power are not required
- Used in dental x-rays
Stationary Anode
Characteristics of Stationary Anode
- Simple design;
- Low Heat Capacity;
- Used for Low Exposures
Was incorporated into X-ray tube targets to allow a large area for heating while maintaining a small focal spot.
Line Focus Principle
The advantage of LFP
provides the detail of small focal spot while allowing the large amount of heat dissipation.
It is the electron bombarde by the cathode travelling to the anode.
Incident Electron Beam
The size of the incident electron beam is determined by the ———?
width of the filament.
Physical area of the anode that when bombarded by the electron beam emits X-ray.
Actual Focal Spot
The Actual Focal Spot is determined by ———?
- width of the incident electron beam,
- construction of the focusing cup and,
- position of the filament in the focusing cup.
Area projected onto the patient
Effective Focal Spot
Pros of Small Actual Focal Spot
- Thin body parts
- Small effective focal spot
Con of Small Actual Focal Spot
- Poor heat dissipation
Pros of Large Actual Focal Spot
- Good heat dissipation
- Thick body parts
- Short exposure time
Con of Large Actual Focal Spot
- Long effective focal spot
Pro of Smaller Anode Angle
Small effective focal spot
(INCREASED SPATIAL RESOLUTION)
Con of Smaller Anode Angle
- Limits the size of usable field
